U.S. patent application number 14/950288 was filed with the patent office on 2016-04-21 for methods and compositions for concrete production.
The applicant listed for this patent is CarbonCure Technologies Inc.. Invention is credited to Joshua Jeremy Brown, Kevin Cail, Dean Paul Forgeron, Mark MacDonald, George Sean Monkman, Paul J. Sandberg.
Application Number | 20160107939 14/950288 |
Document ID | / |
Family ID | 55748496 |
Filed Date | 2016-04-21 |
United States Patent
Application |
20160107939 |
Kind Code |
A1 |
Monkman; George Sean ; et
al. |
April 21, 2016 |
METHODS AND COMPOSITIONS FOR CONCRETE PRODUCTION
Abstract
The invention provides compositions and methods directed to
carbonation of a cement mix during mixing. The carbonation may be
in a stationary mixer or a transportable mixer, such as a drum of a
ready-mix truck.
Inventors: |
Monkman; George Sean;
(Montreal, CA) ; Cail; Kevin; (Sarasota, FL)
; Sandberg; Paul J.; (Beverly, MA) ; MacDonald;
Mark; (Halifax, CA) ; Brown; Joshua Jeremy;
(Lower Sackville, CA) ; Forgeron; Dean Paul;
(White's Lake, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CarbonCure Technologies Inc. |
Dartmouth |
|
CA |
|
|
Family ID: |
55748496 |
Appl. No.: |
14/950288 |
Filed: |
November 24, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14701456 |
Apr 30, 2015 |
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14950288 |
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PCT/CA2014/050611 |
Jun 25, 2014 |
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14701456 |
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14249308 |
Apr 9, 2014 |
9108883 |
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PCT/CA2014/050611 |
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61839312 |
Jun 25, 2013 |
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61847254 |
Jul 17, 2013 |
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61879049 |
Sep 17, 2013 |
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61925100 |
Jan 8, 2014 |
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61938063 |
Feb 10, 2014 |
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61980505 |
Apr 16, 2014 |
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62083784 |
Nov 24, 2014 |
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62096018 |
Dec 23, 2014 |
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62160350 |
May 12, 2015 |
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62165670 |
May 22, 2015 |
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62240843 |
Oct 13, 2015 |
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62086024 |
Dec 1, 2014 |
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62146103 |
Apr 10, 2015 |
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61839312 |
Jun 25, 2013 |
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61847254 |
Jul 17, 2013 |
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61879049 |
Sep 17, 2013 |
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61925100 |
Jan 8, 2014 |
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61938063 |
Feb 10, 2014 |
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Current U.S.
Class: |
106/638 ;
366/12 |
Current CPC
Class: |
C04B 28/02 20130101;
C04B 40/0032 20130101; C04B 2111/00017 20130101; Y02P 40/18
20151101; B28C 5/0806 20130101; B28C 5/46 20130101; B28C 5/1856
20130101; B28C 5/4203 20130101; C04B 40/0231 20130101; C04B 40/0231
20130101; C04B 28/04 20130101; B28C 7/04 20130101; C04B 22/10
20130101; B28C 5/003 20130101 |
International
Class: |
C04B 40/02 20060101
C04B040/02; B28C 5/18 20060101 B28C005/18; B28C 5/08 20060101
B28C005/08 |
Claims
1. A method for carbonating a concrete mix comprising a type of
cement comprising delivering dose of CO2 to the concrete mix while
it is mixing in a mixer, wherein the delivery of the carbon dioxide
commences within 3 minutes of the start of mixing of the concrete
mix, and wherein the duration of the delivery of the carbon dioxide
is 10 seconds to 4 minutes.
2. The method of claim 1 wherein the dose of carbon dioxide is
0.01-1.0% by weight cement (bwc).
3. The method of claim 1 wherein the delivery of the carbon dioxide
commences within 1 minute of the start of mixing of the concrete
mix.
4. The method of claim 1 wherein the mixer comprises a
transportable mixer.
5. The method of claim 4 wherein the mixer comprises a drum of a
ready-mix truck.
6. The method of claim 1 wherein the dose of carbon dioxide is
based on previous testing of a plurality of doses of carbon dioxide
on a plurality of test mixes, wherein the test mixes comprise the
type of cement in the concrete mix.
7. The method of claim 6 wherein at least three test doses of
carbon dioxide are used in the previous testing.
8. The method of claim 6 wherein the plurality of doses of carbon
dioxide used in the previous testing are all 0.01-1.0% bwc, and the
dose of carbon dioxide delivered to the mixing concrete is
0.01-1.0% bwc.
9. The method of claim 1 wherein the carbon dioxide is delivered
via a conduit to the surface of the mixing concrete.
10. The method of claim 9 wherein the conduit is positioned to be
5-200 cm from the surface of the mixing concrete, on average.
11. The method of claim 1 wherein the carbon dioxide is delivered
as a mixture of solid and gaseous carbon dioxide.
12. A method for carbonating a concrete mix in a drum of a
ready-mix truck comprising (i) positioning a first conduit for
delivery of components of the concrete mix to the drum, wherein the
first conduit contains a second conduit for delivery of carbon
dioxide to the concrete mix, and wherein the components of the
concrete mix comprise at least cement and water; (ii) delivering
the components of the concrete mix to the drum via the first
conduit to provide a concrete mix in the drum; (iii) mixing the
concrete mix; and (iv) delivering a dose of carbon dioxide to the
mixing concrete via an opening of the second conduit.
13. The method of claim 12 wherein the dose of carbon dioxide is
0.01-1.5% by weight cement.
14. The method of claim 12 wherein the carbon dioxide is a mixture
of solid and gaseous carbon dioxide.
15. The method of claim 12 wherein the dose of carbon dioxide is
based on previous testing of a plurality of doses of carbon dioxide
on a plurality of test mixes, wherein the test mixes comprise the
type of cement in the concrete mix.
16. The method of claim 15 wherein at least three test doses of
carbon dioxide are used in the previous testing.
17. The method of claim 15 wherein the plurality of doses of carbon
dioxide used in the previous testing are all 0.01-1.0% bwc, and the
dose of carbon dioxide delivered to the mixing concrete is
0.01-1.0% bwc.
18. The method of claim 12 wherein the opening of the second
conduit is positioned to be 5 cm to 200 cm, on average, from a
surface of the mixing concrete.
19. An apparatus for delivering carbon dioxide to a drum of a
ready-mix truck comprising (i) a first conduit configured for
delivery of components of concrete to the drum of the ready-mix
truck; (ii) a second conduit contained within or attached to the
first conduit configured for delivery of carbon dioxide to the drum
of the ready-mix truck.
20. The apparatus of claim 19 wherein the second conduit is made of
material that is sufficiently flexible to move with the first
conduit.
21. The apparatus of claim 19 wherein the second conduit contains a
third conduit, wherein the third conduit is configured to be
extended from the second conduit when the first conduit is
positioned to deliver the components of the concrete to the drum,
and to be retracted when the first conduit is moved from the drum
of the ready-mix truck
Description
CROSS-REFERENCE
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 14/701,456, filed Apr. 30, 2015, which is a
continuation of PCT Application No. PCT/CA2014/050611 filed Jun.
25, 2014, which claims the benefit of U.S. Provisional Patent
Application Ser. No. 61/980,505, filed Apr. 16, 2014 and is a
continuation-in-part of U.S. patent application Ser. No.
14/249,308, filed Apr. 9, 2014 (now U.S. Pat. No. 9,108,883 issued
Aug. 18, 2015), which claim the benefit of U.S. Provisional Patent
Application Ser. No. 61/839,312, filed Jun. 25, 2013, U.S.
Provisional Patent Application Ser. No. 61/847,254, filed Jul. 17,
2013, U.S. Provisional Patent Application Ser. No. 61/879,049,
filed Sep. 17, 2013, U.S. Provisional Patent Application Ser. No.
61/925,100, filed Jan. 8, 2014, U.S. Provisional Patent Application
Ser. No. 61/938,063, filed Feb. 10, 2014. This application also
claims the benefit of U.S. Provisional Patent Application Ser. No.
62/083,784, filed Nov. 24, 2014, U.S. Provisional Patent
Application Ser. No. 62/096,018, filed Dec. 23, 2014, U.S.
Provisional Patent Application Ser. No. 62/160,350, filed May 12,
2015, U.S. Provisional Patent Application Ser. No. 62/165,670 filed
May 22, 2015, U.S. Provisional Patent Application Ser. No.
62/240,843, filed Oct. 13, 2015, U.S. Provisional Patent
Application Ser. No. 62/086,024, filed Dec. 1, 2014, and U.S.
Provisional Patent Application Ser. No. 62/146,103, filed Apr. 10,
2015, all of which are incorporated herein by reference in their
entireties.
BACKGROUND
[0002] Cement mixes, such as concrete mixes, are used in a
multitude of compositions and procedures throughout the world. In
addition, greenhouse gases such as carbon dioxide are a growing
concern worldwide. There is a need for methods and compositions to
contact cement mixes with carbon dioxide and for cement mixes
containing incorporated carbon dioxide and carbonation
products.
SUMMARY OF THE INVENTION
[0003] In one aspect, the invention provides methods.
[0004] In certain embodiments, the invention provides a method for
carbonating a concrete mix comprising a type of cement that
includes delivering dose of CO2 to the concrete mix while it is
mixing in a mixer, where the delivery of the carbon dioxide
commences within 3 minutes of the start of mixing of the concrete
mix, and wherein the duration of the delivery of the carbon dioxide
is 10 seconds to 4 minutes. In certain embodiments, the dose of
carbon dioxide is 0.01-1.0% by weight cement (bwc). In certain
embodiments, the delivery of the carbon dioxide commences within 1
minute of the start of mixing of the concrete mix. The mixer can be
any suitable mixer, such as a stationary mixer or a transportable
mixer; in certain embodiments, the mixer comprises a transportable
mixer, e.g., a drum of a ready-mix truck. In certain embodiments,
the dose of carbon dioxide is based on previous testing of a
plurality of doses of carbon dioxide on a plurality of test mixes,
wherein the test mixes comprise the type of cement in the concrete
mix, for example at least three test doses of carbon dioxide can be
used in the previous testing. In certain embodiments, the plurality
of doses of carbon dioxide used in the previous testing are all
0.01-1.0% bwc, and the dose of carbon dioxide delivered to the
mixing concrete is 0.01-1.0% bwc. The carbon dioxide can be
delivered via a conduit to the surface of the mixing concrete, for
example, a conduit positioned to be 5-200 cm from the surface of
the mixing concrete, on average. In certain embodiments, the carbon
dioxide is delivered as a mixture of solid and gaseous carbon
dioxide.
[0005] In certain embodiments, the invention provides a method for
carbonating a concrete mix in a drum of a ready-mix truck
comprising (i) positioning a first conduit for delivery of
components of the concrete mix to the drum, wherein the first
conduit contains a second conduit for delivery of carbon dioxide to
the concrete mix, and wherein the components of the concrete mix
comprise at least cement and water; (ii) delivering the components
of the concrete mix to the drum via the first conduit to provide a
concrete mix in the drum; (iii) mixing the concrete mix; and (iv)
delivering a dose of carbon dioxide to the mixing concrete via an
opening of the second conduit. In certain embodiments, the dose of
carbon dioxide is 0.01-1.5% by weight cement. In certain
embodiments, the carbon dioxide is a mixture of solid and gaseous
carbon dioxide. In certain embodiments, the dose of carbon dioxide
is based on previous testing of a plurality of doses of carbon
dioxide on a plurality of test mixes, wherein the test mixes
comprise the type of cement in the concrete mix. In certain
embodiments, at least three test doses of carbon dioxide are used
in the previous testing. In certain embodiments, the plurality of
doses of carbon dioxide used in the previous testing are all
0.01-1.0% bwc, and the dose of carbon dioxide delivered to the
mixing concrete is 0.01-1.0% bwc. In certain embodiments, the
opening of the second conduit is positioned to be 5 cm to 200 cm,
on average, from a surface of the mixing concrete.
[0006] In another aspect, the invention provides apparatus. In
certain embodiments, the invention provides an apparatus for
delivering carbon dioxide to a drum of a ready-mix truck comprising
(i) a first conduit configured for delivery of components of
concrete to the drum of the ready-mix truck; and (ii) a second
conduit contained within or attached to the first conduit
configured for delivery of carbon dioxide to the drum of the
ready-mix truck. In certain embodiments the second conduit is made
of material that is sufficiently flexible to move with the first
conduit. In certain embodiments, the second conduit contains a
third conduit, wherein the third conduit is configured to be
extended from the second conduit when the first conduit is
positioned to deliver the components of the concrete to the drum,
and to be retracted when the first conduit is moved from the drum
of the ready-mix truck
INCORPORATION BY REFERENCE
[0007] All publications, patents, and patent applications mentioned
in this specification are herein incorporated by reference to the
same extent as if each individual publication, patent, or patent
application was specifically and individually indicated to be
incorporated by reference.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The novel features of the invention are set forth with
particularity in the appended claims. A better understanding of the
features and advantages of the present invention will be obtained
by reference to the following detailed description that sets forth
illustrative embodiments, in which the principles of the invention
are utilized, and the accompanying drawings of which:
[0009] FIG. 1 provides a schematic view of a stationary mixer with
apparatus for providing carbon dioxide to a hydraulic cement mix
during mixer.
[0010] FIG. 2 provides a schematic view of a mobile mixer (ready
mix truck) provided with a detachable carbon dioxide delivery
system to deliver carbon dioxide to the mixing concrete.
[0011] FIG. 3 provides a schematic view of a mobile mixer (ready
mix truck) provided with an attached carbon dioxide delivery system
to deliver carbon dioxide to the mixing concrete.
[0012] FIG. 4 shows 7-day compressive strengths of concrete
prepared from wet mixes exposed to carbon dioxide at various
doses.
[0013] FIG. 5 shows 7-day compressive strengths of concrete
prepared from wet mixes exposed to carbon dioxide at various doses
and with various water contents.
[0014] FIG. 6 shows 7-day compressive strengths of concrete
prepared from wet mixes exposed to carbon dioxide at various
doses.
[0015] FIG. 7 shows 14-day compressive strengths of concrete
prepared from wet mixes exposed to carbon dioxide at various
doses.
[0016] FIG. 8 shows 28-day compressive strengths of concrete
prepared from wet mixes exposed to carbon dioxide at various
doses.
[0017] FIG. 9 shows 7-, 14-, and 28-day compressive strengths of
concrete prepared from wet mixes exposed to carbon dioxide with two
different water contents.
[0018] FIG. 10 shows 7- and 28-day compressive strengths of
concrete prepared from wet mixes exposed to carbon dioxide at two
different doses and two different water contents.
[0019] FIG. 11 shows 7-day compressive strengths of concrete
prepared from wet mixes exposed to carbon dioxide at two different
doses and higher water content.
[0020] FIG. 12 shows 7-day compressive strengths of concrete
prepared from wet mixes exposed to carbon dioxide at two different
doses and higher water content.
[0021] FIG. 13 shows 7-day compressive strengths of concrete
prepared from wet mixes exposed to carbon dioxide at two different
doses and higher water content.
[0022] FIG. 14 shows slump of concrete wet mixes exposed to carbon
dioxide at two different doses and five different water
contents.
[0023] FIG. 15 provides a graphic illustration of slump at various
times after truck arrival for carbonated concrete batches prepared
in a ready mix operation.
[0024] FIG. 16 provides a graphic illustration of compressive
strength development in carbonated concrete prepared in a ready mix
operation, compared to control, uncarbonated concrete, at 3, 7, 28,
and 56 days.
[0025] FIG. 17A provides a graphic illustration of Rapid chloride
penetration tests
[0026] FIG. 17B provides a graphic illustration of Flexural
strength tests on carbonated concrete prepared in a ready mix
operation compared to control, uncarbonated concrete.
[0027] FIG. 18 provides a graphic illustration of compressive
strengths at 1, 7, 28, and 56 days for concretes prepared in a
ready mix operation with 0, 0.5, or 1.0% bwc carbon dioxide
delivered to the concrete.
[0028] FIG. 19 provides a graphic illustration of compressive
strengths at 1, 7, 28, and 56 days for concretes prepared in a
ready mix operation with 0, 1.0, or 1.5% bwc carbon dioxide
delivered to the concrete, and 0.05% sodium gluconate admixture
added to the 1.5% batch.
[0029] FIG. 20 provides a graphic illustration of cylinder mass for
constant volume cylinders (density), a proxy for compressive
strength, in dry cast concrete prepared as uncarbonated or
carbonated for 1 or 2 minutes, with addition of sodium gluconate
admixture at various concentrations.
[0030] FIG. 21 provides a graphic illustration of cylinder mass for
constant volume cylinders (density), a proxy for compressive
strength, in dry cast concrete prepared as uncarbonated or
carbonated for 90 s at 50 LPM with addition of sodium gluconate
admixture at 0.24, 0.30, 0.36, or 0.42% bwc.
[0031] FIG. 22 provides a graphic illustration of cylinder mass for
constant volume cylinders (density), a proxy for compressive
strength, in dry cast concrete prepared as uncarbonated or
carbonated for 90 s at 50 LPM with addition of sodium gluconate
admixture at 0.30 or 0.42% bwc.
[0032] FIG. 23 provides a graphic illustration of cylinder mass for
constant volume cylinders (density), a proxy for compressive
strength, in dry cast concrete prepared as uncarbonated or
carbonated for 90 s at 50 LPM with addition of sodium gluconate
admixture at 0.30 or 0.42% bwc. All samples included Rainbloc and
Procast admixtures, with one 0.30% sample having Procast added
after carbon dioxide delivery.
[0033] FIG. 24 provides a graphic illustration of slump, relative
to untreated control, in carbonated mortar mixes treated with
sodium glucoheptonate, fructose, or sodium gluconate at various
concentrations.
[0034] FIG. 25 provides a graphic illustration of effects on slump
of fructose or sodium gluconate added to a mortar mix pre-, mid-,
or post-carbonation.
[0035] FIG. 26 provides a graphic illustration of effects on
24-hour compressive strength, compared to uncarbonated control, of
a carbonated mortar preparation in which sodium gluconate was added
either before or after carbonation at doses of 0, 0.025, 0.05, and
0.75%.
[0036] FIG. 27 provides a graphic illustration of the effects of
temperature of materials on rate of carbon dioxide uptake in a
mortar mix. Temperatures were 7.degree. C., 15.degree. C. and
25.degree. C.
[0037] FIG. 28 provides a graphic illustration of the effects of
heated or cold gases, or dry ice, on carbon dioxide uptake in a
cement paste system.
[0038] FIG. 29 provides a graphic illustration of the effects of
plasticizers and calcium hydroxide on 24 hour compressive strength
in carbonated and uncarbonated mortar mixes.
[0039] FIG. 30 provides a graphic illustration of the effects of
CaO, NaOH, Ca(NO.sub.2).sub.2, and CaCl.sub.2 on 24 hour
compressive strength in carbonated and uncarbonated mortar mix.
[0040] FIG. 31 provides a graphic illustration of the effect of
carbon dioxide addition before or after the addition of an air
entrainer on mortar density.
[0041] FIG. 32 provides a table showing the results of tests for
carbon dioxide uptake, compressive strength, water absorption, and
density for blocks produced in a precast dry cast operation with
carbonation at the mixer, feedbox, or both, in a standard block
mix.
[0042] FIG. 33 is a graphic illustration of the effects of sodium
gluconate dose on 7-, 28- and 56-day compressive strengths of
carbonated blocks produced in a dry cast operation, with various
doses of sodium gluconate, compared to uncarbonated control.
[0043] FIG. 34 provides a table showing the results of tests for
carbon dioxide uptake, compressive strength, water absorption, and
density for blocks produced in a precast dry cast operation with
carbonation at the mixer in a limestone block mix.
[0044] FIG. 35 provides a table showing the results of tests for
carbon dioxide uptake, compressive strength, water absorption, and
density for blocks produced in a precast dry cast operation with
carbonation at the mixer in a lightweight block mix.
[0045] FIG. 36 provides a graphic illustration of 7-, 28-, and
56-day compressive strengths of lightweight blocks produced in a
dry cast operation with carbonation and various doses of sodium
gluconate.
[0046] FIG. 37 provides a table showing the results of tests for
carbon dioxide uptake, compressive strength, water absorption, and
density for blocks produced in a precast dry cast operation with
carbonation at the mixer in a sandstone block mix.
[0047] FIG. 38 provides a graphic illustration of 7-, 28-, and
56-day compressive strengths of sandstone blocks produced in a dry
cast operation with carbonation and various doses of sodium
gluconate.
[0048] FIG. 39 provides a graphic illustration of the relationship
between optimum dose of sodium gluconate and cement content in
carbonated dry cast blocks.
[0049] FIG. 40 provides a graphic illustration of compressive
strength and density of carbonated and uncarbonated precast medium
weight blocks, with or without treatment with 0.25% sodium
gluconate.
[0050] FIG. 41 provides a table of results of third party testing
of medium weight blocks produced in a precast operation as
uncarbonated, carbonated, and carbonated+0.25% sodium gluconate, as
strength, absorption, and shrinkage.
[0051] FIG. 42 provides a graphic illustration of the effect of
cement type on carbon dioxide uptake in a mortar mix.
[0052] FIG. 43 provides a graphic illustration of the effects of
temperature of materials on slump, relative to control, in
carbonated mortar mixes. Temperatures were 7.degree. C., 15.degree.
C. and 25.degree. C.
[0053] FIG. 44 provides a graphic illustration of the effect of w/c
ratio on carbon dioxide uptake in a mortar mix.
[0054] FIG. 45 provides a graphic illustration of the effect of w/c
ratio on carbon dioxide uptake in a mortar mix.
[0055] FIG. 46 provides a graphic illustration of the effect of w/c
ratio on carbon dioxide uptake in a concrete mix.
[0056] FIG. 47 provides a graphic illustration of the relationship
between carbon dioxide uptake and temperature rise in a mortar mix
at various w/c.
[0057] FIG. 48 provides a graphic illustration of the relationship
between carbon dioxide uptake and temperature rise in mortar mixes
prepared from cements from Holcim GU, Lafarge Quebec, and Lehigh,
at w/c of 0.5.
[0058] FIG. 49 provides a graphic illustration of the effects of
sodium gluconate at 0, 0.1%, or 0.2%, added after carbonation to a
concrete mix on slump at 1, 10, and 20 minutes.
[0059] FIG. 50 provides a graphic illustration of the effects of
fructose on initial slump of carbonated concrete mix.
[0060] FIG. 51 provides a graphic illustration of the effects of
fructose on 24-hour and 7-day compressive strength in a carbonated
concrete mix.
[0061] FIG. 52 provides a graphic illustration of the relationship
between surface area compressive strength at 24 hours of carbonated
mortars produced with different cements.
[0062] FIG. 53 provides a graphic illustration of carbon dioxide
dosing (top line), carbon dioxide uptake (second line from top),
and carbon dioxide detected at two sensors (bottom two lines) in a
precast mixing operation where carbon dioxide flow was adjusted
according to the carbon dioxide detected by the sensors.
[0063] FIG. 54 shows isothermal calorimetry curves in mortar
prepared with Holcim GU cement carbonated at low levels of
carbonation.
[0064] FIG. 55 shows total heat evolution at various time points in
mortar prepared with Holcim GU cement carbonated at low levels of
carbonation.
[0065] FIG. 56 shows set, as represented by penetrometer readings,
in mortar prepared with Holcim GU cement carbonated at a low level
of carbonation.
[0066] FIG. 57 shows isothermal calorimetry curves in mortar
prepared with Lafarge Brookfield GU cement carbonated at low levels
of carbonation.
[0067] FIG. 58 shows 8 hour and 24 hour compressive strengths in
mortar prepared with Lafarge Brookfield GU cement carbonated at low
levels of carbonation.
[0068] FIG. 59 shows isothermal calorimetry curves in concrete
prepared with Lafarge Brookfield GU cement carbonated at low levels
of carbonation.
[0069] FIG. 60 shows calorimetry energy curves in concrete prepared
with Lafarge Brookfield GU cement carbonated at low levels of
carbonation.
[0070] FIG. 61 shows 8 hour and 12 hour compressive strengths in
concrete prepared with Lafarge Brookfield GU cement carbonated at
low levels of carbonation.
[0071] FIG. 62 shows set, as represented by penetrometer readings,
in mortar prepared with Lafarge Brookfield GU cement carbonated at
a low level of carbonation.
[0072] FIG. 63 shows 8 hour and 12 hour compressive strengths in
concrete prepared with St. Mary's Bowmanville GU cement carbonated
at low levels of carbonation.
[0073] FIG. 64 shows 12-hour compressive strengths of concrete
carbonated at various low doses of carbonation.
[0074] FIG. 65 shows 16-hour compressive strengths of concrete
carbonated at various low doses of carbonation
[0075] FIG. 66 shows 24-hour compressive strengths of concrete
carbonated at various low doses of carbonation.
[0076] FIG. 67 shows 7-day compressive strengths of concrete
carbonated at various low doses of carbonation.
[0077] FIG. 68 shows carbon dioxide uptake of dry mix concrete at
various doses of sodium gluconate.
[0078] FIG. 69 shows compacted cylinder mass (a proxy for density)
related to sodium gluconate dose in carbonated and uncarbonated dry
mix concrete.
[0079] FIG. 70 shows the data of FIG. 69 normalized to control.
[0080] FIG. 71 shows 6 hour energy released related to sodium
gluconate dose in carbonated and uncarbonated dry mix concrete.
[0081] FIG. 72 shows the data of FIG. 71 normalized to control.
[0082] FIG. 73 shows rates of CO.sub.2 uptake in mortars prepared
with added CaO, NaOH, or CaCl2, or no additive.
[0083] FIG. 74 shows a summary of calorimetry data for mortars
prepared with and without added CaO and exposed to carbon dioxide
for various lengths of time while mixing, as well as carbon dioxide
uptake.
[0084] FIG. 75 shows relative comparison of energy released by
mortar mixes with no added CaO subjected to carbonation, compared
to uncarbonated control.
[0085] FIG. 76 shows a relative comparison of energy released by
CaO-doped mortar mixes exposed to carbon dioxide for various times,
compared to mortar mixes with no added CaO exposed to carbon
dioxide for the same time periods.
[0086] FIG. 77A shows calorimetry data for the CO2-1, -2, and -3
mixes of Example 28, and uncarbonated control, power vs. time.
[0087] FIG. 77B shows calorimetry data for the CO2-1, -2, and -3
mixes of Example 28, and uncarbonated control, energy vs. time.
[0088] FIG. 78A shows calorimetry data for the CO2-4, -5, and -6
mixes of Example 28, and uncarbonated control, power vs. time.
[0089] FIG. 78B shows calorimetry data for the CO2-4, -5, and -6
mixes of Example 28, and uncarbonated control.
[0090] FIG. 79A shows calorimetry data for the CO2-1, -2, and -3
mixes of Example 29, and uncarbonated control, power vs. time.
[0091] FIG. 79B shows calorimetry data for the CO2-1, -2, and -3
mixes of Example 29, and uncarbonated control.
[0092] FIG. 80A shows calorimetry data for the CO2-5, and -6 mixes
of Example 29, and uncarbonated control, power vs. time.
[0093] FIG. 80B shows calorimetry data for the CO2-5, and -6 mixes
of Example 29, and uncarbonated control.
[0094] FIG. 81 shows compressive strengths at 24 hours for control
and three different doses of carbon dioxide of the first day of the
trial of Example 30.
[0095] FIG. 82 shows compressive strengths at 3 days for control
and three different doses of carbon dioxide of the first day of the
trial of Example 30.
[0096] FIG. 83 shows compressive strengths at 7 days for control
and three different doses of carbon dioxide of the first day of the
trial of Example 30.
[0097] FIG. 84 shows compressive strengths at 28 days for control
and three different doses of carbon dioxide of the first day of the
trial of Example 30.
[0098] FIG. 85 shows compressive strengths at 56 days for control
and three different doses of carbon dioxide of the first day of the
trial of Example 30.
[0099] FIG. 86A shows calorimetry data for the CO2-1 (1402), -2
(1403), and -3 (1404) mixes of the first day of the trial of
Example 30, and uncarbonated control (1401), power vs. time.
[0100] FIG. 86B shows calorimetry data for the CO2-1 (1402), -2
(1403), and -3 (1404) mixes of the first day of the trial of
Example 30, and uncarbonated control (1401), energy vs. time.
[0101] FIG. 87 shows compressive strengths at 24 hours for control
and one dose of carbon dioxide of the second day of the trial of
Example 30.
[0102] FIG. 88 shows compressive strengths at 3 days for control
and one dose of carbon dioxide of the second day of the trial of
Example 30.
[0103] FIG. 89 shows compressive strengths at 7 days for control
and one dose of carbon dioxide of the second day of the trial of
Example 30.
[0104] FIG. 90 shows compressive strengths at 28 days for control
and one dose of carbon dioxide of the second day of the trial of
Example 30.
[0105] FIG. 91 shows compressive strengths at 56 days for control
and one dose of carbon dioxide of the second day of the trial of
Example 30.
[0106] FIG. 92A shows calorimetry data for the CO2-1 and -2 mixes
of the second day of the trial of Example 30, and uncarbonated
controls 1 and 2, power vs. time.
[0107] FIG. 92B shows calorimetry data for the CO2-1 and -2 mixes
of the second day of the trial of Example 30, and uncarbonated
controls 1 and 2, energy vs. time.
[0108] FIG. 93A shows calorimetry data for the three doses of
carbon dioxide of Example 31, and uncarbonated control, power vs.
time.
[0109] FIG. 93B shows calorimetry data for the three doses of
carbon dioxide of Example 31, and uncarbonated control, energy vs.
time.
[0110] FIG. 94A shows calorimetry data for the two doses of carbon
dioxide of Example 32, and uncarbonated control, power vs.
time.
[0111] FIG. 94B shows calorimetry data for the two doses of carbon
dioxide of Example 32, and uncarbonated control, energy vs.
time.
[0112] FIG. 95 shows calorimetry curves for 5 mortars with varying
levels of CO.sub.2 uptake (1 sample before carbonation followed by
5 rounds of carbonation, each for 2 min at 0.15 LPM) of Example
33.
[0113] FIG. 96 shows total energy released at 4 hours after mixing
for the 4 different levels of carbonation of Example 33, compared
to uncarbonated control.
[0114] FIG. 97 shows total energy released at 8 hours after mixing
for the 4 different levels of carbonation of Example 33, compared
to uncarbonated control.
[0115] FIG. 98 shows total energy released at 12 hours after mixing
for the 4 different levels of carbonation of Example 33, compared
to uncarbonated control.
[0116] FIG. 99 shows total energy released at 16 hours after mixing
for the 4 different levels of carbonation of Example 33, compared
to uncarbonated control.
[0117] FIG. 100 shows calorimetry as power vs. time for a mortar
mix made with carbonated mix water vs. uncarbonated mix water, as
described in Example 34.
[0118] FIG. 101 shows calorimetry as energy released vs. time for a
mortar mix made with carbonated mix water vs. uncarbonated mix
water, as described in Example 34.
[0119] FIG. 102 shows results for an Argos cement+Venture FA mix
under three different carbonation conditions, at three different
times, as total heat released relative to a control, uncarbonated
mix, as described in Example 35.
[0120] FIG. 103 results for a Cemex cement+Venture FA mix under
three different carbonation conditions, at three different times,
as total heat released relative to a control, uncarbonated mix, as
described in Example 35.
[0121] FIG. 104 shows results for a Holcim cement+Venture FA mix
under three different carbonation conditions, at three different
times, as total heat released relative to a control, uncarbonated
mix, as described in Example 35.
[0122] FIG. 105 shows results for a Titan Roanoake cement+Venture
FA mix under three different carbonation conditions, at three
different times, as total heat released relative to a control,
uncarbonated mix, as described in Example 35.
[0123] FIG. 106 shows results for an Argos cement+SEFA FA mix under
three different carbonation conditions, at three different times,
as total heat released relative to a control, uncarbonated mix, as
described in Example 35.
[0124] FIG. 107 shows results for a Cemex cement+SEFA FA mix under
three different carbonation conditions, at three different times,
as total heat released relative to a control, uncarbonated mix, as
described in Example 35.
[0125] FIG. 108 shows results for a Holcim cement+SEFA FA mix under
three different carbonation conditions, at three different times,
as total heat released relative to a control, uncarbonated mix, as
described in Example 35.
[0126] FIG. 109 shows results for a Titan Roanoake cement+SEFA FA
mix under three different carbonation conditions, at three
different times, as total heat released relative to a control,
uncarbonated mix, as described in Example 35.
[0127] FIG. 110 shows calorimetry as power vs. time for a mortar
mix made with a Roanoake cement-Trenton Class F fly ash 80/20
blend, carbonated for 2, 4, or 6 min, as described in Example
36.
[0128] FIG. 111 shows calorimetry as energy released vs. time for a
mortar mix made with a Roanoake cement-Trenton Class F fly ash
80/20 blend, carbonated for 2, 4, or 6 min, as described in Example
36.
[0129] FIG. 112 shows calorimetry as power vs. time for a mortar
mix made with a STMB cement-Trenton Class F fly ash 80/20 blend,
carbonated for 2, 4, or 6 min, as described in Example 36.
[0130] FIG. 113 shows calorimetry as energy released vs. time for a
mortar mix made with a STMB cement-Trenton Class F fly ash 80/20
blend, carbonated for 2, 4, or 6 min, as described in Example
36.
[0131] FIG. 114 shows calorimetry as power vs. time for a mortar
mix made with a STMB cement and three different doses of sodium
bicarbonate, as described in Example 37.
[0132] FIG. 115 shows calorimetry as energy released vs. time for a
mortar mix made with a STMB cement and three different doses of
sodium bicarbonate, as described in Example 37.
[0133] FIG. 116 shows calorimetry as power vs. time for a mortar
mix made with a LAFB cement and three different doses of sodium
bicarbonate, as described in Example 37.
[0134] FIG. 117 shows calorimetry as energy released vs. time for a
mortar mix made with a LAFB cement and three different doses of
sodium bicarbonate, as described in Example 37.
[0135] FIG. 118 shows calorimetry as power vs. time for a mortar
mix made with a STMB cement and two different times for addition of
carbonated mix water, as described in Example 38.
[0136] FIG. 119 shows calorimetry as energy released vs. time for a
mortar mix made with a STMB cement and two different times for
addition of carbonated mix water, as described in Example 38.
[0137] FIG. 120 shows calorimetry as power vs. time for a mortar
mix made with a LAFB cement and two different times for addition of
carbonated mix water, as described in Example 38.
[0138] FIG. 121 shows calorimetry as energy released vs. time for a
mortar mix made with a LAFB cement and two different times for
addition of carbonated mix water, as described in Example 38.
[0139] FIG. 122 shows calorimetry as power vs. time for a mortar
mix made with a LAFB cement and 5 different durations for addition
of carbonated mix water, as described in Example 38.
[0140] FIG. 123 shows calorimetry as energy released vs. time for a
mortar mix made with a LAFB cement and 5 different durations for
addition of carbonated mix water, as described in Example 38.
[0141] FIG. 124 shows calorimetry as power vs. time for a mortar
mix made with a STMB cement and a carbonated synthetic wash water,
filtered or unfiltered, as described in Example 39.
[0142] FIG. 125 shows calorimetry as energy released vs. time for a
mortar mix made with a STMB cement and a carbonated synthetic wash
water, filtered or unfiltered, as described in Example 39.
[0143] FIG. 126 shows calorimetry as power vs. time for a mortar
mix made with a LAFB cement and carbonated for 2, 4, or 6 minutes,
at 5 to 10.degree. C., as described in Example 40.
[0144] FIG. 127 shows calorimetry as energy released vs. time for a
mortar mix made with a LAFB cement and carbonated for 2, 4, or 6
minutes, at 5 to 10.degree. C., as described in Example 40.
[0145] FIG. 128 shows calorimetry as power vs. time for a mortar
mix made with a LAFB cement and carbonated for 2, 4, or 6 minutes,
at 10 to 15.degree. C., as described in Example 40.
[0146] FIG. 129 shows calorimetry as energy released vs. time for a
mortar mix made with a LAFB cement and carbonated for 2, 4, or 6
minutes, at 10 to 15.degree. C., as described in Example 40.
[0147] FIG. 130 shows calorimetry as power vs. time for a mortar
mix made with a STMB cement and carbonated for 2, 4, or 6 minutes,
at 5 to 10.degree. C., as described in Example 40.
[0148] FIG. 131 shows calorimetry as energy released vs. time for a
mortar mix made with a STMB cement and carbonated for 2, 4, or 6
minutes, at 5 to 10.degree. C., as described in Example 40.
[0149] FIG. 132 shows calorimetry as power vs. time for a mortar
mix made with a STMB cement and carbonated for 2, 4, or 6 minutes,
at 10 to 15.degree. C., as described in Example 40.
[0150] FIG. 133 shows calorimetry as energy released vs. time for a
mortar mix made with a STMB cement and carbonated for 2, 4, or 6
minutes, at 10 to 15.degree. C., as described in Example 40.
[0151] FIG. 134 shows the position at which the wand for carbon
dioxide delivery is aimed in the drum of a ready mix truck, at the
second fin in the truck on the bottom side of the drum.
[0152] FIG. 135 shows an extendable system for supplying carbon
dioxide, such as gaseous and solid carbon dioxide derived from
liquid carbon dioxide, to the drum of a ready mix truck, where the
system is attached to a flexible boot that delivers materials to
the drum of the truck.
[0153] FIG. 136 shows the system of FIG. 135 in retracted and
extended positions.
[0154] FIG. 137 shows an electron micrograph as described in
Example 41.
[0155] FIG. 138 shows pore silicon concentration in cement mixes
carbonated at different levels of carbonation at 8 minutes and 30
minutes after carbonation.
[0156] FIG. 139 shows power curves for the carbonated mixes of FIG.
138.
[0157] FIG. 140 shows the effect of carbonation on initial set in
cement mixes prepared with two different types of cement.
[0158] FIG. 141 shows the effect of carbonation on final set in
cement mixes prepared with two different types of cement.
[0159] FIG. 142 shows 24-hour compressive strength in carbonated
mortar mixes compared to control (uncarbonated) mortar mixes, where
the only binder was cement.
[0160] FIG. 143 shows 24-hour compressive strength in carbonated
mortar mixes compared to control (uncarbonated) mortar mixes, where
the binder was cement and class C fly ash.
[0161] FIG. 144 shows compressive strength results for 1, 3, 7, and
28 days for samples in 12 different industrial trials of
carbonation of concrete mixes.
[0162] FIG. 145 shows slump results for samples in 12 different
industrial trials of carbonation of concrete mixes.
[0163] FIG. 146 shows air results for samples in 12 different
industrial trials of carbonation of concrete mixes.
[0164] FIG. 147 provides a schematic illustration of a typical
volumetric concrete truck
DETAILED DESCRIPTION
I. Introduction
[0165] Carbon dioxide emissions are recognized as a significant
issue relating to cement production and the use of concrete as a
building material. It is estimated that 5% of the world's annual
CO.sub.2 emissions are attributable to cement production. The
industry has previously recognized a number of approaches to reduce
the emissions intensity of the cement produced and used. The most
significant improvements in efficiency and cement substitution are
likely to be already known and available. Future emissions
improvements will likely be incremental. Innovative approaches are
sought that can be a part of a portfolio strategy. Thus, a range of
further approaches will also have to be pursued.
[0166] One potential method is to up cycle captured carbon dioxide
into concrete products. The mechanism of the carbonation of freshly
hydrating cement was systematically studied in the 1970s at the
University of Illinois. The main cement phases, tricalcium silicate
and dicalcium silicate, were shown to react with carbon dioxide in
the presence of water to form calcium carbonate and calcium
silicate hydrate gel as shown in equations 1 and 2:
3CaO.SiO.sub.2+(3-x)CO.sub.2+yH.sub.2O.fwdarw.xCaO.SiO.sub.3.yH.sub.2O+(-
3-x)CaCO.sub.3 (1)
2CaO.SiO.sub.2+(2-x)CO.sub.2+yH.sub.2O.fwdarw.xCaO.SiO.sub.3.yH2O+(2-x)C-
aCO.sub.3 (2)
[0167] Further any free calcium hydroxide present in the cement
paste will rapidly hydrate and react with carbon dioxide, as show
in equation 3:
Ca(OH).sub.2+CO.sub.2+H.sub.2O.fwdarw.CaCO.sub.3+2H.sub.2O (3)
[0168] The carbonation reactions are exothermic. The reaction
proceeds in the aqueous state when Ca.sup.2+ ions from the
cementitious phases meet CO.sub.3.sup.2- ions from the applied gas.
The carbonation heats of reaction for the main calcium silicate
phases are 347 kJ/mol for C3S and 184 kJ/mol for .beta.-C2S and 74
kJ/mol for Ca(OH).sub.2.
[0169] When the calcium silicates carbonate, the calcium silicate
hydrate (C--S--H) gel that forms is understood to be intermixed
with CaCO.sub.3. C--S--H gel formation occurs even in an ideal case
of 13-C2S and C3S exposed to a 100% CO.sub.2 at 1 atm given the
observation that the amount of carbonate that forms does not
exactly correspond to the amount of calcium silicate involved in
the reaction.
[0170] The reaction of carbon dioxide with a mature concrete
microstructure is conventionally acknowledged to be a durability
issue due to such effects as shrinkage, reduced pore solution pH,
and carbonation induced corrosion. In contrast, a carbonation
reaction integrated into concrete production reacts CO.sub.2 with
freshly hydrating cement, rather than the hydration phases present
in mature concrete, and does not have the same effects. Rather, by
virtue of adding gaseous CO.sub.2 to freshly mixing concrete the
carbonate reaction products are anticipated to form in situ, be of
nano-scale and be homogenously distributed.
[0171] The invention provides methods, apparatus, and compositions
for production of materials comprising a cement binder, e.g., a
hydraulic cement or non-hydraulic cement. "Cement mix," as that
term is used herein, includes a mix of a cement binder, e.g., a
hydraulic cement, such as a Portland cement, and water; in some
cases, "cement mix" includes a cement binder mixed with aggregate,
such as a mortar (also termed a grout, depending on consistency),
in which the aggregate is fine aggregate; or "concrete," which
includes a coarse aggregate. The cement binder may be a hydraulic
or non-hydraulic cement, so long as it provides minerals, e.g.
calcium, magnesium, sodium, and/or potassium compounds such as CaO,
MgO, Na.sub.2O, and/or K.sub.2O that react with carbon dioxide to
produce stable or metastable products containing the carbon
dioxide, e.g., calcium carbonate. An exemplary hydraulic cement is
Portland cement. In general herein the invention includes
descriptions of hydraulic cement binder and hydraulic cement mixes,
but it will be appreciated that any cement mix is envisioned,
whether containing a hydraulic or non-hydraulic cement binder, so
long as the cement binder is capable of forming stable or
metastable products when exposed to carbon dioxide, e.g., contains
calcium, magnesium, sodium, and/or potassium compounds such as CaO,
MgO, Na.sub.2O, and/or K.sub.2O. In certain embodiments, the
invention provides methods, apparatus, and compositions for
production of a cement mix (concrete) containing cement, such as
Portland cement, treated with carbon dioxide. As used herein, the
term "carbon dioxide" refers to carbon dioxide in a gas, solid,
liquid, or supercritical state where the carbon dioxide is at a
concentration greater than its concentration in the atmosphere; it
will be appreciated that under ordinary conditions in the
production of cement mixes (concrete mixes) the mix is exposed to
atmospheric air, which contains minor amounts of carbon dioxide.
The present invention is directed to production of cement mixes
that are exposed to carbon dioxide at a concentration above
atmospheric concentrations.
[0172] Cement mix operations are commonly performed to provide
cement mixes (concrete) for use in a variety of applications, the
most common of which is as a building material. Such operations
include precast operations, in which a concrete structure is formed
in a mold from the cement mix and undergoes some degree of
hardening before transport and use at a location separate from the
mix location, and ready mix operations, in which the concrete
ingredients are supplied at one location and generally mixed in a
transportable mixer, such as the drum of a ready mix truck, and
transported to a second location, where the wet mix is used,
typically by being poured or pumped into a temporary mold. Precast
operations can be either a dry cast operation or a wet cast
operation, whereas ready mix operations are wet cast. Any other
operation in which a concrete mix is produced in a mixer and
exposed to carbon dioxide during mixing is also subject to the
methods and compositions of the invention.
[0173] Without being bound by theory, when the cement mix
(concrete) is exposed to carbon dioxide, the carbon dioxide first
dissolves in mix water and then forms intermediate species, before
precipitating as a stable or metastable species, e.g., calcium
carbonate. As the carbonate species are removed from solution,
further carbon dioxide may dissolve in the water. In certain
embodiments, the mix water contains carbon dioxide before exposure
to the cement binder. All of these processes are encompassed by the
term "carbonation" of the cement mix, as that term is used
herein.
II. Components
[0174] In certain embodiments the invention provides methods for
preparing a mix containing cement, by contacting a mixture of a
cement binder, e.g., hydraulic cement and water, and, optionally,
other components such as aggregate (a "cement mix", or "concrete,"
e.g., a "hydraulic cement mix") with carbon dioxide during some
part of the mixing of the cement mix, e.g., hydraulic cement
mix.
[0175] In certain embodiments, a hydraulic cement is used. The term
"hydraulic cement," as used herein, includes a composition which
sets and hardens after combining with water or a solution where the
solvent is water, e.g., an admixture solution. After hardening, the
compositions retain strength and stability even under water. An
important characteristic is that the hydrates formed from the
cement constituents upon reaction with water are essentially
insoluble in water. A hydraulic cement used may be any hydraulic
cement capable of forming reaction products with carbon dioxide.
The hydraulic cement most commonly used is based upon Portland
cement. Portland cement is made primarily from limestone, certain
clay minerals, and gypsum, in a high temperature process that
drives off carbon dioxide and chemically combines the primary
ingredients into new compounds. In certain embodiments, the
hydraulic cement in the hydraulic cement mix is partially or
completely composed of Portland cement.
[0176] A "hydraulic cement mix," as that term is used herein,
includes a mix that contains at least a hydraulic cement and water.
Additional components may be present, such as aggregates,
admixtures, and the like. In certain embodiments the hydraulic
cement mix is a concrete mix, i.e., a mixture of hydraulic cement,
such as Portland cement, water, and aggregate, optionally also
including an admixture.
[0177] The methods in certain embodiments are characterized by
contacting carbon dioxide with wet cement binder, e.g., hydraulic
cement, in a mixer at any stage of the mixing, such as during
mixing of the cement with water, or during the mixing of wetted
cement with other materials, or both. The cement may be any cement,
e.g., hydraulic cement capable of producing reaction products with
carbon dioxide. For example, in certain embodiments the cement
includes or is substantially all Portland cement, as that term is
understood in the art. The cement may be combined in the mixer with
other materials, such as aggregates, to form a cement-aggregate
mixture, such as mortar or concrete. The carbon dioxide may be
added before, during, or after the addition of the other materials
besides the cement and the water. In addition or alternatively, in
certain embodiments the water itself may be carbonated, i.e.,
contain dissolved carbon dioxide.
[0178] In certain embodiments, the contacting of the carbon dioxide
with the cement mix, e.g., hydraulic cement mix, may occur when
part but not all of the water has been added, or when part but not
all of the cement has been added, or both. For example, in one
embodiment, a first aliquot of water is added to the cement or
cement aggregate mixture, to produce a cement or cement-aggregate
mixture that contains water in a certain water/cement (w/c) ratio
or range of w/c ratios. In some cases one or more components of the
cement mix, e.g., hydraulic cement mix, such as aggregate, may be
wet enough that is supplies sufficient water so that the mix may be
contacted with carbon dioxide. Concurrent with, or after, the
addition of the water, carbon dioxide is introduced to the mixture,
while the mixture is mixing in a mixer.
[0179] The carbon dioxide may be of any purity and/or form suitable
for contact with cement, e.g., hydraulic cement during mixing to
form reaction products. As described, the carbon dioxide is at
least above the concentration of atmospheric carbon dioxide. For
example, the carbon dioxide may be liquid, gaseous, solid, or
supercritical, or any combination thereof. In certain embodiments,
the carbon dioxide is gaseous when contacted with the cement, e.g.,
hydraulic cement, though it may be stored prior to contact in any
convenient form, e.g., in liquid form. In alternative embodiments,
some or all of the carbon dioxide may be in liquid form and
delivered to the cement or cement mix (concrete), e.g., in such a
manner as to form a mixture of gaseous and solid carbon dioxide;
the stream of liquid carbon dioxide can be adjusted by, e.g., flow
rate and/or orifice selection so as to achieve a desired ratio of
gaseous to solid carbon dioxide, such as ratio of approximately
1:1, or within a range of ratios. The carbon dioxide may also be
solid when delivered to the concrete, i.e., as dry ice; this is
useful when a controlled or sustained release of carbon dioxide is
desired, for example, in a ready mix truck in transit to a mix
site, or other wet mix operations, as the dry ice sublimates over
time to deliver gaseous carbon dioxide to the mix; the size and
shape of the dry ice added to the mix may be manipulated to ensure
proper dose and time of delivery. In certain embodiments the carbon
dioxide is dissolved in water and delivered to the cement or cement
mix (concrete). The carbon dioxide may also be of any suitable
purity for contact with the cement or cement mix (concrete), e.g.,
hydraulic cement during mixing under the specified contact
conditions to form reaction products. In certain embodiments the
carbon dioxide is more than 5, 10, 20, 30, 40, 50, 60, 70, 80, 90,
95, or 99% pure. In certain embodiments, the carbon dioxide is more
than 95% pure. In certain embodiments, the carbon dioxide is more
than 99% pure. In certain embodiments, the carbon dioxide is
20-100% pure, or 30-100% pure, or 40-100% pure, or 50-100% pure, or
60-100% pure, or 70-100% pure, or 80-100% pure, or 90-100% pure, or
95-100% pure, or 98-100% pure, or 99-100% pure. In certain
embodiments, the carbon dioxide is 70-100% pure. In certain
embodiment, the carbon dioxide is 90-100% pure. In certain
embodiment, the carbon dioxide is 95-100% pure. The impurities in
the carbon dioxide may be any impurities that do not substantially
interfere with the reaction of the carbon dioxide with the wet
cement mix, e.g., hydraulic cement mix. Commercial sources of
carbon dioxide of suitable purity are well-known.
[0180] The carbon dioxide, e.g., carbon dioxide gas, liquid, or
solid, may be commercially supplied high purity carbon dioxide. In
this case, the commercial carbon dioxide, e.g., gas, liquid, or
solid, may be sourced from a supplier that processes spent flue
gasses or other waste carbon dioxide so that sequestering the
carbon dioxide in the cement mix, e.g., hydraulic cement mix
sequesters carbon dioxide that would otherwise be a greenhouse gas
emission.
[0181] In addition, because carbonation of a cement mix, e.g., a
concrete mix, often produces an improvement in strength compared to
uncarbonated mix, less cement can be used in the production of a
concrete that is equal in strength. In some cases, the amount of
carbon dioxide absorbed is modest but if a consistent strength
benefit can be realized then there is motivation to optimize the
process and reduce the cement content. For example, masonry
producers generally do not have any internal or external motivation
to produce product that has a strength 119% of the conventional
product. Instead, an economic gain can be realized by using a mix
design that contains less cement and achieves, through help of the
carbonation process, 100% of the uncarbonated product strength. A
reduced cement mix design would additionally have clear
environmental benefits given that Portland cement clinker typically
has embodied CO.sub.2 on the order of 866 kg CO.sub.2e/tonne of
clinker. If 5% of the cement was removed from the block mix design
(about 333 kg/m.sup.3) then the emissions savings would be around
14 kg/m.sup.3 concrete before including any net offset related to
the CO.sub.2 absorption. Thus, in certain embodiments, the
invention provides a carbonated concrete composition comprising an
amount of cement that is less than the amount of cement needed in
an uncarbonated concrete composition of the same or substantially
the same mix design, e.g., at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
12, 15, 17, 20, 25, 30, 40, or 50% less cement, but with a
strength, e.g., compressive strength, that is within 20, 15, 10, 5,
3, 2, or 1% of the compressive strength of the uncarbonated
concrete mix at a given time or times after mixing, such as 24
hours, 2 days, 7 days, 14 days, 21 days, 56 days, or 91 days, or a
combination thereof. These times are merely exemplary and any time
or combination of times that gives meaningful information about the
strength of the mix as related to its intended use may be used.
Such compositions realize a net savings in CO.sub.2 emissions that
includes the amount of carbon dioxide taken up by the composition,
and the amount of carbon dioxide emission avoided because less
cement is needed in the production of the composition. For example,
the net emission savings may be at least 1, 2, 3, 4, 5, 7, 10, 12,
15, 17, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 125, or
150 kg CO.sub.2/m.sup.3 of concrete for the carbonated compared to
the uncarbonated concrete. The concrete may be in the form of a
precast object, such as a block, pipe, brick, paver, or the like;
the concrete may be in the form of a ready-mix concrete that is
poured into molds at a job site. The carbonation of the concrete
may produce nanocrystals of calcium carbonate as described
elsewhere herein. Substantial cost savings can also be realized by
decreasing the amount of cement for a given concrete mix without
sacrificing strength.
[0182] The carbon dioxide is contacted with the cement mix, e.g.,
hydraulic cement mix during mixing by any suitable route, such as
over part or all of the surface of the mixing cement mix, e.g.,
hydraulic cement mix, under the surface of the cement mix, e.g.,
hydraulic cement mix, or any combination thereof. In certain
embodiments where concrete is mixed in a first container and then
introduced into a second container, such as at a ready-mix batching
facility where concrete is first mixed in a mixer then transferred
to the drum of a ready-mix truck, carbon dioxide is introduced into
the second container prior to pre-mixed concrete being introduced
into that container. Additionally or alternatively, the concrete
may be contacted with carbon dioxide as it is being transferred
from the first mix container to the second container. The carbon
dioxide may be in any form as described herein, e.g., gas, solid,
or a mix of gas and solid. In certain embodiments, the carbon
dioxide is introduced into the second container as a solid, or a
mixture of gas and solid; for example, the carbon dioxide may be
supplied in a conduit as liquid carbon dioxide and on exiting an
opening or orifice of the conduit, be converted to solid and
gaseous carbon dioxide, as described elsewhere herein; the stream
of gaseous and solid carbon dioxide may be directed to the second
container before introduction of the concrete, and/or directed to
the stream of concrete introduced into the second container. As it
is advantageous to have a greater amount of solid carbon dioxide to
avoid escape of gaseous carbon dioxide to the atmosphere,
conditions of the introduction may be adjusted to achieve a high
ratio of solid to gaseous carbon dioxide. Alternatively or
additionally, carbon dioxide may be introduced into the second
container as dry ice, as described elsewhere herein. The carbon
dioxide in the second container is then contacted with the
pre-mixed concrete as it is poured into the second container and as
the second container continues to mix the concrete.
[0183] For example, in a ready-mix operation, concrete is often
mixed in a mixer at the batching site and poured into the drums of
ready-mix trucks for transport to the job site. The concrete
continues to mix in the drum of the ready-mix truck. Carbon dioxide
can be introduced into the drum of the ready-mix truck, e.g., as
gaseous and solid carbon dioxide formed from liquid carbon dioxide,
or as solid dry ice, or a combination thereof, prior to the
concrete being poured from the mixer into the drum. Additionally or
alternatively, carbon dioxide may be directed to the stream of
concrete as it is being poured from the mixer to the drum. When the
carbon dioxide is a mixture of gas and solid, e.g., produced from a
liquid carbon dioxide, the stream of gas and solid may be directed
to contact the stream of concrete being poured from the mixer, as
well as entering the drum of the ready-mix truck. Thus the stream
of solid and gaseous carbon dioxide may be positioned in such a way
as to introduce carbon dioxide into the stream of concrete entering
the drum of the truck, and also to introduce carbon dioxide into
the drum itself. Carbon dioxide, e.g., solid carbon dioxide or a
mixture of solid and gaseous carbon dioxide, may also be introduced
into the drum of the truck prior to the pouring of the concrete
into the drum. It will be appreciated that any combination of the
above approaches may be used in order to contact the concrete in
the drum of the truck with carbon dioxide. Such approaches are
especially useful with low doses of carbon dioxide, such as doses
no greater than 2%, or no greater than 1.5%, or no greater than 1%
bwc, as described elsewhere herein.
[0184] In certain embodiments, the carbon dioxide is contacted with
the cement mix, e.g., hydraulic cement mix during mixing by contact
with the surface of the mixing cement mix, e.g., hydraulic cement
mix. Without being bound by theory, it is believed that the carbon
dioxide contacted with the surface of the cement mix, e.g.,
hydraulic cement mix dissolves and/or reacts in the water, and is
then subsumed beneath the surface by the mixing process, which then
exposes different cement mix, e.g., cement mix, to be contacted,
and that this process continues for as long as the wetted hydraulic
cement is exposed to the carbon dioxide. It will be appreciated
that the process of dissolution and/or reaction may continue after
the flow of carbon dioxide is halted, since carbon dioxide will
likely remain in the gas mixture in contact with the cement mix,
e.g., hydraulic cement mix. In embodiments in which liquid carbon
dioxide is used to produce gaseous and solid carbon dioxide, the
solid carbon dioxide will sublimate and continue to deliver gaseous
carbon dioxide to the cement mix, e.g., hydraulic cement mix after
the flow of liquid carbon dioxide has ceased. This is particularly
useful in ready mix truck operations, where there may be
insufficient time at the batching facility to allow uptake of the
desired amount of carbon dioxide; the use of liquid carbon dioxide
which converts to gaseous and solid carbon dioxide allow more
carbon dioxide to be delivered to the mix even after the truck
leaves the batching facility.
[0185] In particular, in a ready-mix operation, the concrete may be
mixed in a stationary mixer, then transferred to the drum of the
ready-mix truck, or the components of the concrete may be delivered
to the drum of the ready-mix truck and the mixing of the components
to provide concrete occurs in the drum. In the former case, carbon
dioxide may be delivered to the stationary mixer, and in such a
case, the delivery may be similar or identical to that used in,
e.g., a precast operation, i.e., carbon dioxide is delivered via a
conduit which opens to the mixer and delivers the carbon dioxide to
the surface of the mixing concrete. The carbon dioxide may be any
form as described herein; in certain embodiments, the carbon
dioxide is delivered as liquid which, upon exiting the opening of
the conduit, converts to a solid and a gas, as described herein.
Further carbonation of the concrete may be achieved, if desired, by
delivery of additional carbon dioxide to the drum of the ready mix
truck after the concrete is delivered to it. Alternatively, all
carbon dioxide may be delivered to the drum of the ready-mix truck;
this will clearly be the case if the mixing of the concrete occurs
in the drum. In this case, a delivery system for carbon dioxide to
the drum of the ready-mix truck is needed.
[0186] The carbon dioxide can be delivered after the components of
the concrete mix are placed in the drum; for example, in some
ready-mix operations, the truck is moved to a wash rack where it is
washed down prior to leaving the yard. When such a delivery system
is used, the positioning of the conduit for the carbon dioxide,
also referred to as a wand or lance herein, so that the opening is
in a certain position and attitude relative to the drum can be
important; one aspect of some embodiments of the invention is
positioning the wand, and/or apparatus for doing so, to facilitate
efficient mixing of the gaseous and solid carbon dioxide with the
cement mix as the drum rotates. Any suitable positioning method
and/or apparatus may be used to optimize the efficiency of uptake
of carbon dioxide into the mixing cement as long as it positions
the wand in a manner that provides efficient uptake of the carbon
dioxide, for example, by positioning the wand so that the opening
is directed to a point where a wave of concrete created by fins of
the ready mix drum folds over onto the mix; without being bound by
theory it is thought that the wave folding over the fin immediately
subsumes the solid carbon dioxide within the cement mix so that it
releases gaseous carbon dioxide by sublimation into the mix rather
than into the air, as it would do if on the surface of the mix. One
exemplary positioning is shown in FIG. 134, where the wand is aimed
at the second fin in the drum of the truck, on the bottom side of
the fin. In a ready mix truck carrying a full load, the opening of
the wand may be very close to the surface of the mixing concrete,
as described below, to facilitate the directional flow of the
carbon dioxide mix into the proper area. Part or all of the wand
may be made of flexible material so that if a fin or other part of
the drum hits the wand it flexes then returns to its original
position.
[0187] In certain embodiments, the invention provides a system for
positioning a carbon dioxide delivery conduit on a ready mix truck
so that the opening of the conduit is directed to a certain
position in the drum of the truck, for example, as described above.
The conduit may deliver gaseous carbon dioxide or a mixture of
gaseous and solid carbon dioxide through the opening. In the latter
case, the conduit is constructed of materials that can withstand
the liquid carbon dioxide carried by the conduit to the opening.
The system can include a guide, which may be mounted on the truck,
for example permanently mounted, or that may be part of the lance
assembly, that is configured to allow the reversible positioning of
the conduit, for example, by providing a cylinder or holster into
which the conduit can be inserted, so that the conduit is
positioned at the desired angle for delivery of the carbon dioxide
to a particular point, and a stop to ensure that the conduit is
inserted so that the opening is at the desired distance from the
concrete. This is merely exemplary and one of skill in the art will
recognize that any number of positioning devices may be used, so
long as the angle and position of the opening relative to a desired
point in the drum is obtained. The wand is positioned in the guide,
for example, manually by the driver, or automatically by an
automated system that senses the positions of the various
components. A sensor may be tripped when the wand is positioned
properly and a system controller may then begin carbon dioxide
delivery, either at that time or after a desired delay. The
controller can be configured so that if the conduit is not
positioned properly, e.g., the sensor does not send the signal, the
delivery will not start. The system may also be configured so that
if one or more events occur during before, during, or after
delivery, an alarm sounds and/or delivery is modulated, for
example, stopped, or not initiated. For example, an alarm can sound
if the wand loses signal from the positioning sensor during
injection, the pressure is greater than 25 psi when both valves for
delivery of gaseous and liquid carbon dioxide to the conduit is
closed, e.g., when both are closed (which determines if a valve
sticks open), or if the next truck in the queue has not been
initiated in a certain amount of time. Exemplary logic for a
controller can include:
[0188] If the wand loses signal during injection, an alarm light
comes on and a message can pop on a HMI, for example, a screen,
informing an operator that the injection wand is disconnected and
to reconnect and press Start button to continue. There can also be
an indicator, e.g., a button that indicates "Injection Complete"
which would end that batch and record what was actually injected vs
the target. In a batching facility in which a plurality of
different trucks are being batched, a system controller may be
configured to receive input regarding the identity of each truck at
the carbon dioxide delivery site and select the appropriate action,
e.g., delivery/no delivery, timing, flow, and amount of carbon
dioxide delivered, and the like. For example, for entering a truck
number that corresponds to the current truck being batched (signal
being sent to plc), a dialog box can pop up when the system
controller gets the signal from the customer PLC asking an operator
to "Please input Identification Number" (e.g., a 1-10 digit
number), alternatively, the truck identifier numbers can be in a
predetermined order, e.g., sequential. To choose the option, there
may be a selector switch on the maintenance screen. Feedback may
also be provided to an operator, e.g., a batcher, showing relevant
information for the batches run, such as Identification Number,
Time Batched, Time Injected, Dose Required and Dose Injected, and
the like. The units of the dose can be any suitable units, for
example either lbs or kgs depending on the units selected. A
"spreadsheet" can be provided that shows all batches from the
current day (or makes the date selectable) so that the batcher can
review it and scroll though, for example a printable
spreadsheet.
[0189] In certain embodiments, carbon dioxide is added to the drum
of a ready-mix truck while the truck is positioned to receive the
components of the concrete; this allows earlier contact of the
carbon dioxide with the concrete mix and also allows all
components--concrete and carbon dioxide--to be added at once,
avoiding the necessity for the truck operator to perform an
additional step to add the carbon dioxide. Generally, in an
operation where the components of the concrete are added to the
drum of the ready-mix truck for mixing, a flexible large conduit,
generally referred to as a loading boot, such as a rubber boot, is
positioned to direct materials (cement, aggregate, etc.) from
loading hopper/bin into the concrete truck chute; this system
minimizes spillage. See FIG. 135. In this case, a smaller conduit
for delivery of carbon dioxide can be positioned within the larger
conduit (boot) to move with the boot and be configured to direct
the carbon dioxide into the drum of the ready-mix truck. Thus, an
example another method and apparatus for positioning a wand for
delivery of carbon dioxide to a ready-mix truck is described in
Example 42 and FIGS. 135 and 136. In this system, a flexible hose
housed in a pipe, where the hose is extended through a loading boot
and into a concrete truck's chute by the action of an apparatus
suitable for extending the hose, such as a telescopic air cylinder
rod or a rotary device. One or more components of the apparatus may
be suitably configured to direct the carbon dioxide to a desired
location or area in the drum, such as by a bend in the
apparatus.
[0190] In embodiments in which carbon dioxide is directed as a
solid/gas mixture into a mixer, such as into a ready-mix truck or
into a stationary mixer, it may be desirable to modulate the flow,
e.g., slow the flow, so that the solid carbon dioxide particles can
clump together into larger particles before contacting the cement
mix, e.g., hydraulic cement mix such as concrete, in the mixer.
Without being bound by theory, it is thought that by allowing
larger conglomerations to form, the rate of sublimation is slowed
and the released gaseous carbon dioxide is more likely to be taken
up by the cement mix rather than escaping to the atmosphere.
[0191] One method modulating the flow of the solid/gas carbon
dioxide mixture is to expand the diameter of the conduit through
which the solid/gas mixture flows, and/or to introduce a bend into
the conduit. Both the increase in diameter and the bend in the
conduit serve to slow the velocity; however, in certain embodiments
only an increase in diameter is used; in certain embodiments, only
a bend is used. Any suitable step-up in size may be used, with or
without a bend, so long as the rate of flow of the gas/solid carbon
dioxide mix is slowed sufficiently to provide the desired clumping
of solid particles before contact with the cement mix; in general
it is preferred that the velocity remain high enough that the solid
carbon dioxide does not stick inside the conduit.
[0192] A larger diameter, with or without a bend, may also be used
for a conduit used to deliver a gas/solid mixture of carbon dioxide
to a non-stationary mixer, e.g., a ready-mix truck. The increase in
diameter of the conduit may be any increase that produces the
desired clumping of the solid carbon dioxide, preferably with no or
very little buildup of solid carbon dioxide in the conduit.
[0193] It will be appreciated that other systems of positioning a
conduit for delivery of carbon dioxide to a ready-mix truck may be
used, such as systems wherein the conduit, or lance, is attached to
a stand and is positioned into the drum of the truck without being
temporarily attached to the truck. Such systems are included in
embodiments of the invention. For descriptions of exemplary
systems, see, e.g., U.S. Patent Application Publication No.
2014/0216303, and U.S. Pat. No. 8,235,576.
[0194] In embodiments in which carbon dioxide is contacted with the
surface of the cement mix, e.g., hydraulic cement mix, the flow of
carbon dioxide may be directed from an opening or plurality of
openings (e.g., manifold or conduit opening) that is at least 5,
10, 20, 30, 40, 50, 60, 70, 80, 90, or 100 cm from the surface of
the cement mix, e.g., hydraulic cement mix during carbon dioxide
flow, on average, given that the surface of the mix will move with
mixing, and/or not more than 10, 20, 30, 40, 50, 60, 70, 80, 90,
100, 120, 140, 170, or 200 cm from the surface of the cement mix,
e.g., hydraulic cement mix during carbon dioxide flow, on average.
In certain embodiments, the opening is 5-100 cm from the surface,
on average, such as 5-60 cm, for example 5-40 cm.
[0195] Other methods of increasing carbon dioxide delivery, such as
using carbon dioxide-charged water in the mix, may also be used. In
addition, or alternatively, solid carbon dioxide, i.e., dry ice,
may be used directly by addition to the concrete mix. This allows
for controlled delivery as the dry ice sublimates, as described.
For example, dry ice may be added to a cement mix in a ready mix
truck. The amount of dry ice added may be enough to provide a dose
of 0.01-5% carbon dioxide bwc, for example, 0.01-1%, or 0.01-0.5%,
or 0.01-0.2%, or 0.1-2% or 0.1-1%, or 0.2-3%, or 0.5-3%. The dry
ice may be added in one or more batches. The shape of the dry ice
may be selected depending on, e.g., the speed of gaseous carbon
dioxide delivery desired; for example, if rapid delivery is
desired, the dry ice may be added as small pellets, thus increasing
surface/volume ratio for carbon dioxide sublimation, or if a slower
delivery is desired, the dry ice may be added as a larger mass,
e.g., slab, with a correspondingly smaller surface/volume ratio and
slower sublimation, or any combination of shapes and masses to
achieve the desired dose of carbon dioxide and rate of delivery.
The dry ice may be added at any convenient stage in mixing, for
example, at the start of mixing or within 5 or 10 minutes of the
start of mixing, or later in the mixing, for example, as a ready
mix truck approaches a job site or the time of delivery of its
concrete load. In addition, solid carbon dioxide may be added
before or after a first, second, or third addition of water where
water addition to the concrete mix is divided into two or more
doses. Mixing speed for the concrete mix may also be modulated to
achieve a desired rate of dosing or other desired results. For
example, in certain embodiments, the invention provides a method
for delivering carbon dioxide to concrete mixing in a ready mix
truck by adding solid carbon dioxide to the concrete mix during the
mixing, where at least 20, 30, 40, 50, 60, 70, 80, 90, 95, or 99%
of the carbon dioxide delivered to the concrete is added in the
form of solid carbon dioxide.
[0196] In embodiments in which the carbon dioxide is contacted
under the surface of the cement mix, e.g., hydraulic cement mix,
any suitable route of providing the carbon dioxide may be used. In
some embodiments, the flow of carbon dioxide may be both under the
surface and over the surface, either by use of two different
openings or plurality of openings or by movement of the openings
relative to the mix, e.g., under the surface at one stage and over
the surface at another, which may be useful to prevent clogging of
the openings.
[0197] The carbon dioxide may be contacted with the cement mix,
e.g., hydraulic cement mix such that it is present during mixing by
any suitable system or apparatus. In certain embodiments, gaseous
or liquid carbon dioxide is supplied via one or more conduits that
contain one or more openings positioned to supply the carbon
dioxide to the surface of the mixing cement mix, e.g., hydraulic
cement mix. The conduit and opening may be as simple as a tube,
e.g., a flexible tube with an open end. The conduit may be
sufficiently flexible so as to allow for movement of various
components of the cement mix, e.g., hydraulic cement mixing
apparatus, the conduit opening, and the like, and/or sufficiently
flexible to be added to an existing system as a retrofit. On the
other hand, the conduit may be sufficiently rigid, or tied-off, or
both, to insure that it does not interfere with any moving part of
the cement mix, e.g., hydraulic cement mixing apparatus. In certain
embodiments, part of the conduit can be used for supplying other
ingredients to the cement mix, e.g., water, and configured such
that either the other ingredient or carbon dioxide flows through
the conduit, e.g., by a T-junction.
[0198] In certain embodiments, the carbon dioxide exits the conduit
or conduits via one or more manifolds comprising a plurality of
openings. The opening or openings may be positioned to reduce or
eliminate clogging of the opening with the cement mix, e.g.,
hydraulic cement mix. The manifold is generally connected via the
conduit to at least one fluid (gas or liquid) supply valve, which
governs flow of pressurized fluid between a carbon dioxide source,
e.g. a pressurized gas or liquid supply, and the manifold. In some
embodiments, the fluid supply valve may include one or more gate
valves that permit the incorporation of calibration equipment,
e.g., one or more mass flow meters.
[0199] The mass of carbon dioxide provided to the cement mix, e.g.,
hydraulic cement mix via the conduit or conduits may be controlled
by a mass flow controller, which can modulate the fluid supply
valve, e.g., close the valve to cease supply of carbon dioxide
fluid (liquid or gas).
[0200] Carbon dioxide may also be delivered to the cement mix,
e.g., hydraulic cement mix as part of the mix water, i.e.,
dissolved in some or all of the mix water. Methods of charging
water with carbon dioxide are well-known, such as the use of
technology available in the soda industry. Some or all of the
carbon dioxide to be used may be delivered this way. The mix water
may be charged to any desired concentration of carbon dioxide
achievable with the available technology, such as at least 1, 2, 4,
6, 8, 10, 12, 14, or 16 g of carbon dioxide/L of water, and/or not
more than 2, 4, 6, 8, 10, 12, 14, 18, 20, 22, or 24 g of carbon
dioxide/L of water, for example 1-12, 2-12, 1-10, 2-10, 4-12, 4-10,
6-12, 6-10, 8-12, or 8-10 g of carbon dioxide/L of water. It will
be appreciated that the amount of carbon dioxide dissolved in the
mix water is a function of the pressure of the carbon dioxide and
the temperature of the mix water; at lower temperatures, far more
carbon dioxide can be dissolved than at higher temperatures.
Without being bound by theory, it is thought that the mix water so
charged contacts the cement mix, e.g., hydraulic cement mix and the
carbon dioxide contained therein reacts very quickly with
components of the cement mix, e.g., hydraulic cement mix, leaving
the water available to dissolve additional carbon dioxide that may
be added to the system, e.g., in gaseous form.
[0201] In certain embodiments, a cement mix such as a concrete mix
is carbonated with carbon dioxide supplied as carbonated water, for
example, in the drum of a ready mix truck. The carbonated water
serves as a portion of the total mix water for the particular mix.
The carbonated water can provide at least 1, 5, 10, 15, 20, 25, 30,
35, 40, 50, 60, 70, 80, or 90% of the total mix water, and/or no
more than 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, or 100% of the
mix water. The carbonated water may be added at the start of mixing
of the cement mix, or it may be added after the start of mixing,
i.e., after a first addition of water to wet the cement mix. It can
be added as one batch or in stages, for example, as 2, 3, 4, 5 or
more than 5 batches. The batches may be equal in volume or
different volumes, and have the same carbonation or different
carbonations. In certain embodiments, the carbonated water is less
than 100% of the total mix water, for example, less than 80%, or
less than 70%, or less than 60%, or less than 50%. In certain of
these embodiments, embodiments, non-carbonated water is first added
to the mix, and the cement mix, e.g., concrete, is allowed to mix
for a certain period before carbonated water is added, for example,
for at least 5, 10, 15, 20, 30, 40, or 50 seconds, or at least 1,
2, 3, 4, 5, 6, 8, 10, 15, 20, 25, 30, 40, 50, or 60 minutes before
addition of the carbonated water, and/or not more than 10, 15, 20,
30, 40, or 50 seconds, or 1, 2, 3, 4, 5, 6, 8, 10, 15, 20, 25, 30,
40, 50, 60, 90, 120, 240, or 360 minutes before addition of
carbonated water. In certain embodiments, the delay before
carbonated water is added to the mix is between 10 seconds and 5
minutes, for example, between 20 seconds and 40 minutes, such as
between 30 seconds and 3 minutes. See Example 38. The flow rate of
the carbonated water may be adjusted so that a certain duration is
required for complete addition, such as a duration of at least 10,
20, 30, 40, or 50 seconds, or at least 1, 2, 3, 4, 5, 6, 7, 8, 9,
10, 12, 15, 20, or 30 minutes, and/or not more than 10, 20, 30, 40,
or 50 seconds, or not more than 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12,
15, 20, or 30 minutes. In certain embodiments, the duration of
addition of carbonated water is between 30 seconds and 8 minutes,
for example, between 30 seconds and 6 minutes, such as between 30
second and 4 minutes. See Example 38. The carbonated water may
contribute all of the carbon dioxide used to carbonate a cement
mix, e.g., concrete (neglecting atmospheric carbon dioxide); this
is especially true for low-dose carbonation, for example,
carbonation with a dose of carbon dioxide of less than 1.5% bwc, or
less than 1.0% bwc, or less than 0.8% bwc. The carbonated water may
contribute part or all of the carbon dioxide used to carbonate a
cement mix, e.g., concrete, such as not more than 10, 20, 30, 40,
50, 60, 70, 80, 90, 95, or 100% of the carbon dioxide and/or at
least 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 95% of the carbon
dioxide. In certain embodiments, the remaining carbon dioxide is
supplied as a gas. In certain embodiments, the remaining carbon
dioxide is supplied as a solid. In certain embodiments, the
remaining carbon dioxide is supplied as a mixture of a gas and a
solid, for example, carbon dioxide delivered to an orifice directed
into the mixer in liquid form, which becomes gas and solid when
passing through the orifice. The exact mix of carbonated water and
other carbon dioxide source will be determined based on the dose of
carbon dioxide to be delivered and other factors, such as delivery
time, temperature (lower temperatures allow greater carbon dioxide
delivery via carbonated water), and the like. The carbonated water
may be produced by any suitable method, as described herein, and
may be delivered to the mixer, e.g., the ready mix truck, via the
normal water line or via a dedicated line. In certain embodiments,
some or all of the carbonated water is produced from process water
that is produced during, e.g., a ready mix operation, such as
carbonated wash water that has been filtered, or unfiltered
carbonated wash water, or a combination thereof. The wash water may
be carbonated by any suitable method. See Example 39. The
carbonated wash water can provide at least 1, 5, 10, 15, 20, 25,
30, 35, 40, 50, 60, 70, 80, or 90% of the total carbonated mix
water, and/or no more than 10, 20, 30, 40, 50, 60, 70, 80, 90, 95,
or 100% of the total carbonated mix water. In certain embodiments
carbonated water is delivered to the mix at the batch site and/or
during transportation, and an optional dose is delivered at the job
site, depending on the characteristics of the mix measured at the
job site. The use of carbonated water can allow for very high
efficiencies of carbon dioxide uptake, as well as precise control
of dosage, so that highly efficient and reproducible carbon dioxide
dosing can be achieved. In certain embodiments in which carbonated
mix water is used, the efficiency of carbonation can be greater
than 60, 70, 80, 90, or even 95%, even when operating in mixers,
such as ready mix drums, which are open to the atmosphere.
[0202] The carbon dioxide is supplied from a source of carbon
dioxide, such as, in the case of gaseous carbon dioxide, a
pressurized tank filled with carbon dioxide-rich gas, and a
pressure regulator. The tank may be re-filled when near empty, or
kept filled by a compressor. The regulator may reduce the pressure
in the tank to a maximum feed pressure. The maximum feed pressure
may be above atmospheric, but below supercritical gas flow
pressure. The feed pressure may be, for example, in a range from
120 to 875 kPa. A pressure relief valve may be added to protect the
carbon dioxide source components. The carbon dioxide supplied by
the carbon dioxide source may be about room temperature, or it may
be chilled or heated as desired. In certain embodiments, some or
all of the carbon dioxide is supplied as a liquid. In some cases
the liquid is converted to gas before delivery to the mixer; in
other cases, the remains a liquid in storage and movement to the
mixer, and when released at the mixer forms a mixture comprising
solid and gaseous carbon dioxide. In the latter case, one or more
pressure sensors may be used; e.g., for the nozzle system to
control dry ice formation between the nozzle and solenoid as well
as to confirm pre-solenoid pressure is maintained to ensure the
line remains liquid.
[0203] Carbon dioxide may be introduced to the mixer such that it
contacts the hydraulic cement mix before, during, or after addition
of water, or any combination thereof, so long as it is present
during some portion of the mixing of some or all of the cement mix,
e.g., hydraulic cement mix. In certain embodiments, the carbon
dioxide is introduced during a certain stage or stages of mixing.
In certain embodiments, the carbon dioxide is introduced to a
cement mix, e.g., hydraulic cement mix during mixing at one stage
only. In certain embodiments, the carbon dioxide is introduced
during one stage of water addition, followed by a second stage of
water addition. In certain embodiments, the carbon dioxide is
introduced to one portion of cement mix, e.g., hydraulic cement
mix, followed by addition of one or more additional portions of
cement mix, e.g., hydraulic cement mix.
[0204] In certain embodiments, the carbon dioxide is introduced
into a first stage of mixing of water in the cement mix, e.g.,
hydraulic cement mix, then, after this stage, additional water is
added without carbon dioxide. For example, water may be added to a
cement mix, e.g., hydraulic cement mix, e.g., a Portland cement
mix, until a desired w/c ratio is achieved, then carbon dioxide may
be contacted during mixing of the cement mix, e.g., hydraulic
cement mix for a certain time at a certain flow rate or rates (or
as directed by feedback, described further herein), then after
carbon dioxide flow has stopped, additional water may be added in
one or more additional stages to reach a desired w/c content, or a
desired flowability, in the cement mix, e.g., hydraulic cement mix.
The cement mixes contain aggregates, and it will be appreciated
that the available aggregate may already have a certain water
content and that little or no additional water need be added to
achieve the desired w/c ratio for the first stage and that, in some
environments, it may not be possible to achieve the desired w/c
ratio because aggregate may be too wet, in which case the closest
w/c ratio to the optimum is achieved. In certain embodiments, the
w/c ratio for the first stage is less than 0.5, or less than 0.4,
or less than 0.3, or less than 0.2, or less than 0.18, or less than
0.16, or less than 0.14, or less than 0.12, or less than 0.10, or
less than 0.08, or less than 0.06. In certain embodiments, the w/c
ratio for the first stage is less than 0.4. In certain embodiments,
the w/c ratio for the first stage is less than 0.3. In certain
embodiments, the w/c ratio for the first stage is less than 0.2. In
certain embodiments, the w/c ratio for the first stage is less than
0.18. In certain embodiments, the w/c ratio for the first stage is
less than 0.14. In certain embodiments, the w/c ratio for the first
stage is 0.04-0.5, or 0.04-0.4, or 0.04-0.3, or 0.04-0.2, or
0.04-0.18, or 0.04-0.16, or 0.04-0.14, or 0.04-0.12, or 0.04-0.10,
or 0.04-0.08. In certain embodiments, the w/c ratio for the first
stage is 0.06-0.5, or 0.06-0.4, or 0.06-0.3, or 0.06-0.24, or
0.06-0.22, or 0.06-0.2, or 0.06-0.18, or 0.06-0.16, or 0.06-0.14,
or 0.06-0.12, or 0.06-0.10, or 0.06-0.08. In certain embodiments,
the w/c ratio for the first stage is 0.08-0.5, or 0.08-0.4, or
0.08-0.3, or 0.08-0.24, or 0.08-0.22, or 0.08-0.2, or 0.08-0.18, or
0.08-0.16, or 0.08-0.14, or 0.08-0.12, or 0.08-0.10. In certain
embodiments, the w/c ratio for the first stage is 0.06-0.3. In
certain embodiments, the w/c ratio for the first stage is 0.06-0.2.
In certain embodiments, the w/c ratio for the first stage is
0.08-0.2. Addition of additional water in subsequent stages to the
first stage, when, in general, no further carbon dioxide is
introduced, may be done to achieve a certain final w/c ratio, or to
achieve a certain flowability. For example, for a ready-mix truck,
a certain amount of water is added to the mixture at the ready-mix
production site, then further water may be added at the work site
to achieve proper flowability at the work site. Flowability may be
measured by any suitable method, for example, the well-known slump
test.
[0205] In some embodiments, carbon dioxide is added during mixing
to a portion of a cement mix, e.g., hydraulic cement mix in one
stage, then additional portions of materials, e.g., further cement
mix, e.g., hydraulic cement mix, are added in one or more
additional stages.
[0206] The carbon dioxide, e.g., gaseous carbon dioxide or liquid
carbon dioxide, is introduced in the mixing cement mix, e.g.,
hydraulic cement mix, for example, in the first stage of mixing, at
a certain flow rate and for a certain duration in order to achieve
a total carbon dioxide exposure. The flow rate and duration will
depend on, e.g., the purity of the carbon dioxide gas, the total
batch size for the cement mix, e.g., hydraulic cement mix and the
desired level of carbonation of the mix. A metering system and
adjustable valve or valves in the one or more conduits may be used
to monitor and adjust flow rates. In some cases, the duration of
carbon dioxide flow to provide exposure is at or below a maximum
time, such as at or below 100, 50, 20, 15, 10, 8, 5, 4, 3, 2, or
one minute. In certain embodiments, the duration of carbon dioxide
flow is less than or equal to 5 minutes. In certain embodiments,
the duration of carbon dioxide flow is less than or equal to 4
minutes. In certain embodiments, the duration of carbon dioxide
flow is less than or equal to 3 minutes. In certain embodiments,
the duration of carbon dioxide flow is less than or equal to 2
minutes. In certain embodiments, the duration of carbon dioxide
flow is less than or equal to 1 minutes. In some cases, the
duration of carbon dioxide flow to provide exposure is within a
range of times, such as 0.5-20 min, or 0.5-15 min, or 0.5-10 min,
or 0.5-8 min, or 0.5-5 min, or 0.5-4 min, or 0.5-3 min, or 0.5-2
min, or 0.5-1 min, or 1-20 min, or 1-15 min, or 1-10 min, or 1-8
min, or 1-5 min, or 1-4 min, or 1-3 min, or 1-2 min. In certain
embodiments, the duration of carbon dioxide flow is 0.5-5 min. In
certain embodiments, the duration of carbon dioxide flow is 0.5-4
min. In certain embodiments, the duration of carbon dioxide flow is
0.5-3 min. In certain embodiments, the duration of carbon dioxide
flow is 1-5 min. In certain embodiments, the duration of carbon
dioxide flow is 1-4 min. In certain embodiments, the duration of
carbon dioxide flow is 1-3 min. In certain embodiments, the
duration of carbon dioxide flow is 1-2 min.
[0207] The flow rate and duration of flow may be set or adjusted to
achieve a desired level of carbonation, as measured by weight of
cement (bwc). It will be appreciated that the precise level of
carbonation will depend on the characteristics of a given mix and
mix operation. In certain embodiments, the level of carbonation is
more than 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10% bwc. In certain
embodiments, the level of carbonation is more than 1% by weight. In
certain embodiments, the level of carbonation is more than 2% bwc.
In certain embodiments, the level of carbonation is more than 3%
bwc. In certain embodiments, the level of carbonation is more than
4% bwc. In certain embodiments, the level of carbonation is more
than 5% bwc. In certain embodiments, the level of carbonation is
more than 6% bwc. In certain embodiments, the level of carbonation
is 1-20%, or 1-15%, or 1-10%, or 1-8%, or 1-6%, or 1-5%, or 1-4%,
or 1-3%, or 1-2%, or 2-20%, or 2-15%, or 2-10%, or 2-8%, or 2-6%,
or 2-5%, or 2-4%, or 2-3%, or 0.5-20%, or 0.5-15%, or 0.5-10%, or
0.5-8%, or 0.5-6%, or 0.5-5%, or 0.5-4%, or 0.5-3%, or 0.5-2%. In
certain embodiments, the level of carbonation is 0.5-3%. In certain
embodiments, the level of carbonation is 0.5-2%. In certain
embodiments, the level of carbonation is 1-6%. In certain
embodiments, the level of carbonation is 1-4%. In certain
embodiments, the level of carbonation is 2-8%. In certain
embodiments, the level of carbonation is 2-6%. In certain
embodiments, the level of carbonation is 2-4%. In certain
embodiments, the level of carbonation is 3-10%. In certain
embodiments, the level of carbonation is 3-8%. In certain
embodiments, the level of carbonation is 3-6%. In certain
embodiments, the level of carbonation is 4-10%. In certain
embodiments, the level of carbonation is 4-8%. In certain
embodiments, the level of carbonation is 4-6%. In certain
embodiments, the level of carbonation is 5-10%. In certain
embodiments, the level of carbonation is 5-8%. In certain
embodiments, the level of carbonation is 5-6%. The level of
carbonation may be ascertained by any suitable method, such as by
the standard combustion analysis method, e.g. heating sample and
quantifying the composition of the off gas. An instrument such as
the Eltra CS-800 (KR Analytical, Cheshire, UK), or instrument from
LECO (LECO Corporation, St. Joseph, Mich.) may be used.
[0208] It will be appreciated that the level of carbonation also
depends on the efficiency of carbonation, and that inevitably some
of the carbon dioxide delivered to the mixing cement mix will be
lost to the atmosphere; thus, the actual amount of carbon dioxide
delivered can be adjusted based on the expected efficiency of
carbonation. Thus for all the desired levels of carbonation as
listed, an appropriate factor may be added to determine the amount
of carbon dioxide that is to be delivered as a dose to the cement
mix; e.g., if the expected efficiency is 50% and the desired
carbonation level is 1% bwc, then a dose of 2% bwc would be
delivered to the mix. Appropriate doses may be calculated for
desired carbonations at an efficiency of 5, 10, 20, 30, 40, 50, 60,
65, 70, 75, 80, 85, 90, 95, 96, 97, 98, or 99%.
Low Dose Carbonation
[0209] In certain embodiments, a relatively low level of
carbonation is used, e.g., a level of carbonation below 1%, 0.8%,
0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, or 0.05% bwc. It has been
found that certain properties, e.g., early strength development and
set, may be accelerated in cement mixes, such as hydraulic cement
mixes, that are exposed to relatively low levels of carbon dioxide
during mixing. It is possible that, in some cases, the exposure may
be low enough that the degree of carbonation is not measurably
above that of a similar cement mix that has not been exposed to
carbon dioxide; nonetheless, the exposure may lead to the desired
enhanced properties. Thus, in certain embodiments, the mixing
cement mix is exposed to a certain relatively low dose of carbon
dioxide (in some cases regardless of final carbonation value); in
this sense, carbon dioxide is used like an admixture whose final
concentration in the cement mix is not important but rather its
effects on the properties of the mix. In certain embodiments, the
mix may be exposed to a dose of carbon dioxide of not more than
1.5%, 1.2%, 1%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, or
0.05% bwc and/or at least 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6,
0.7, 0.8, 0.9, 1.0, or 1.2% bwc, such as a dose of 0.01-1.5%,
0.01-1.2%, 0.01-1%, 0.01-0.8%, 0.01-0.6%, 0.01-0.5%, 0.01-0.4%,
0.01-0.3%, 0.01-0.2%, or 0.01-0.1% bwc, or a dose of 0.02-1.5%,
0.02-1.2%, 0.02-1%, 0.02-0.8%, 0.02-0.6%, 0.02-0.5%, 0.02-0.4%,
0.02-0.3%, 0.02-0.2%, or 0.02-0.1% bwc, or a dose of 0.04-1.5%,
0.04-1.2%, 0.04-1%, 0.04-0.8%, 0.04-0.6%, 0.04-0.5%, 0.04-0.4%,
0.04-0.3%, 0.04-0.2%, or 0.04-0.1% bwc, or a dose of 0.06-1.5%,
0.06-1.2%, 0.06-1%, 0.06-0.8%, 0.06-0.6%, 0.06-0.5%, 0.06-0.4%,
0.06-0.3%, 0.06-0.2%, or 0.06-0.1% bwc, or a dose of 0.1-1.5%,
0.1-1.2%, 0.1-1%, 0.1-0.8%, 0.1-0.6%, 0.1-0.5%, 0.1-0.4%, 0.1-0.3%,
or 0.1-0.2% bwc. The choice of exposure level will depend on
factors such as efficiency of carbonation in the process being
used, degree of modulation of one or more properties desired (e.g.,
early strength development or early set), type of operation (e.g.,
dry cast vs. wet cast), and type of cement, as different types of
cement may produce mixes with different degrees of modulation with
a given carbon dioxide exposure. If an unfamiliar cement or mix
type is being used, preliminary work may be done to find one or
more suitable carbon dioxide doses to produce the desired results.
Especially in the case of accelerated strength and/or set
development, the use of an appropriate dose of carbon dioxide can
allow work to progress faster, e.g., vertical pours may move upward
more quickly, surfaces may be finished earlier, molds removed
earlier, and the like.
Tailoring Carbonation to Mix and Conditions at Site
[0210] In all dosing settings, for example, in low dose, the dose
chosen for a given mix as well as dosing conditions, for example,
to produce a desired increase in early strength or set, or to
produce an optimal increase in early strength or set, can be
dependent on the mix and especially on the cement used in the mix,
as well as conditions in the field where dosing and use actually
occur. Cements used in mixes are generally produced locally and
vary from one geographic location to another, and the particular
chemistry of a cement can determine whether or not it will benefit
from carbonation, as well as optimal dosing parameters, such as
overall dose, time to add carbon dioxide, rate of addition, and the
like. Other components of a particular mix, e.g. SCMs such as fly
ash or slag, may also provide one or more reactive species that
also influence carbonation. See, e.g., Example 45.
[0211] In certain embodiments, the invention provides methods for
determining whether or not to carbonate a given cement mix, and/or
to determine a level of carbonation and/or dose of carbon dioxide
and/or dosing conditions to achieve a desired result from
carbonation of a cement mix, e.g., early strength development, or
strength development in a particular time frame, reduced amount of
cement required, or the like. The determination may be made by
predictions for a given mix, e.g., based on the chemistry of the
components, or testing, or a combination thereof. In testing, any
suitable characteristic or combination of characteristics may be
monitored in the testing, such as strength, flowability, and other
characteristics that are important for the particular batch design
being tested. In certain embodiments the invention provides a
method of carbonating a cement mix, e.g., concrete, during mixing,
where carbon dioxide is added to the mix at a certain dose or range
of doses, where the certain dose or range of doses is determined by
testing one or more components of the mix, for example, the
concrete, to determine a dose or a range of doses that produces
optimal or desired increase in early strength and/or set.
[0212] The composition of the cement mix for testing can be any
suitable composition, for example, as simple as cement and water,
or a mortar also including fine aggregate, e.g., sand, as well as
optional additional components, such as admixtures and the like.
See Examples for compositions used in testing. In certain
embodiments the concrete mix to be used in a given operation is
tested.
[0213] Carbonation of the test cement mix can be achieved by any of
the methods described herein, for example by delivery of carbon
dioxide to the cement mix under controlled conditions to achieve a
certain dose of carbon dioxide to the mix. In certain embodiments,
the carbonation is achieved by using a bicarbonate solution, rather
than carbon dioxide. It is thought that essentially all of the
bicarbonate delivered to a concrete mix will be converted to
carbonate so it is possible to control the exact level of
carbonation of the mix achieved, and thus to first determine a
desired level of carbonation, e.g., by testing a plurality of
levels of carbonation to find the level or range of levels that
produces the desired effect or effects. See, e.g., Example 37.
[0214] No matter what method of carbonation is used, if pre-testing
is used to determine a dose or range of doses, in general a
plurality of tests is conducted, i.e., using at least two, or at
least three, or at least four different doses of carbon dioxide.
For low-dose carbon dioxide delivery, the doses may all be below
1.5%, or 1.2%, or 1.0%, or 0.8%, or 0.6% carbon dioxide bwc. A dose
or range of doses to be used in the field is determined from one or
more test results from the test mixes, for example, calorimetry
results, as described herein, and/or compressive strength results,
and/or set results, and/or slump results. Methods of measuring
strength, set, slump, and other characteristics of concrete mixes
are well-known in the art and described, e.g., in the appropriate
ASTM testing protocols. In certain embodiments, the test mix
comprises the type of cement to be used in the concrete mix, and
water; additional components may include one or more aggregates,
admixtures, SCM, and any other suitable component, for example, as
will be used in the concrete mix; generally, components are used at
or near the proportion that will be used in the concrete mix. In
certain embodiments, the test mix comprises all the components to
be used in the concrete mix, in the same proportions as will be
used.
[0215] The focus can then shift to consistently achieving the
desired level of carbonation under the conditions in which the
carbon dioxide will actually be delivered to the cement mix to be
used in the field. For example, in a ready mix operation, a certain
efficiency may be achieved, e.g., by using techniques described
herein, so that the dose of carbon dioxide actually delivered may
be adjusted according to the efficiency of carbonation. Factors
such as the likely temperature at the batching facility and/or job
site can also affect carbonation and can also be taken into
account. See Example 40. It will be appreciated that the methods
and composition of the invention can be used to allow concrete
mixes to be used at temperatures lower than they would otherwise be
able to be used by virtue of the effects of carbonation on early
strength development, for example, at a temperature at least 1, 2,
3, 4, 5, 6, 7, 8, 9, or 10.degree. C. below the temperature at
which a non-carbonated mix of the same or substantially the same
design could be used.
[0216] Other factors that can affect efficiency of carbonation
and/or the effect of carbonates can include factors such as shear
rate of mixing, timing after water is added to the mix at which the
carbon dioxide is added to the mix, e.g., delayed addition, and
temperature as described above. Without being bound by theory, it
is thought that these factors can affect the formation of
nano-sized calcium carbonate, which can in turn affect the
resulting influence of calcium carbonate formation on, e.g.,
strength development and/or other characteristics of the cement
mix. A high shear rate can prevent aggregation of particles and
thus promotes formation of nanoparticles. Delaying addition of
carbon dioxide can allow calcium to come into solution and allow
solution chemistry to develop.
[0217] In certain embodiments, the invention provides methods for
determining whether or not to carbonate a given cement mix, and/or
to determine a level of carbonation and/or dose of carbon dioxide
and/or dosing conditions to achieve a desired result from
carbonation of a cement mix, e.g., early strength development, or
strength development in a particular time frame, or reduced amount
of cement needed in the mix, or the like. is determined, in whole
or in part, from the chemistry of the cement to be used in the
cement mix. In certain embodiments, one or more of free CaO, total
CaO, alkali content, loss on ignition, one or more oxides, ratio of
calcium to silica, fineness, iron content, or combinations thereof
can be used to determine a dose or range of doses for carbonation,
and/or dosing conditions for a particular cement mix.
[0218] It will be appreciated that, in the case of low dose
carbonation, a carbonation value may not be able to be determined,
and that in all cases strength tests can require multiple samples
and days to weeks to complete. Thus in some embodiments, a
predetermined dose of carbon dioxide is determined using an
alternative marker, such as isothermal calorimetry. Heat release
during hydration is related to two somewhat overlapping peaks. The
main heat release is related to the hydration of silicates, while a
second heat release, observed as a hump on the downslope of the
silicate peak, is associated with the hydration of the aluminates.
Isothermal calorimetry testing is easy to carry out in mortar or
even cement paste with very minimal sample preparation compared to
the making of concrete samples, thus allowing for a rapid and
convenient method of determining an optimal CO.sub.2 dose and
timing for a given cement, by testing a range of doses and delivery
times. The results obtained are either in the form of heat flow
rate over time (also referred to as power vs. time herein), which
describes the rate of cement hydration, or in the form of heat of
hydration over time, which is the integrated heat flow rate (also
referred to as energy vs. time herein). See, e.g., Example 30,
which describes several different doses of carbon dioxide added to
concrete in the drum of a ready mix truck, in trials conducted on
two separate days. FIGS. 81-85 show the absolute and relative
compressive strengths of samples from the different doses of carbon
dioxide, at different time points, for the first day; it can be
seen that as carbon dioxide dose increased, strength at all time
points generally increased. The isothermal calorimetry curves shown
in FIGS. 86A and 86B mirror this, with the highest dose of carbon
dioxide causing the greatest shift in the curve, and second and
third highest doses giving the second and third greatest shifts in
the curves. Similar results can be seen in other Examples, e.g.,
Example 30 and others.
[0219] Cements that are suitable for carbonation--with respect to
accelerated set and/or early strength development--can be readily
identified, and/or a dose or doses selected, as well as time of
dosing, from the isocalorimetry curves using any suitable
procedure, such as a procedure in which a cement paste, mortar, or
concrete is produced using the cement being tested. Admixtures may
also be tested, either separately or as part of an overall
protocol, to determine their effects on workability and other
desired characteristics, as well as optimal doses.
[0220] An exemplary procedure is as follows: [0221] 1. Prepare a
"control-control" sample with no carbonation and no admixture.
[0222] 2. Prepare a control sample with no carbonation and
admixture for desired "control" workability, if admixture is used.
[0223] 3. CO.sub.2 uptake dosage ramp: Prepare one or more
carbonated samples with incrementally higher CO.sub.2 dosages. A
chemical admixture may be included to restore workability, and/or
to enhance early strength development. Admixtures themselves may be
optimized by preparing carbonated samples with fixed CO2 dose and
variable admixture type and dosing (e.g. compare gluconate vs
fructose, before and after CO.sub.2, with dispersant) [0224] 4.
Plot the power/heat flow rate for each mix as a function of time
[0225] 5. Plot the integrated power/heat flow rate, energy/heat of
hydration, as a function of time, excluding the initial exotherm
occurring prior to the onset of the main hydration peak in the heat
flow plot. See ASTM C 1679 for the definition of the main hydration
peak. [0226] The following features from the heat flow rate plot
and the heat of hydration are indicative of accelerated development
of set or early strength: [0227] a) If the onset of the main
hydration peak in the power/heat flow rate plot occurs sooner for a
carbonated mix then this indicates accelerated set and early
strength development [0228] b) If the energy/heat of hydration for
a carbonated mix exceeds the heat of hydration for the control mix
then this indicates a continuously higher early strength during the
time that the heat of hydration stays above the control. [0229] c)
If the results from several different CO.sub.2 dosages and/or
admixture dosages are obtained then one can use the results not
only to identify cements that responds favorably to carbonation,
but also to "dial-in" the optimum CO.sub.2 uptake and admixture
dose for said cement with respect to the development of mechanical
properties at early age.
[0230] The information obtained is especially useful for evaluating
cements suitable for carbonation in pre-cast applications and any
other application where accelerated set and early strength is of
value. Optionally, samples can be prepared for testing of strength
development, to verify the calorimetry results. In general,
admixtures are used to restore workability in order to generate
well compacted samples with reliable strength data. Doses for
carbon dioxide and, optionally, types and doses of admixture, for a
given mix may thus be determined rapidly and efficiently, then the
dose determined in the testing is used in the actual
carbonation.
[0231] In low dose carbonation, as in all cement mix, e.g.,
concrete, carbonation, various factors may be manipulated to
produce optimal or desired results. These include one or more of:
time after beginning of mixing at which carbon dioxide is applied;
number of doses of carbon dioxide; rate at which carbon dioxide is
supplied to the mixing chamber; form of the carbon dioxide (gas,
solid, and/or dissolved in water); and the like. Mixing is said to
have commenced upon addition of the first aliquot of water to the
cement-containing mix. It will be appreciated that in certain
instances, components of a concrete mix, e.g., aggregate, may be
wet and that "the first mix water" may be the water on the
aggregate. Carbon dioxide can be supplied to a mix before the first
addition of water, for example by flooding a chamber or head space
with carbon dioxide before water addition, but in this case the
application of carbon dioxide is considered to occur when the first
water is added, since virtually no reaction will occur until the
carbon dioxide dissolves in the mix water.
[0232] In certain operations, e.g., precast operations, there is
little flexibility as to when carbon dioxide is added to the mixing
concrete, as mix times are generally very short and the concrete is
typically used very quickly after mixing. In these operations,
addition of carbon dioxide to the mixing concrete generally begins
simultaneously with the commencement of mixing or within seconds
or, at most, minutes of the commencement of mixing. In other
operations, e.g., ready-mix operations, there are several times at
which carbon dioxide can be added to the mixing concrete. Carbon
dioxide can be added during batching, which can occur either in a
fixed mixer or in the drum of the ready-mix truck; in this case,
the carbon dioxide contacts the hydrating cement at a time very
close to the commencing of mixing, as in the precast case. Some
ready-mix operations include one or more additional operations
after batching but before the truck has left the batching facility,
e.g., a wash station for washing the truck after batching, and in
these operations carbon dioxide may be alternatively or
additionally added at the batching facility after batching, e.g.,
at a wash station, which will involve carbon dioxide addition at a
time several minutes after mixing commences. Additionally or
alternatively, carbon dioxide may be added at the job site after
the concrete has been transported, and in these cases carbon
dioxide addition will be added to mixing concrete at a time up to
several hours after mixing commences. Any suitable combination of
these approaches may be used.
[0233] Thus, in certain embodiments, carbon dioxide is applied to
the mix at 0 minutes, that is, carbon dioxide is present to the mix
chamber when the first mix water is supplied, or supplying carbon
dioxide to the mix chamber commences when the first mix water is
applied, or both. In certain embodiments, carbon dioxide is applied
at least 0, 1, 5, 10, 20, 30, 40, or 50 seconds, or 1, 2, 5, 10,
15, 20, 30, 40, 50, 60, 70, 80, or 90 minutes after mixing
commences, and/or not more than 1, 2, 5, 10, 15, 20, 30, 40, 50,
60, 70, 80, 90, 120, 180, 240, or 300 minutes after mixing
commences. The duration of carbon dioxide delivery can be less than
or equal to 10, 8, 7, 6, 5, 4, 3, 2, or 1 minute, or less than or
equal to 50, 40, or 30 seconds, and/or more than or equal to 5, 10,
20, 30, 40, or 50 seconds, or more than or equal to 1, 2, 3, 4, 5,
6, 7, or 8 minutes. In certain embodiments, the duration of carbon
dioxide delivery is 5 seconds to 5 minutes. In certain embodiments,
the duration of carbon dioxide delivery is 10 seconds to 4 minutes.
In certain embodiments, the duration of carbon dioxide delivery is
20 seconds to 3 minutes. In certain embodiments, carbon dioxide
delivery commences not more than 1 minute after mixing commences.
For example, in the case of carbon dioxide supplied to a concrete
mix in a ready mix truck, the mix components, including at least
part of the mix water, may be added to the truck, and it may be
desirable that carbon dioxide addition not commence until at least
2, 3 or 4 minutes or more after mixing has commenced. Such addition
could occur, e.g., at a wash station, where the driver stops to
wash the truck before commencing delivery; the truck is usually
stopped at the wash station for at least 5-10 minutes, and an
on-site carbon dioxide delivery system can be used to supply carbon
dioxide to the drum of the truck during the wash station stop. Part
or all of the dose of carbon dioxide can be delivered in this
manner, for example by delivering carbon dioxide to the truck
through the water line (though any suitable route may be used); in
embodiments where a carbon dioxide source is attached to the truck
there may be some mechanism to remind the driver to detach it
before departing, such as an alarm. Alternatively, or additionally,
the desirable time for addition of carbon dioxide to the mix may be
later in the mix time, such as at a time that the truck is normally
en route to the job site, or at the job site. In this case, a
portable source of carbon dioxide may be attached to the truck,
with suitable valving and tubing, so as to deliver one or more
doses of carbon dioxide to the drum of the truck at a later time,
such as at least 15, 30, or 60 minutes after mixing commences. A
controller, which may be self-contained or may be remotely
activated and which may send signals to a remote site regarding
dosing and other information, may be included in the system so that
dosing commences at a predetermined time after mixing commences and
continues for a predetermined time, or continues until some
predetermined characteristic or characteristics of the concrete mix
is detected. Alternatively, the time and/or duration of dosing may
be manually controlled, or subject to manual override. The carbon
dioxide source can be as simple as a pressurized tank of gaseous
carbon dioxide, which can be topped off periodically, for example
when the truck returns to the batching site, to ensure a sufficient
supply of carbon dioxide for any ensuing round of carbonation,
e.g., without the need to ascertain carbon dioxide levels in the
tank. In these embodiments, some or all of the carbonation may
occur at the job site, for example, based on determination of one
or more characteristics of the concrete.
[0234] The rate of delivery of the carbon dioxide may be any
desired rate and the rate may be controlled. A slower rate of
delivery may be desired, especially in wet mix operations such as
ready mix operations, where the higher w/c ratio is known to slow
carbonation compared to lower w/c operations, e.g., some precast
operations. One example for controlling the rate of delivery is to
divide the total dose of carbon dioxide into two or more smaller
doses. Thus, the carbon dioxide may be delivered as a single dose,
or as multiple doses, for example, as at least 2, 3, 4, 5, 6, 7, 8,
9, or 10 doses, and/or not more than 3, 4, 5, 6, 7, 8, 9, 10, 12,
15, or 20 doses; such as 2-10 doses, or 2-5 doses. Each dose may be
equal in size to the others or different, and the interval between
doses may be timed equally or not, as desired. The exact number and
size of the doses may be predetermined, or it may be dictated by
one or more characteristics of the mix that are monitored. The
carbon dioxide may be in any suitable form, such as gas, or a
gas/solid mix.
[0235] In addition or alternatively, for slower rates of delivery
where the rate is controlled, gaseous carbon dioxide carbon dioxide
may be delivered at a controlled, relatively slow rate. Thus, in
some embodiments, the carbon dioxide is delivered at least in part
as a gas at a controlled rate, where the rate may be not more than
5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 150, 200, 300,
400, 500, 600, 700, or 800 SLPM (standard liters per minute), and
or not less than 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 150,
200, 300, 400, 500, 600, 700, 800, or 900 SLPM. For example, in a
ready mix truck en route to a job site, the carbon dioxide may be
delivered at a rate such that the full dose is delivered while the
truck is in transit, e.g., by a portable dosing system as described
above, over a period of many minutes or even an hour or more, such
as at a rate of 100 to 600 SLPM, or even lower rates. The rate of
delivery may be constant, or it may be varied according to a
predetermined schedule, or as dictated by one or more
characteristics of the concrete mix that are monitored. Either or
both of divided doses and controlled rate dosing may be used, as
desired or dictated by the particular mix and job requirements.
[0236] The methods and compositions of the invention allow for very
high levels of efficiency of uptake of carbon dioxide into the
mixing concrete, where the efficiency of uptake is the ratio of
carbon dioxide that remains in the mixing concrete as stable
reaction products to the total amount of carbon dioxide to which
the mixing concrete is exposed. In certain embodiments, the
efficiency of carbon dioxide uptake is at least 40, 50, 60, 70, 80,
90, 95, 96, 97, 98, 99, or 99%, or 40-100, 50-100, 60-100, 70-100,
80-100, 90-100, 40-99, 50-99, 60-99, 70-99, 80-99, or 90-99%.
[0237] In a wet cast operation, the addition of carbon dioxide,
components of the cement mix, e.g., hydraulic cement mix, such as
one or more admixtures, described more fully below, may be adjusted
so that flowability of the final cement mix, e.g., hydraulic cement
mix is within 10% of the flowability that would be achieved without
the addition of carbon dioxide. In certain embodiments, the
addition of carbon dioxide, components of the cement mix, e.g.,
hydraulic cement mix, such as one or more admixtures, described
more fully below, are adjusted so that flowability of the final
cement mix, e.g., hydraulic cement mix is within 50, 40, 30, 20 15,
10, 8, 5, 4, 3, 2, or 1% of the flowability that would be achieved
without the addition of carbon dioxide, or of a predetermined
flowability. In certain embodiments, the addition of carbon
dioxide, components of the cement mix, e.g., hydraulic cement mix,
such as one or more admixtures, described more fully below, are
adjusted so that flowability of the final cement mix, e.g.,
hydraulic cement mix is within 20% of the flowability that would be
achieved without the addition of carbon dioxide, or a predetermined
flowability. In certain embodiments, the addition of carbon
dioxide, components of the cement mix, e.g., hydraulic cement mix,
such as one or more admixtures, described more fully below, are
adjusted so that flowability of the final cement mix, e.g.,
hydraulic cement mix is within 10% of the flowability that would be
achieved without the addition of carbon dioxide, or a predetermined
flowability. In certain embodiments, the addition of carbon
dioxide, components of the cement mix, e.g., hydraulic cement mix,
such as one or more admixtures, described more fully below, are
adjusted so that flowability of the final cement mix, e.g.,
hydraulic cement mix is within 5% of the flowability that would be
achieved without the addition of carbon dioxide, or a predetermined
flowability. In certain embodiments, the addition of carbon
dioxide, components of the cement mix, e.g., hydraulic cement mix,
such as one or more admixtures, described more fully below, are
adjusted so that flowability of the final cement mix, e.g.,
hydraulic cement mix is within 2% of the flowability that would be
achieved without the addition of carbon dioxide, or a predetermined
flowability. In certain embodiments, the addition of carbon
dioxide, components of the cement mix, e.g., hydraulic cement mix,
such as one or more admixtures, described more fully below, are
adjusted so that flowability of the final cement mix, e.g.,
hydraulic cement mix is within 1-50%, or 1-20%, or 1-10%, or 1-5%,
or 2-50%, or 2-20%, or 2-10%, or 2-5% of the flowability that would
be achieved without the addition of carbon dioxide, or a
predetermined flowability.
A. Admixtures
[0238] Admixtures are often used in cement mix, e.g., hydraulic
cement mixes, such as concrete mixes, to impart desired properties
to the mix. Admixtures are compositions added to a cement mix,
e.g., hydraulic cement mix such as concrete to provide it with
desirable characteristics that are not obtainable with basic cement
mix, e.g., hydraulic cement mixes, such as concrete mixtures or to
modify properties of the cement mix, e.g., hydraulic cement mix,
i.e., concrete to make it more readily useable or more suitable for
a particular purpose or for cost reduction. An admixture is any
material or composition, other than the hydraulic cement, aggregate
and water, that is used as a component of the cement mix, e.g.,
hydraulic cement mix, such as concrete or mortar to enhance some
characteristic, or lower the cost, thereof. In some instances, the
desired cement mix, e.g., hydraulic cement mix, e.g., concrete
performance characteristics can only be achieved by the use of an
admixture. In some cases, using an admixture allows for the use of
less expensive construction methods or designs, the savings from
which can more than offset the cost of the admixture.
[0239] In certain embodiments, the carbonated cement mix, e.g.,
hydraulic cement mixture, e.g., concrete, may exhibit enhanced
characteristics when compared with the same mixture that was not
exposed to carbon dioxide. This can depend on the type of cement
used in the carbonated cement mix and/or the dose of carbon dioxide
used and final carbonation achieved. In this sense, carbon dioxide
can itself act as an admixture. For example, in certain
embodiments, the carbonated cement mix, e.g., concrete mixture, has
superior properties such as greater strength, such as greater 1-,
7-, or 28-day strength, e.g., at least 1, 2, 3, 4, 5, 7, 10, 15,
20, 30, or 40% greater strength than the non-carbonated concrete
mixture at 1-, 7-, or 28-days. In general herein, "strength" refers
to compressive strength, as that term is generally understood in
the art. In certain embodiments, the carbonated cement mix, e.g.
concrete, may exhibit accelerated set compared to non-carbonated
mix, such as a faster time to initial set (for example,
penetrometer measurement of 500 psi according to ASTM C403) or a
faster time to final set (for example, penetrometer measurement of
4000 psi according to ASTM C403), or both, such as less than 95,
90, 85, 80, 75, 70, 65, 60, 55, 50, 40, 30, or 20% of the initial
or final set time compared to uncarbonated mix. Carbonated cement
mix, e.g., hydraulic cement mixes may also provide final concrete
mixtures that have lower water absorption as compared to
non-carbonated, such as at least 1, 2, 3, 4, 5, 7, 10, 15, 20, 30,
or 40% lower water absorption. The carbonated cement mix, e.g.,
hydraulic cement mix, i.e., concrete, may also produce a final
product that is lower in density but of comparable strength
compared to non-carbonated, such as at least 1, 2, 3, 4, 5, 7, 10,
15, 20, 30, or 40% lower density with a compressive strength within
1, 2, 3, 4, 5, 7, 10, 15, or 20% of the non-carbonated, e.g., at
least 5% lower density with a compressive strength within 2%.
[0240] However, depending on the mix design, the carbonated cement
mix, e.g., hydraulic cement mixture, i.e., concrete, may
alternatively or in addition, exhibit properties that it is desired
to modulate, such as by the addition of an admixture. For example,
carbonated cement mix, e.g., hydraulic cement mix for use in a wet
cast operation may have workability/flow characteristics that are
not optimum for a wet cast operation without addition of an
admixture or other manipulation of the mix, e.g., addition of extra
water. As another example, carbonated mixes may have strength
characteristics, e.g., compressive strength at one or more time
points, that are not optimum without addition of an admixture or
other manipulation of the mix. In some cases, the mix design will
already call for an admixture, whose effect on the properties of
the mix may be affected by the carbonation, requiring coordination
of the timing of the admixture in relation to the carbon dioxide
addition, or other manipulation. In addition, an admixture may be
used to modulate one or more aspects of the carbonation itself, for
example, to increase the rate of uptake of the carbon dioxide.
[0241] Concrete may be used in wet cast operations, such as in
certain precast operations or in ready mix trucks that transport
the concrete to a job site where it is used, e.g., poured into
molds or otherwise used at the site, or in dry cast operations,
which are precast operations. In the case of a wet cast operation,
the flowability of the concrete should be maintained at a level
compatible with its use in the operation, e.g., in the case of a
ready mix truck, at the job site; whereas for a dry cast operation
concrete that does not flow (zero slump) is desirable. In both dry
cast and wet cast operations, strength, e.g., compressive strength,
is important, both in the short term so that the concrete can be
allowed to stand alone, e.g., molds can be removed, cast objects
can be manipulated, etc., in the shortest possible time, and also
in the long term so that a required final strength is reached.
Flowability of a mix may be evaluated by measuring slump; strength
may be evaluated by one or more strength tests, such as compressive
strength. Other properties that may be affected by carbonation; in
some cases the effect is a positive one, but if the effect is a
negative one, corrected through the use of one or more admixtures.
Such properties include shrinkage and water absorption.
[0242] In certain cases carbonation of the cement mix, e.g.,
hydraulic cement mix may affect flowability of a cement mix, e.g.,
hydraulic cement mix, i.e., a concrete mix, to be used in a wet
cast operation, such as in a ready mix truck transporting the mix
to a job site. Thus in certain embodiments in which a carbonated
mix is produced (such as for use with a readymix truck), one or
more admixtures may be added to modulate the flowability of the
carbonated mixture, either before, during, or after carbonation, or
any combination thereof, such that it is within a certain
percentage of the flowability of the same mixture without
carbonation, or of a certain predetermined flowability. The
addition of carbon dioxide, components of the mix, e.g., concrete
mix, and/or additional components such as one or more admixtures,
may be adjusted so that flowability of the final mix is within 50,
40, 30, 20, 10, 8, 5, 4, 3, 2, 1, 0.5, or 0.1% of the flowability
that would be achieved without the addition of carbon dioxide, or
of a certain predetermined flowability. In certain embodiments, the
addition of carbon dioxide, components of the mix, and/or
additional components such as one or more admixtures, may be
adjusted so that flowability of the final mix is within 20% of the
flowability that would be achieved without the addition of carbon
dioxide, or within 20% of a predetermined desired flowability. In
certain embodiments, the addition of carbon dioxide, components of
the mix, and/or additional components such as one or more
admixtures, may be adjusted so that flowability of the final mix is
within 10% of the flowability that would be achieved without the
addition of carbon dioxide, or within 10% of a predetermined
desired flowability. In certain embodiments, the addition of carbon
dioxide, components of the mix, and/or additional components such
as one or more admixtures, may be adjusted so that flowability of
the final mix is within 5% of the flowability that would be
achieved without the addition of carbon dioxide, or within 5% of a
predetermined desired flowability. In certain embodiments, the
addition of carbon dioxide, components of the mix, and/or
additional components such as one or more admixtures, may be
adjusted so that flowability of the final mix is within 2% of the
flowability that would be achieved without the addition of carbon
dioxide, or within 2% of a predetermined desired flowability. Any
suitable measurement method for determining flowability may be
used, such as the well-known slump test. Any suitable admixture may
be used, as described herein, such as carbohydrates or carbohydrate
derivatives, e.g., fructose, sucrose, glucose, sodium
glucoheptonate, or sodium gluconate, such as sodium glucoheptonate
or sodium gluconate.
[0243] In certain embodiments, one or more admixtures may be added
to modulate the mix so that a desired strength, either early
strength, late strength, or both, may be achieved. Strength of the
carbonated cement mix can be dependent on mix design, thus,
although with some mix designs carbonation may increase strength at
one or more time points, in other mix designs carbonation may
decrease strength at one or more time points. See Examples for
various mix designs in which carbonation increased or decreased
strength at one or more time points. In some cases, carbonation
decreases strength at one or more time points and it is desired to
return the strength at the time point to within a certain
acceptable limit. In certain cases, one or more admixtures is added
to increase strength beyond that seen in non-carbonated concrete of
the same density. This may be done, e.g., to produce a lightweight
concrete with strength comparable to the denser, non-carbonated
concrete. In other cases, one or more admixtures added to a
carbonated cement itself causes or exacerbates strength loss, and
it is desired to recover the loss. Thus, in certain embodiments an
admixture is added to the carbonated mix, either before, during, or
after carbonation, or a combination thereof, under conditions such
that the carbonated mix exhibits strength, e.g., 1-, 7-, 28 and/or
56-day compressive strength, within a desired percentage of the
strength of the same mix without carbonation, or of a predetermined
strength, e.g., within 50, 40, 30, 20, 15, 12, 10, 9, 8, 7, 6, 5,
4, 3, 2, 1, 0.5, or 0.1%. In certain embodiments, the addition of
carbon dioxide, components of the mix, and/or additional components
such as one or more admixtures, may be adjusted so that strength at
a given time point of the final mix is within 20% of the strength
that would be achieved without the addition of carbon dioxide, or
within 20% of a predetermined desired strength. In certain
embodiments, the addition of carbon dioxide, components of the mix,
and/or additional components such as one or more admixtures, may be
adjusted so that strength at a given time point of the final mix is
within 10% of the strength that would be achieved without the
addition of carbon dioxide, or within 10% of a predetermined
desired strength. In certain embodiments, the addition of carbon
dioxide, components of the mix, and/or additional components such
as one or more admixtures, may be adjusted so that strength at a
given time point of the final mix is within 5% of the strength that
would be achieved without the addition of carbon dioxide, or within
5% of a predetermined desired strength. In certain embodiments, the
addition of carbon dioxide, components of the mix, and/or
additional components such as one or more admixtures, may be
adjusted so that strength at a given time point of the final mix is
within 2% of the strength that would be achieved without the
addition of carbon dioxide, or within 2% of a predetermined desired
strength. In certain embodiments the strength is a compressive
strength. Any suitable method to test strength, such as flexural or
compressive strength, may be used so long as the same test is used
for samples with and without carbonation. Any suitable admixtures
to achieve the desired strengths may be used, such as the
admixtures described herein.
[0244] Other properties, such as water absorption, shrinkage,
chloride permeability, and the like, may also be tested and
adjusted in a similar manner, and to similar percentages, as for
flowability and/or shrinkage.
[0245] It will be appreciated that more than one admixture may be
used, for example, 2, 3, 4, 5, or more than 5 admixtures. For
example, certain admixtures have desirable effects on flowability
but undesirable effects on strength development; when such an
admixture is used, a second admixture that accelerates strength
development may also be used.
[0246] Any suitable admixture that has the desired effect on the
property or properties of the carbonated cement that it is desired
to modified may be used. TABLE 1 lists exemplary classes and
examples of admixtures that can be used, e.g., to modulate the
effects of carbonation.
TABLE-US-00001 TABLE 1 Admixtures for use with carbonated cement
Cement Chemical Class Sub Class Application Examples Saccharides
Sugars Retarder Fructose, glucose, sucrose Sugar Acids/bases
Retarder Sodium Gluconate, sodium glucoheptonate Organic Polymers
Polycarboxylic Plasticizer Many commercial brands Ethers Sulfonated
Plasticizer Many commercial brands Napthalene Formaldehyde
Sulphonated Plasticizer Many commercial brands Melamine
formaldehyde Ligno sulphonates Plasticizer Many commercial brands
Inorganic Salts Alkaline Earth Accelerant Ca(NO.sub.3).sub.2,
Mg(OH).sub.2 Metal Containing Alkali Metal Accelerant NaCl, KOH
Containing Carbonate -- NaHCO.sub.3, Na.sub.2CO.sub.3 containing
Alkanolamines Tertiary Accelerants/Grinding Triethanolamine,
alkanolamines aids Triisopropylamine Phosphonates -- Retarders
Nitrilotri(methylphosphonic acid), 2-phosphonobutane-
1,2,4-tricarboxylic acid Surfactants Vinsol Resins, Air Entraining
Many commercial brands synthetic Agents surfactants Chelating
Agents Various Retarders EDTA, Citric Acid, Chemistries
nitrilotriacetic acid
[0247] In certain embodiments, one or admixtures is added to a
cement mix, e.g., hydraulic cement mix, before, during, or after
carbonation of the mix, or a combination thereof, where the
admixture is a set retarder, plasticizer, accelerant, or air
entraining agent. Where it is desired to modulate flowability, set
retarders and plasticizers are useful. Where it is desired to
modulate strength development, accelerants are useful. If it is
desired to increase the rate of carbon dioxide uptake, certain air
entraining agents may be useful.
[0248] Set retarders include carbohydrates, i.e., saccharides, such
as sugars, e.g., fructose, glucose, and sucrose, and sugar
acids/bases and their salts, such as sodium gluconate and sodium
glucoheptonate; phosphonates, such as nitrilotri(methylphosphonic
acid), 2-phosphonobutane-1,2,4-tricarboxylic acid; and chelating
agents, such as EDTA, Citric Acid, and nitrilotriacetic acid. Other
saccharides and saccharide-containing admixes include molasses and
corn syrup. In certain embodiments, the admixture is sodium
gluconate. Other exemplary admixtures that can be of use as set
retarders include sodium sulfate, citric acid, BASF Pozzolith XR,
firmed silica, colloidal silica, hydroxyethyl cellulose,
hydroxypropyl cellulose, fly ash (as defined in ASTM C618), mineral
oils (such as light naphthenic), hectorite clay, polyoxyalkylenes,
natural gums, or mixtures thereof, polycarboxylate
superplasticizers, naphthalene HRWR (high range water reducer).
Additional set retarders that can be used include, but are not
limited to an oxy-boron compound, lignin, a polyphosphonic acid, a
carboxylic acid, a hydroxycarboxylic acid, polycarboxylic acid,
hydroxylated carboxylic acid, such as fumaric, itaconic, malonic,
borax, gluconic, and tartaric acid, lignosulfonates, ascorbic acid,
isoascorbic acid, sulphonic acid-acrylic acid copolymer, and their
corresponding salts, polyhydroxysilane, polyacrylamide.
Illustrative examples of retarders are set forth in U.S. Pat. Nos.
5,427,617 and 5,203,919, incorporated herein by reference.
[0249] Accelerants include calcium-containing compounds, such as
CaO, Ca(NO.sub.2).sub.2, Ca(OH).sub.2, calcium stearate, or
CaCl.sub.2, and magnesium-containing compounds, such as magnesium
hydroxide, magnesium oxide, magnesium chloride, or magnesium
nitrate. Without being bound by theory, it is thought that, in the
case of carbonated cement, the added calcium or magnesium compound
may provide free calcium or magnesium to react with the carbon
dioxide, providing a sink for the carbon dioxide that spares the
calcium in the cement mix, or providing a different site of
carbonation than that of the cement calcium, or both, thus
preserving early strength development. In certain embodiments, CaO
(lime) may be added to the mix, or a high-free lime cement may be
the preferred cement for the mix. For example, in certain
embodiments, the free lime (CaO) content of the cement used in a
particular cement mixture, such as mortar or concrete, may be
increased by the addition of CaO to the mixture, generally before
the mixture is exposed to carbon dioxide, such as by addition of
0.01-50%, or 0.01-10%, or 0.01-5%, or 0.01-3%, or 0.01-2%, or
0.01-1% CaO, or 0.1-50%, or 0.1-10%, or 0.1-5%, or 0.1-3%, or
0.1-2%, or 0.1-1%, or 0.2-50%, or 0.2-10%, or 0.2-5%, or 0.2-3%, or
0.2-2% CaO, or 0.2-1%, or 0.5-50%, or 0.5-10%, or 0.5-5%, or
0.5-3%, or 0.5-2% CaO, or 0.5-1% CaO bwc. Alternatively, CaO may be
added so that the overall CaO content of the cement mixture reaches
a desired level, such as 0.5-10%, or 0.5-5%, or 0.5-3%, or 0.5-2%,
or 0.5-1.5%, or at least 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2,
1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.2, 2.5, 3.0, 4.0, 5.0,
6.0, 7.0, 8.0, 9.0, 10%, 20%, 30%, 40%, or 50% CaO bwc. The added
CaO will generally also increase the rate of uptake of carbon
dioxide by the mix during mixing, thus allowing a greater carbon
dioxide uptake for a given time of exposure, or a lower time of
exposure to achieve a given level of uptake. Other set accelerators
include, but are not limited to, a nitrate salt of an alkali metal,
alkaline earth metal, or aluminum; a nitrite salt of an alkali
metal, alkaline earth metal, or aluminum; a thiocyanate of an
alkali metal, alkaline earth metal or aluminum; an alkanolamine; a
thiosulfate of an alkali metal, alkaline earth metal, or aluminum;
a hydroxide of an alkali metal, alkaline earth metal, or aluminum;
a carboxylic acid salt of an alkali metal, alkaline earth metal, or
aluminum (preferably calcium formate); a polyhydroxylalkylamine; a
halide salt of an alkali metal or alkaline earth metal (e.g.,
chloride).
[0250] The admixture or admixtures may be added to any suitable
final percentage (bwc), such as in the range of 0.01-0.5%, or
0.01-0.3%, or 0.01-0.2%, or 0.01-0.1%, or 0.01-1.0%, or 0.01-0.05%,
or 0.05% to 5%, or 0.05% to 1%, or 0.05% to 0.5%, or 0.1% to 1%, or
0.1% to 0.8%, or 0.1% to 0.7% per weight of cement. The admixture
may be added to a final percentage of greater than 0.01, 0.02,
0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.3, 0.4,
or 0.5%; in certain cases also less than 5, 4, 3, 2, 1, 0.9, 0.8,
0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05,
0.04, 0.03, or 0.02%.
[0251] It has been observed that the timing of addition of a given
admixture relative to carbonation of a cement mix, e.g., hydraulic
cement mix may alter the effects of the admixture on the properties
of the cement mix, e.g., hydraulic cement mix, e.g., effects on
flowability or strength. For example, in certain mix designs, the
addition of sodium gluconate after carbonation restores flowability
to desired levels, but may adversely affect early strength
development; whereas the addition of sodium gluconate before
carbonation maintains early strength development but does not
optimally restore flowability. As another example, in mix designs
in which an air entrainer is desired, it has been found that if the
air entrainer is added before carbonation, the density of the mix
is increased compared to if the air entrainer is added after
carbonation. The admixture or admixtures thus may be added before,
during, or after carbonation of the cement mix, e.g., hydraulic
cement mix, or any combination thereof. For example, in certain
embodiments, the admixture is added after carbonation; in other
embodiments, the admixture is added before carbonation; in yet
other embodiments, the admixture is added in two split doses, one
before carbonation and one during and/or after carbonation. It will
be apparent that if more than one admixture is used, one may be
added at one time while another is added at another time, for
example, in a mix where an air entrainer is used and sodium
gluconate is also added to affect flowability, the sodium gluconate
may be added in split doses, one before carbonation and one
during/after carbonation, and the air entrainer may be added after
carbonation. The latter is exemplary only, and any suitable
combination of admixtures and timing to achieve the desired effect
or effects may be used.
[0252] It has been observed that the effects of carbonation and of
admixtures on carbonated cement mix, e.g., hydraulic cement mixes
is highly mix-specific. In some cases carbonation actually improves
the properties of a mix, especially in dry cast situations where
flowability is not an issue, and no admixture is required. In other
cases, especially in wet cast situations where flowability is an
issue, one or more admixtures may be required to restore one or
more properties of the mix. Whether or not admixture is added,
and/or how much is added, to a given batch may be determined by
pre-testing the mix to determine the properties of the carbonated
mix and the effects of a given admixture. In some cases the
admixture and/or amount may be predicted based on previous tests,
or on properties of the cement used in the mix, or on theoretical
considerations. It has been found that different cements have
different properties upon carbonation, and also react differently
to a given admixture, and the invention includes the use of a
library of data on various cement types and admixtures so as to
predict a desired admixture/amount for a mix design, which may be a
mix that is the same as or similar to a mix in the library, or a
new mix whose properties can be predicted from the library. In
addition, for a given batch, rheology (flowability) may be
monitored during the carbonation of the batch and the exact timing
and/or amount of admixture added to that particular batch, or to
subsequent batches, may be adjusted based on the feedback obtained.
A combination of predicted value for admixture type, timing, and/or
amount, and modification of the value based on real-time
measurements in a given batch or batches may be used.
[0253] In certain embodiments, an admixture comprising a
carbohydrate or carbohydrate derivative is added to a cement mix,
e.g., hydraulic cement mix before, during, and/or after carbonation
of the mix, or a combination thereof. In certain embodiments, the
admixture is added after carbonation of the cement mix, e.g.,
hydraulic cement mix, or during and after carbonation. The
carbonation may be accomplished as described herein, for example,
by delivering carbon dioxide to the surface of the cement mix,
e.g., hydraulic cement mix during mixing. The carbohydrate or
derivative may be any carbohydrate as described herein, for example
sucrose, fructose, sodium glucoheptonate, or sodium gluconate. In
certain embodiments, the carbohydrate is sodium gluconate. The
carbohydrate or derivative, e.g., sodium gluconate may be used at a
suitable concentration; in some cases, the concentration is greater
than 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.05%,
0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.15%, 0.2%, 0.3%, 0.4%, or 0.5%
bwc. The concentration may also be less than 2, 1.5, 1, 0.9, 0.8,
0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1%. For example, in certain
embodiments, sodium gluconate is used as an admixture at a dose of
between 0.01 and 1% bwc, or between 0.01 and 0.8%, or between 0.01
and 0.5%, or between 0.01 and 0.4% bwc, or between 0.01 and 0.3%,
or between 0.01 and 0.2% bwc, or between 0.01 and 0.1%, or between
0.01 and 0.05%, or between 0.03 and 1% bwc, or between 0.03 and
0.8%, or between 0.03 and 0.5%, or between 0.03 and 0.4% bwc, or
between 0.03 and 0.3%, or between 0.03 and 0.2% bwc, or between
0.03 and 0.1%, or between 0.03 and 0.08%, or between 0.05 and 1%
bwc, or between 0.05 and 0.8%, or between 0.05 and 0.5%, or between
0.05 and 0.4% bwc, or between 0.05 and 0.3%, or between 0.05 and
0.2% bwc, or between 0.05 and 0.1%, or between 0.05 and 0.08%, or
between 0.1 and 1% bwc, or between 0.1 and 0.8%, or between 0.1 and
0.5%, or between 0.1 and 0.4% bwc, or between 0.1 and 0.3%, or
between 0.1 and 0.2% bwc. The sodium gluconate may be added before,
during, or after carbonation of the mix, or any combination
thereof, and may be added as one, two, three, four, or more than
four divided doses. The carbohydrate or derivative may be added in
two or more doses, such as one dose before carbonation and one dose
during and/or after carbonation. In certain embodiments, calcium
stearate is used as an admixture.
[0254] In certain embodiments, a second admixture is also used,
such as any of the admixtures described herein. In certain
embodiments, the second admixture is a strength accelerator. In
certain embodiments, a third admixture is also used, such as any of
the admixtures described herein. In certain embodiments, a fourth
admixture is also used, such as any of the admixtures described
herein.
[0255] In certain embodiments, an admixture is used that modulates
the formation of calcium carbonate so that one or more polymorphic
forms is favored compared to the mixture without the admixture,
e.g., modulates the formation of amorphous calcium carbonate, e.g.,
aragonite, or calcite. Exemplary admixtures of this type include
organic polymers such as polyacrylate and polycarboxylate ether,
phosphate esters such as hydroxyamino phosphate ester, phosphonate
and phosphonic acids such as nitrilotri(methylphosphonic acid),
2-phosphonobutane-1,2,4-tricarboxylic acid, chelators, such as
sodium gluconate, ethylenediaminetetraacetic acid (EDTA), and
citric acid, or surfactants, such as calcium stearate.
[0256] Other admixtures useful in methods and compositions of the
invention are described in U.S. Pat. No. 7,735,274, hereby
incorporated by reference herein in its entirety.
B. Supplementary Cementitious Materials and Cement Replacements
[0257] In certain embodiments, one or more supplementary
cementitious materials (SCMs) and/or cement replacements are added
to the mix at the appropriate stage for the particular SCM or
cement replacement. In certain embodiments, an SCM is used. Any
suitable SCM or cement replacement may be used; exemplary SCMs
include blast furnace slag, fly ash, silica fume, natural pozzolans
(such as metakaolin, calcined shale, calcined clay, volcanic glass,
zeolitic trass or tuffs, rice husk ash, diatomaceous earth, and
calcined shale), and waste glass. Further cement replacements
include interground limestone, recycled/waste plastic, scrap tires,
municipal solid waste ash, wood ash, cement kiln dust, foundry
sand, and the like. In certain embodiments, an SCM and/or cement
replacement is added to the mix in an amount to provide 0.1-50%, or
1-50%, or 5-50%, or 10-50%, or 20-50%, or 1-40%, or 5-40%, or
10-50%, or 20-40% bwc. In certain embodiments, an SCM is used and
the SCM is fly ash, slag, silica fume, or a natural pozzolan. In
certain embodiment, the SCM is fly ash. In certain embodiments, the
SCM is slag.
[0258] It is well-known that addition of an SCM such as fly ash or
slag to a cement mix, e.g., concrete mix, can retard early strength
development; indeed, when weather becomes cold enough, the use of
SCM in mixes is curtailed because the early strength development is
sufficiently retarded as to make the use of the mix problematic. In
addition, the maximum amount of SCM that may be added to a mix can
be limited by its effect on early strength development. The present
inventors have found that even very low doses of carbon dioxide,
when added to a concrete mix containing SCM, can accelerate early
strength development and thus could allow such mixes to be used
under circumstances where they otherwise might not be used, e.g.,
in cold weather, or in greater amounts, thus extending the
usefulness of such mixes, such as extending the useful season for
such mixes, or increasing the proportion of SCM in a given mix, or
both.
[0259] In certain embodiments the invention provides methods and
compositions for the expanding the range of conditions under which
an SCM may be used in a concrete mix by carbonating the mix. The
range of conditions may include the temperature at which the
SCM-containing mix may be used, or the amount of SCM that may be
added while maintaining adequate early strength development, or the
early strength for a given amount of SCM in a mix.
[0260] In certain embodiments, the invention provides a method for
decreasing the minimum temperature at which an SCM-concrete mix may
be used, thus increasing the overall acceptable temperature range
for the SCM-concrete mix, by exposing the SCM-concrete mix to a
dose of carbon dioxide sufficient to modulate, e.g., accelerate,
early strength development and/or set of the mix to a level at
which the mix may be used at a temperature below that at which it
could have been used without the carbon dioxide exposure. The dose
can be such that the early strength development of the mix allows
its use in a desired manner at a temperature that is at least 1, 2,
3, 4, 5, 6, 8, 9, or 10.degree. C. below the temperature at which
it could be used without the carbon dioxide treatment and/or not
more than 2, 3, 4, 5, 6, 8, 9, 10, or 12.degree. C. below the
temperature at which it could be used without the carbon dioxide
treatment. The dose of carbon dioxide added to the mix to achieve
the desired increase in early strength development can be not more
than 2.0, 1.5, 1.2, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2,
0.1, or 0.05% carbon dioxide bwc. The dose can be such that the
early strength development of the mix, e.g., the strength at 8, 12,
16, 20, or 24 hours, or any other suitable time point for early
strength development, is, on average, at least 1, 2, 5, 7, 10, 12,
15, 20, or 25% greater than the strength without the carbon dioxide
dose, and is sufficient for the use for which the mix is intended.
In certain embodiments, an alternative or additional marker other
than early strength development, such as a value from calorimetry
as described elsewhere herein, may be used instead of or in
addition to early strength measurements, for example, to determine
the desired or optimal dose of carbon dioxide and/or dosing
conditions. The carbon dioxide may be delivered as a single dose or
multiple doses, and at any suitable rate or in any suitable form,
as described elsewhere herein. The SCM can be any suitable SCM. In
certain embodiments, the SCM is fly ash. In certain embodiments,
the SCM is slag. In certain embodiments, the SCM-concrete mix is
delivered to a job site in a ready mix truck, and the carbon
dioxide is applied to the mix at the batching site, en route to the
job site, or at the job site, or any combination thereof. In
certain embodiments, the carbon dioxide is gaseous carbon dioxide.
In certain embodiments, the carbon dioxide is dissolved in mix
water. In certain embodiments, the carbon dioxide is solid carbon
dioxide. In certain embodiments, a combination of gaseous carbon
dioxide and carbon dioxide dissolved in mix water is used.
[0261] In certain embodiments, the invention provides a method for
increasing the maximum amount (proportion) of SCM that may be used
in an SCM-concrete mix, thus increasing the overall acceptable
range of amounts (proportions) of SCM for the SCM-concrete mix, by
exposing an SCM-concrete mix that contains a proportion of SCM that
would normally be higher than the acceptable proportion due to
effects on early strength development, to a dose of carbon dioxide
sufficient to modulate, e.g., accelerate, early strength
development of the mix to a level at which the mix may be used for
its normal purposes. In certain embodiments, the maximum acceptable
proportion of SCM in the mix is increased by carbonation by at
least 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 9, 10, 11, 12,
13, 14, 15, 16, 17, 18, 19, or 20% bwc and/or not more than 1, 1.5,
2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,
18, 19, 20, or 25% bwc, over the maximum acceptable proportion of
SCM without carbonation. The dose of carbon dioxide to the mix can
be not more than 2.0, 1.5, 1.2, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4,
0.3, 0.2, 0.1, or 0.05% carbon dioxide bwc, and/or not less than
2.5, 2.0, 1.5, 1.2, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or
0.1% carbon dioxide bwc. The SCM can comprises at least 1, 2, 3, 4,
5, 6, 7, 8, 9, 10, 12, 15, 20, or 30% of the mix, and/or not less
than 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 30, 40, or 50% of the
mix. The dose can be such that the early strength development of
the mix, e.g., the strength at 8, 12, 16, 20, or 24 hours, or any
other suitable time point for early strength development, is, on
average, at least 1, 2, 5, 7, 10, 12, 15, 20, or 25% greater than
the strength without the carbon dioxide dose. In certain
embodiments, an alternative or additional marker other than early
strength development, such as a value from calorimetry as described
elsewhere herein, may be used instead of or in addition to early
strength measurements, for example, to determine the desired or
optimal dose of carbon dioxide and/or dosing conditions. The carbon
dioxide may be delivered as a single dose or multiple doses, and at
any suitable rate or in any suitable form, as described elsewhere
herein. The SCM can be any suitable SCM. In certain embodiments,
the SCM is fly ash. In certain embodiments, the SCM is slag. In
certain embodiments, the SCM-concrete mix is delivered to a job
site in a ready mix truck, and the carbon dioxide is applied to the
mix at the batching site, en route to the job site, or at the job
site, or any combination thereof. In certain embodiments, the
carbon dioxide is gaseous carbon dioxide. In certain embodiments,
the carbon dioxide is dissolved in mix water. In certain
embodiments, the carbon dioxide is solid carbon dioxide. In certain
embodiments, a combination of gaseous carbon dioxide and carbon
dioxide dissolved in mix water is used.
[0262] In certain embodiments, the invention provides a method for
accelerating the early strength development of an SCM-concrete mix,
thus accelerating aspects of a job in which the SCM-concrete mix is
used that require a certain strength before a next step may be
taken (such as removing molds, adding a level of concrete, and the
like), by exposing the SCM-concrete mix to a dose of carbon dioxide
sufficient to modulate, e.g., accelerate, early strength
development of the mix to a level at which the aspect of the job
may be accelerated. The dose of carbon dioxide to the mix can be
not more than 2.0, 1.5, 1.2, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4,
0.3, 0.2, 0.1, or 0.05% carbon dioxide bwc, and/or not less than
2.5, 2.0, 1.5, 1.2, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or
0.1% carbon dioxide bwc. The dose can be such that the early
strength development of the mix, e.g., the strength at 8, 12, 16,
20, or 24 hours, or any other suitable time point for early
strength development, is, on average, at least 1, 2, 5, 7, 10, 12,
15, 20, 25, 30, 35, or 40% greater than the strength without the
carbon dioxide dose. The SCM can comprises at least 1, 2, 3, 4, 5,
6, 7, 8, 9, 10, 12, 15, 20, or 30% of the mix, and/or not less than
2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 30, 40, or 50% of the mix.
In certain embodiments, an alternative or additional marker than
early strength development, such as a value from calorimetry as
described elsewhere herein, may be used instead of or in addition
to early strength measurements, for example, to determine the
desired or optimal dose of carbon dioxide and/or dosing conditions.
The carbon dioxide may be delivered as a single dose or multiple
doses, and at any suitable rate or in any suitable form, as
described elsewhere herein. The SCM can be any suitable SCM. In
certain embodiments, the SCM is fly ash. In certain embodiments,
the SCM is slag. In certain embodiments, the SCM-concrete mix is
delivered to a job site in a ready mix truck, and the carbon
dioxide is applied to the mix at the batching site, en route to the
job site, or at the job site, or any combination thereof. In
certain embodiments, the carbon dioxide is gaseous carbon dioxide.
In certain embodiments, the carbon dioxide is dissolved in mix
water. In certain embodiments, the carbon dioxide is solid carbon
dioxide. In certain embodiments, a combination of gaseous carbon
dioxide and carbon dioxide dissolved in mix water is used.
C. Control Mechanisms
[0263] The methods and apparatus described herein may include one
or more control mechanisms, e.g., automatic control mechanisms, to
modulate one or more aspects of the mix and carbonation operation,
such as to modulate the contact of the cement mix, e.g., hydraulic
cement mix with carbon dioxide and/or other components, such as one
or more admixtures or water, as well as other aspects of the
operation of the mixer, such as worker safety requirements, cooling
of the cement mix, e.g., hydraulic cement mix, and the like. It
will be appreciated that modulation may be achieved by human
operators who control the necessary valves and the like to achieve
a desired carbon dioxide exposure and/or other characteristic of
the carbonated cement mix, but in general automatic control
mechanisms are employed. The control may be based on any suitable
parameter, such as feedback regarding one or more characteristics
of the mix operation, timing, which may be a predetermined timing,
or a combination thereof.
[0264] Control systems and mechanisms can apply to a stationary
mixer in a precast concrete plant or other central mixing facility.
Alternatively, it can apply to a ready mix concrete truck that
facilitates mixing through rotation of its drum. The mix operation
can be a dry cast or wet cast operation; for example, the ready mix
concrete truck will be a wet cast, while precast may be wet cast or
dry cast.
[0265] A simple form of control is based on timing alone. Thus, in
certain embodiments, the methods include modulating the flow of
carbon dioxide to the cement mix, e.g., hydraulic cement mix
according to a certain timing. The timing may be controlled by a
controller that is connected to a cement mix, e.g., hydraulic
cement mix apparatus and that senses when the apparatus has begun
or stopped a stage of operation, and that modulates carbon dioxide
flow accordingly, e.g., starts or stops flow. Thus in certain
embodiments, carbon dioxide flow is begun when one or more
components of a cement mix, e.g., hydraulic cement mix have been
deposited in a mixer, continues for a certain predetermined time at
a certain predetermined flow rate, then stops. The stage of
operation of the cement mix, e.g., hydraulic cement mix apparatus
may be determined by the programming of the controller or of
another controller to which the controller is operably connected,
or it may be determined by one or more sensors which monitor
positions of components of the apparatus, flow, and the like, or a
combination thereof.
[0266] Typically, however, control systems and mechanisms of the
invention include feedback mechanisms where one or more
characteristics of the cement mix, e.g., hydraulic cement mixture
and/or apparatus or its environment is monitored by one or more
sensors, which transmit the information to a controller which
determines whether one or more parameters of the mix operation
requires modulation and, if so, sends the appropriate output to one
or more actuators to carry out the required modulation. The
controller may learn from the conditions of one batch to adjust
programming for subsequent batches of similar or the same mix
characteristics to optimize efficiency and desired characteristics
of the mix.
[0267] In order to achieve a desired efficiency of carbon dioxide
uptake in the cement mix, e.g., hydraulic cement mix, to ensure
desired characteristics such as flow characteristics, strength, and
appearance, and/or to ensure worker safety, various aspects of the
mix operation, the mixer, the cement mix, e.g., hydraulic cement
mix, and the environment of the mixer may be monitored, the
information from the monitoring processed, and adjustments made in
one or more aspects of the mix operation in order to achieve the
desired result. Thus, in certain embodiments, one or more sensors
may be used to provide input to a controller as to various
conditions related to the desired characteristics; the controller
processes the inputs and compares them to predetermined parameters
of operation and, if corrections in the process are necessary, the
controller then sends output to one or more actuators in order to
bring the system back toward the desired condition.
[0268] In particular embodiments, the invention provides control
systems for controlling the carbonation of a cement mix, e.g.,
hydraulic cement mix in a mixer by use of one or more sensors
monitoring one or more of weight of the cement used in the mix,
carbon dioxide concentration of the atmosphere inside and/or
outside the mixer, temperature of the cement mix, e.g., hydraulic
cement mix or a component in contact with the cement mix, e.g.,
hydraulic cement mix, rheology of the mix, and/or moisture content
of the mix, where the one or more sensors send input to a
controller which processes the information received from the one or
more sensors by comparing the input to one or more predetermined
parameters and, if necessary, sends output to one or more actuators
to adjust carbon dioxide flow rate, water addition, or admixture
addition, or to perform other functions such as to sound an alarm
if carbon dioxide levels exceed safe levels. In addition, certain
operations, such as cooling of the cement mix, e.g., hydraulic
cement mix, may be performed after the mixing is complete. The
controller can learn from one batch to adjust conditions for a
subsequent batch of the same or similar composition. Further levels
of control may be used, such as a central controller that receives
information from a plurality of mix operations in a plurality of
locations regarding one or more aspects of each operation, and
processes the information received from all mix operations to
improve performance at the various operations; thus, large amounts
of information can be used to improve performance at a variety of
sites.
[0269] In the mixing operation, components of the cement mix, e.g.,
hydraulic cement mix, e.g., cement, aggregate, and water, are added
to the mixer, and mixing commences. In some cases some components,
such as aggregate, may have a sufficient water content, e.g., from
exposure to wet weather conditions, that additional water is not
added before mixing commences. In some cases, as described
elsewhere herein, water or other components may be added in a
staged manner. At some point before, during, or after the process
of addition of components or mixing, carbon dioxide flow is
initiated from a source of carbon dioxide to the mixer. In some
cases, part or all of the carbon dioxide will be included in the
mix water. In some cases, the carbon dioxide flow will be gaseous;
in other cases, the carbon dioxide flow comprises a mixture of
gaseous and solid carbon dioxide. Additional components, such as
admixtures, may be added to the cement mix, e.g., hydraulic cement
mix as well at any point in the operation. The carbon dioxide is
subsumed into the mixing cement mix, e.g., hydraulic cement mix and
begins reaction with the mix components; any carbon dioxide that is
not taken up by the cement mix, e.g., hydraulic cement mix fills
the head space of the mix container. Since typical mixers are not
airtight, if the rate of carbon dioxide flow to the mixer exceeds
the rate of uptake into the cement mix, e.g., hydraulic cement mix,
at some point the head space in the mixer will be full of carbon
dioxide and excess carbon dioxide will exit the mixer from one or
more leak points. Thus, the carbon dioxide content of the
atmosphere inside the mixer or, more preferably, outside the mixer,
e.g., at one or more leak points, may be monitored to provide an
indication that the rate of carbon dioxide addition is exceeding
the rate of carbon dioxide uptake. In addition, carbon dioxide
levels in areas where workers are likely to be may also be
monitored as a safety precaution. The reaction of carbon dioxide
with the hydraulic cement is exothermic, thus the temperature of
the cement mix, e.g., hydraulic cement mix rises; the rate of
temperature rise is proportional to the rate of carbon dioxide
uptake and the overall temperature rise is proportional to total
carbon dioxide uptake for a given mix design. Thus, the temperature
of the cement mix, e.g., hydraulic cement mix, or the temperature
of one or more portions of the mix container or other equipment
that are in contact with the mix, may be monitored as an indication
of rate and extent of carbon dioxide uptake into the cement mix,
e.g., hydraulic cement mix. Carbonation of components of the cement
mix, e.g., hydraulic cement mix may produce a change in the flow
characteristics, i.e., rheology, of the cement mix, e.g., hydraulic
cement mix, which can be undesirable in certain applications, e.g.,
in wet cast applications such as in a ready mix truck. Thus, the
rheology of the cement mix, e.g., hydraulic cement mix may be
monitored. In addition, carbonation may affect the moisture
characteristics of the cement mix, e.g., hydraulic cement mix,
which may lead to undesirable characteristics, and moisture content
of the mix may be monitored as well.
[0270] The invention also provides a network of mix systems with
one or more sensors and, optionally, controllers, that includes a
plurality of mix systems, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, or
more than 10 mix systems with one or more sensors and, optionally,
controllers, each of which transmits data from their respective
locations and mix conditions to a central controller, which learns
from the overall data from all the mix systems and provides updated
and modified mix instructions to the various mix systems in the
network based on this information. In this way the operation of
each individual mix system within the network can be optimized
based on information from all the other mix systems in the network.
Thus, timing and extent of carbon dioxide delivery, admixture type
and amount, water amount and timing and delivery, and other factors
may be optimized for one site before it has even begun its first
batch, based on historical information from other sites, and all
sites may undergo continual improvement in optimization as the
sensors, and, optionally, controllers in the network continually
gain more information and feed it to the central controller.
[0271] Thus, in certain embodiments the methods and/or apparatus
may include feedback mechanisms by which one or more
characteristics of the type of mixer apparatus, cement mix, e.g.,
hydraulic cement mix, a gas mixture in contact with the cement mix,
e.g., hydraulic cement mix and inside or outside of the mixer, a
component of the cement mix, e.g., hydraulic cement mix production
apparatus, a component exposed to the cement mix, e.g., hydraulic
cement mix, or the environment of the mixer, is monitored and the
information is used to modulate the exposure of the cement mix,
e.g., hydraulic cement mix to carbon dioxide, one or more
admixtures, water, or other components, in the current mix and/or
in subsequent mixes. Characteristics such as carbon dioxide content
monitored inside and/or outside the mixer, and/or temperature of
the mix monitored inside the mixer or outside of the mixer, of a
component in contact with the cement mix, e.g., hydraulic cement
mix, e.g., a surface of the mixer such as the outer surface of the
mixer, and/or position or state of operation of a component of the
cement mix, e.g., hydraulic cement mix production apparatus, may be
used to determine when to modulate carbon dioxide addition, e.g.,
to start or to stop or slow carbon dioxide addition. Certain safety
monitoring may also be done, e.g., monitoring of areas outside the
mixer for carbon dioxide levels to ensure worker safety.
[0272] In general, feedback systems include one or more sensors for
monitoring one or more characteristics and sending input to a
controller, which receives the input from the sensors, processes
it, and, if necessary, sends output, based on the processing, to
one or more actuators that is configured to alter some aspect of
the exposure of the cement mix, e.g., hydraulic cement mix to
carbon dioxide, water, admixture, or some other aspect of the
operation of the cement mix, e.g., hydraulic cement mix apparatus.
In the simplest case, a human operator may manually begin carbon
dioxide exposure by adjusting a valve, then may monitor a
characteristic by using one or more sensors, e.g., a handheld
temperature sensor that is pointed at the drum of a readymix truck,
and/or a simple timer, and halt the supply of carbon dioxide gas
when a certain temperature or a certain time is reached. However,
in general automatic feedback mechanisms are used.
[0273] Sensors
[0274] Suitable sensors for use in control systems include
temperature sensors, carbon dioxide sensors, rheology sensors,
weight sensors (e.g., for monitoring the exact weight of cement
used in a particular batch), moisture sensors, other gas sensors
such as oxygen sensors, pH sensors, and other sensors for
monitoring one or more characteristics of a gas mixture in contact
with the cement mix, e.g., hydraulic cement mix, a component of the
cement mix, e.g., hydraulic cement mix production apparatus, a
component exposed to the cement mix, e.g., hydraulic cement mix, or
some other aspect of the mix operation. Sensors also include
sensors that monitor a component of the cement mix, e.g., hydraulic
cement mix apparatus, such as sensors that detect when mixing has
begun, when components of a cement mix, e.g., hydraulic cement mix
have been added to a mixer, mass flow sensors, flow rate or
pressure meter in the conduit, or other suitable sensors.
[0275] Cement Weight Scale Sensor
[0276] A cement weight scale sensor can be used to transmit
information to the controller concerning the mass of cement that
will be in a given mixture in the mixer. Since the CO.sub.2 is
dosed in proportion to the mass of cement, this weight is important
for determining the correct dose to achieve the desired outcomes.
The cement mass is also used to scale the size of a given batch,
given that a mixture could vary in relation to a default size such
as a full batch (100%) or a quarter batch (25%), or any other batch
size. In some cases the batch could even exceed 100%. This batch
size can also be used to determine the head (free) space in the
mixer so that it can be rapidly filled with CO.sub.2 without
creating an overpressure by delivering more than the headspace will
allow. Once the head space is full, the flow rate can be reduced to
match the uptake rate of the cement.
[0277] Carbon Dioxide Sensors
[0278] One or more CO.sub.2 sensors may be used to minimize waste,
i.e., to increase the efficiency of carbon dioxide uptake, and/or
to ensure worker safety. The CO.sub.2 sensors work by measuring the
CO.sub.2 content of the air around the outside of the mixer and/or
inside the mixer. Alternatively, or additionally, one or more
sensors may be located inside the mixer and sense the carbon
dioxide content of the gas in the mixer and send a signal to a
controller. The sensors may be any sensor capable of monitoring the
concentration of carbon dioxide in a gas and transmitting a signal
to the controller based on the concentration, and may be located in
any convenient location or locations inside or outside the mixer;
if inside, preferably in a location such that the sensor is not
subject to fouling by the cement mix, e.g., hydraulic cement mix as
it is being mixed or poured. In addition to, or instead of, carbon
dioxide sensors inside the mixer, one or more such sensors may be
located outside the mixer to sense the carbon dioxide content of
overflow gas escaping the mixer and send a signal to a controller.
In either case, a certain range or ranges, or a cutoff value, for
carbon dioxide content may be set, and after the carbon dioxide
content of the mixer and/or overflow gas reaches the desired range,
or goes above the desired threshold, carbon dioxide delivery, or
some other aspect of the cement mix, e.g., hydraulic cement mix
apparatus, may be modulated by a signal or signals from the
controller to an actuator or actuators. For example, in certain
embodiments a carbon dioxide sensor may be located outside the
mixer and when carbon dioxide content of the overflow gas reaches a
certain threshold, such as a carbon dioxide concentration that
indicates that the gas mixture in contact with the cement mix,
e.g., hydraulic cement mix is saturated with carbon dioxide, carbon
dioxide delivery to the cement mix, e.g., hydraulic cement mix,
e.g., inside the mixer is halted or slowed by closing a valve,
partially or completely, in the conduit from the carbon dioxide
source to the mixer.
[0279] In particular, for minimizing waste, one or more sensors can
be placed in the areas where leaks are most likely to occur (e.g.,
around doors, etc.). The sensor or sensors may be positioned so
that leaking carbon dioxide is most likely to pass in their
vicinity, e.g., since carbon dioxide is more dense than air,
positioning below a likely leak point is more desirable than
positioning above a likely leak point. When the gas is delivered at
a rate much greater than capacity of the cement to absorb the
CO.sub.2 it is more likely to spill out of the mixer at a leak
point and be detected by a gas sensor. Leaks would be a normally
occurring event when there is too much gas delivered to the mixer
given that the mixer is not completely gas tight according to the
nature of the machine. A CO.sub.2 leak would occur when the
CO.sub.2 has been delivered too quickly. Given that CO.sub.2 is
heavier than air there would be, in general, a certain amount of
CO.sub.2 that can be delivered to the mixer wherein the incoming
CO.sub.2 gas would displace air that initial was sitting in the
mixer. Once the air has been displaced an delivery of additional
gas would displace previously delivered carbon dioxide or otherwise
be immediately spilled from the mixer. Sensors that feed into a
dosing logic system would preferably be placed in locations
immediately beside the mixer leak points. If the one or more
sensors read that the CO.sub.2 content in the vicinity exceeds a
preset threshold level (e.g. a defined baseline), the system will
adjust the CO.sub.2 flow rate and/or delivery time, e.g., to
decrease or eliminate additional overspill in the present batch or
to eliminate the overspill in a future mixing cycle. The logic can
co-ordinate a filling rate of the mixer space that is proportional
to the uptake rate of CO.sub.2 by the cement.
[0280] For worker safety, if a carbon dioxide delivery causes the
carbon dioxide concentration in areas around the mixer normally
accessed by workers to exceed a maximum value (such as indicated by
OSHA), the controller can signal for a system shut down wherein all
the valves can be closed and, typically, an alarm can be sounded as
a safety measure. Sensors that feed into a safety system can be
placed at various distances from the mixer depending on the
proximity requirements for workers to the mixer.
[0281] Temperature Sensors
[0282] One or more sensors may be used to monitor the temperature
of the mix inside or outside of the mixer and/or of a component in
contact with the cement mix, e.g., hydraulic cement mix and/or of
the mixer, which is indicative of carbonation and/or other
reactions due to the addition of the carbon dioxide, and carbon
dioxide addition modulated based on this temperature or
temperatures monitored by the sensor(s). One or more temperature
sensors may be located to monitor the temperature of the cement
mix, e.g., hydraulic cement mix, for example, within the mixer, or
at a site distal to the mixer such as a holding site or transport
site for the cement mix, e.g., hydraulic cement mix. Such a site
may be, e.g., a feedbox for a pre-cast operation, or a belt or
other transport mode, or a wheelbarrow or other site for
transporting or storing concrete from a ready-mix truck. One or
more temperature sensors may be located to monitor the temperature
of a component that is in contact with the cement mix, e.g.,
hydraulic cement mix, e.g., the drum of the mixer. Any suitable
temperature sensor may be used. For example, an infrared
temperature sensor, such as a mounted or handheld sensor, may be
used to monitor the temperature of the drum of a ready-mix truck to
which carbon dioxide is added, and when a certain temperature is
reached or range of temperatures achieved, the addition of the
carbon dioxide inside the drum may be modulated.
[0283] The temperature or range of temperatures at which the carbon
dioxide exposure is modulated may be a predetermined temperature or
range, based on a temperature known to be associated with one or
more undesirable characteristics, e.g., reduced strength,
workability loss, poor compactability performance, hardening in the
mixer, etc. In some cases it may be an absolute temperature or
range. More preferably, it is a temperature or range that is
determined in reference to an initial temperature, such as an
initial temperature of the cement mix, e.g., hydraulic cement mix
or a component in contact with the mix before addition of carbon
dioxide. In certain embodiments, the temperature or range is at
least 10, 15, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 35, 40,
45, or 50.degree. C. above the initial temperature, or 10-50,
10-40, 10-30.degree. C. above the initial temperature, and with
that range a threshold may be set, which may vary from batch to
batch depending on the desired carbonation of the concrete mix or
other characteristics. In certain cases, e.g., where warm starting
materials are used, the temperature is kept unchanged from the
starting temperature, or kept within 0-5.degree. C. of the starting
temperature. In some case, an absolute maximum temperature is set
and the control system is configured to keep the mix below the
maximum temperature. The sensor can also be used to monitor rate of
temperature rise and the controller can adjust the flow rate and/or
delivery time if the rate is too high or too low. Test data
indicates that, for a constant flow, the carbon uptake is
proportional to temperature increase detected immediately after
carbonation for a given mix. An in-situ temperature measurement may
be used to model the real-time total carbon dioxide uptake of the
cement mix, e.g., hydraulic cement mix with respect to previously
collected calibration data.
[0284] Rheology Sensors
[0285] In an operation in which flowability of the cement mix is
important, e.g., a wet cast operation, one or more rheology sensors
may be used. A rheometer can be mounted inside the mixer to measure
the workability of the cement mix, e.g., hydraulic cement mix.
CO.sub.2 can reduce the workability of the fresh cement mix, e.g.,
hydraulic cement mix, and the rheometer can be used to monitor the
workability loss. At a certain preset minimum threshold of
workability, one or more actions may be triggered, such as
modulation of the rate of CO.sub.2 flow to the mixer, addition of
admixture, and/or addition of additional water, to restore
workability to a desired level. A rheometer can also monitor the
workability of concrete in a ready mix concrete truck while it is
in transit and adjust CO.sub.2/admixture doses on subsequent
mixtures produced at the batching plant, or even adjust an
admixture dose delivered in the drum truck itself.
[0286] Moisture Sensors
[0287] One or more moisture sensors may be used. The moisture
sensor is used to monitor the moisture in the cement mix, e.g.,
hydraulic cement mix during the mixing cycle. As CO.sub.2 is taken
up by the cement mix, e.g., hydraulic cement mix, the apparent
moisture can be reduced and result in a drier looking product.
Therefore the mix moisture may need to be increased to maintain the
desired product appearance. If the moisture reaches a minimum
threshold value, the CO.sub.2 can be modulated, e.g., reduced or
shut off so the mix is not released in an unacceptably dry
condition. The sensor also monitors the moisture decrease with
respect to CO.sub.2 uptake and can adjust the flow rate and/or
delivery time if the rate becomes too high or too low. The moisture
sensor can also trigger the addition of supplemental mix water at
any point in the mixing process. In addition, one or more moisture
sensors may be used to determine the moisture content of one or
more components of the cement mix, e.g., hydraulic cement mix
before the components are mixed; for example, a moisture sensor may
be used to determine the moisture content of aggregate, which may
be exposed to weather conditions leading to water pickup. In the
case of an operation where carbon dioxide is added via mix water as
well as by gas or liquid, such information may be used to adjust
the relative amount of carbon dioxide added via gas or liquid, to
compensate for the fact that less mix water will be used due to the
moisture content of the aggregate.
[0288] Other Sensors
[0289] One or more sensors may monitor conditions of the cement
mix, e.g., hydraulic cement mix apparatus and send a signal to a
controller. For example, one or more sensors may monitor when all
desired components of the cement mix, e.g., hydraulic cement mix
are in the mixer and mixing, and the controller may send a signal
to an actuator, such as a controllable valve, to begin flow of
carbon dioxide. The carbon dioxide flow may continue for a
predetermined time, or may be modulated according to further
feedback, such as described above.
[0290] Other conditions may be monitored, as well, such as pressure
conditions in one or more lines; for example, in a system where
liquid carbon dioxide is delivered to the mixer, sensors may be
employed to control dry ice formation between the nozzle and
solenoid as well as to confirm pre-solenoid pressure is maintained
to ensure the line remains liquid.
[0291] Any combination of one or more sensors inside or outside the
mixer, and/or inside or outside the mix, may be used to monitor
cement binder weight, cement binder location, carbon dioxide
content, temperature, rheology, moisture content, pH, other
characteristics, or a combination thereof, and feedback loops to
modulate the addition of carbon dioxide based on the information
provided by these sensors may be used; such loops may include
automatic or manual adjustments, or both. In certain embodiments,
sensors monitor the cement binder addition time and/or dust
collector system operation time, as in some mixers a fan is run
after the powders go in to prevent excessive dust, and these should
be turned off so that added carbon dioxide is not removed during
this time.
[0292] Thus, in certain embodiments the invention provides a method
or apparatus for producing carbonated cement mix, e.g., hydraulic
cement mix that includes a control system that includes at least
one sensor selected from the group consisting of a carbon dioxide
sensor, a temperature sensor, a rheology sensor, and a moisture
sensor. In certain embodiments the invention provides a method or
apparatus for producing carbonated cement mix, e.g., hydraulic
cement mix that includes a control system that includes at least
two sensors selected from the group consisting of a carbon dioxide
sensor, a temperature sensor, a rheology sensor, and a moisture
sensor. In certain embodiments the invention provides a method or
apparatus for producing carbonated cement mix, e.g., hydraulic
cement mix that includes a control system that includes at least
three sensors selected from the group consisting of a carbon
dioxide sensor, a temperature sensor, a rheology sensor, and a
moisture sensor. In certain embodiments the invention provides a
method or apparatus for producing carbonated cement mix, e.g.,
hydraulic cement mix that includes a control system that includes a
carbon dioxide sensor, a temperature sensor, a rheology sensor, and
a moisture sensor. The methods and apparatus can further include
one or more actuators for adjusting some aspect of the mix
operation, for example carbon dioxide flow to the mixer, or
admixture flow to the mixer, and a controller that receives signals
from the sensor or sensors, processes them to determine if
modulation of the mix operation is required, and, if so, transmits
a signal to an actuator or actuators to carry out the
modulation.
[0293] Actuators
[0294] The actuator or actuators may be, e.g., one or more valves,
such as solenoid valve, in one or more conduits supplying a
component, such as carbon dioxide, to the mixer, as described
elsewhere herein. An actuator for CO.sub.2 delivery can be, e.g., a
delivery manifold with, e.g. gas temperature sensor, gas pressure
gauge, modulating control valve, open/close solenoid and orifice
plate assembly. These components can all be combined in a singular
unit, i.e. a flow controller. In certain embodiments, in addition
to or alternatively to, a gas delivery system, one or more
actuators for controlling delivery of carbonated mix water, as
described herein, may be used. Such actuators may include, e.g.,
actuators to control charging mix water with carbon dioxide and/or
actuators to control delivery of carbon dioxide-charged water to
the mixer. Similarly, an actuator controlling water delivery to the
mix may be under the control of the controller, as may be an
actuator controlling delivery of one or more admixtures to the mix.
In addition, an actuator may include a relay switch attached to
dust collector power source to shut off mixer dust collector during
CO.sub.2 delivery (if necessary). In general, the modulation of the
carbon dioxide exposure will be an increase or decrease in
exposure, such as a decrease in flow rate of carbon dioxide gas to
the mixer. In certain embodiments, the modulation is halting the
flow of carbon dioxide gas to the mixer.
[0295] Thus, in certain embodiments the invention provides a method
or apparatus for producing carbonated cement mix, e.g., hydraulic
cement mix that includes a control system that includes at least
one actuator for controlling at least one action selected from the
group consisting of a carbon dioxide flow to the mixer, water flow
to the mixer, and admixture flow to the mixer. In certain
embodiments the invention provides a method or apparatus for
producing carbonated cement mix, e.g., hydraulic cement mix that
includes a control system that includes at least two actuators for
controlling at least two actions selected from the group consisting
of a carbon dioxide flow to the mixer, water flow to the mixer, and
admixture flow to the mixer. In certain embodiments the invention
provides a method or apparatus for producing carbonated cement mix,
e.g., hydraulic cement mix that includes a control system that
includes an actuator for controlling carbon dioxide flow to the
mixer, an actuator for controlling water flow to the mixer, and an
actuator for controlling admixture flow to the mixer.
[0296] Other actuators, such as actuators that control one or more
aspects of hydraulic cement production, such as timing of mixing,
delivery of cooling input such as ice or liquid nitrogen,
activation of an alarm, and the like, may also be used as
appropriate.
[0297] Controller
[0298] The control systems used in methods and apparatus can
include a controller that receives inputs from the one or more
sensors, processes them by comparing them to preset values for
achieving the desired result, and, as necessary, sends outputs to
the one or more actuators to move the system toward the desired
result.
[0299] The controller may be, e.g., an electronic circuit or a
programmable logic controller, located either on-site with the
mixer or off-site, e.g., as part of a computer network. For
example, the controller may be a Programmable Logic Controller
(PLC) with a Human Machine Interface (HMI), for example a touch
screen and onboard telemetry computer. The controller can be
integrated into the overall mixer controller or it can be a
separate unit that receives inputs from the mixer controller as
appropriate.
[0300] An exemplary set of operations for a controller in response
to inputs from various sensors and giving outputs to various
actuators is illustrated below.
[0301] The system can include the following components: 1)
Programmable Logic Controller (PLC) with attached Human Machine
Interface (HMI), for example a touch screen and onboard telemetry
computer. 2) Gas delivery manifold with, e.g., gas temperature
sensor, gas pressure gauge, modulating control valve, open/close
solenoid and orifice plate assembly. These components can all be
combined in a singular unit, i.e. a flow controller. 3) Cement
weight scale feeding into a concrete mixer to measure quantity of
cement used in a batch. This quantity is used logically to
determine the CO.sub.2 dose based on cement content (further
information below). 4) Proximity switch to trigger the delivery of
CO.sub.2 into the mixer 5) Relay switch attached to dust collector
power source to shut off mixer dust collector during CO.sub.2
delivery (if necessary). 6) One or more CO.sub.2 sensors positioned
around the mixer used to monitor carbon dioxide gas concentration
outside the mixer. The data can be used logically to minimize
wastage by controlling flow or monitor safety (further information
below). 7) Concrete temperature sensor in or on mixer used to
monitor the concrete temperature during the carbonation treatment.
The data can be used logically to control the CO.sub.2 dose as well
as the flow rate (further information below). 8) Moisture sensor
used to monitor concrete moisture in the mixer. This information
can be used to logically control the CO.sub.2 dose (further
information below). 9) Concrete rheology sensor to monitor the
consistency of the concrete. Information about the workability of
the concrete can logically be used to signal admixture delivery or
process end points. Not all of these components need be present,
depending on the needs of the mix operation. For example, in a dry
cast operation, a rheology sensor may not be used.
[0302] The steps of operation of the system are as follows:
[0303] 1. A PLC is programmed, for example, through the HMI, to
apply carbon dioxide treatment to a first batch. Process threshold
settings for aspects such as CO.sub.2 concentration in the air at a
leak point and/or at a worker area, concrete temperature and/or
rate of temperature change, concrete moisture and/or rate of
moisture change, concrete rheology can be input at this time.
[0304] 2. Batching starts by a signal from the mixing controller to
the mixer. This follows logically after the previous step. The
mixer controller software can communicate batch information to the
PLC.
[0305] 3. Materials are added to mixer (e.g. aggregates). This
follows logically after the previous step as part of normal
practice.
[0306] 4. The cement is weighed. This follows logically after the
previous step as part of normal practice. A cement mass (weight)
sensor determines mass (weight) of cement used in the batch and
feeds information to the PLC
[0307] 5. The PLC makes a calculation to determine the required gas
flow. This follows logically from an earlier step. The PLC
calculates the amount of gas required for delivery to the current
mix based upon a percentage dosage rate of gas mass to cement mass.
The PLC calculation may refer to a predetermined set point. It may
alternatively, or in addition, call upon historical data of
previous combinations of mix size, mix type and CO.sub.2 dosage
rate, either from the mix site at which the current batch is being
mixed, or from other mix sites, or a combination thereof. It can
use information (either input or detected) about the batch size,
cement mass, mix type and mixer volume. For example, it can use
information about cement type or origin to determine whether,
which, and/or how much admixture should be employed. The PLC can
accept information required for calculations from sources including
user input into the HMI, communication with the mixer controller
software, and the cement mass sensor. The PLC calculations will
depend upon acquiring all of the required data which can come from,
e.g., the HMI in step 1, mix controller software in step 2, and/or
the cement mass sensor in step 4.
[0308] 6. Cement is dropped into the mixer. This follows logically
after the previous step. The time that cement enters the mixer is
detected. A proximity sensor can detect the cement deposit in the
mixer through a physical movement (e.g. the opening of a door or
gate). Alternatively, the cement addition time can be supplied
synchronously from the mixer controller software. The time that the
cement is placed into mixer is transmitted to the PLC.
[0309] 7. The PLC starts the gas delivery. This can be concurrent
with the previous step, at some predetermined time after the
previous step, or even before the previous step, if it is desired
to replace some or all of the air in the mixer with CO.sub.2 prior
to deposition of the cement. The PLC can send a signal to the mixer
dust collector to be turned off for all or part of the CO.sub.2
delivery or otherwise coordinated with some aspect of the gas
delivery. The PLC sends signal to the solenoid in the CO.sub.2
delivery system to open either in coordination with the cement
insertion or at some time before or after the insertion.
[0310] 8. The PLC surveys the sensors for any process conditions
that signal the CO.sub.2 delivery is to change/end according to
preset conditions or for other measurable aspects. This follows
logically after the previous step. A) Temperature sensor--the
concrete temperature exceeds a threshold value or rate that can be
set for correlation to a maximum allowable temperature rise or a
target temperature rise. B) CO.sub.2 leak sensors--the CO.sub.2
sensors at the significant leak points of the mixer have detected a
CO.sub.2 content that exceeds a preset threshold or a relative
value above a baseline measurement. C) CO.sub.2 safety sensors--the
CO.sub.2 sensors monitoring the CO.sub.2 content of the air in the
general vicinity of the mixer have reached a threshold value. There
can also be an oxygen sensor measuring the oxygen content of the
air. These sensors are located in areas accessed by workers around
the machine as opposed to leaks immediately from the mixer. D)
Moisture sensor--the moisture content of the concrete has reached
an absolute threshold with respect to a set point or otherwise has
passed a relative measure with respect to the batch at hand. For
example, a condition might acknowledge that the moisture content of
the concrete inherently varies from batch to batch but would search
for a decline in moisture content of, e.g., 0.5% with respect to
the measurement expected if no CO.sub.2 had been applied or the
initial measurement, etc. E) Rheology--(relevant to wet mix) the
workability of the concrete is measured and found to reach a
threshold level. F) Timer on PLC--PLC may have a predefined maximum
delivery time that may signal a stop condition in the event no
other sensors have triggered a stop.
[0311] 9. A gas flow modification condition is detected. The PLC
receives a signal from a sensor and modifies the gas delivery in
response. Follows logically from previous step. A) Any sensor may
suggest the gas input flow is modified (e.g., reduced) as a
threshold value is neared rather than simply attained or crossed.
B) Temperature Sensor--if the sensor detects an increase in the
temperature of the concrete that is greater than expected then a
signal can be sent by the PLC to reduce the rate of input of carbon
dioxide. Conversely, if the rate of temperature increase is lower
than expected then the PLC can increase the rate input of carbon
dioxide. In addition or alternatively, if a certain threshold
temperature is reached, carbon dioxide delivery may be halted. C)
CO.sub.2 leak sensors--if the sensors detect an increase in
CO.sub.2 concentration at the mixer leak points a signal can be
sent to the PLC, which reduces the input of carbon dioxide. For
example, the leaking can be an indication that the head space of
the mixer has been filled with CO.sub.2 and any further addition
will result in leaks or overspill. The CO.sub.2 input may be
reduced to a rate that is in proportion to the projected absorption
rate of the carbon dioxide into the cement. Thereby any gas that is
absorbed into the concrete is in turn replaced with new gaseous
CO.sub.2 to maintain an overall amount of gas in the mixer. D)
Rheology sensor--if the sensor detects a decrease, e.g., a rapid
decrease in the workability of the concrete, a signal can be sent
by the PLC to reduce carbon dioxide input. Conversely, if the
workability loss is less than expected, the PLC can increase the
carbon dioxide input. Other outputs from the PLC may cause addition
of admixture, water, or both to the mix.
[0312] 10. A gas delivery stop condition achieved, PLC receives
signal to stop gas delivery. Follows logically from previous step.
Solenoid is closed. Gas delivery ends.
[0313] 11. After the CO.sub.2 delivery is complete the sensors may
send signals to the controller that call for supplemental inputs to
the mixer. Follows logically from previous step. A) Temperature
sensor can detect a temperature rise that calls for the concrete
temperature to be reduced through the addition of a cooling input
such as ice or liquid nitrogen. B) Temperature sensor detects that
the target CO.sub.2 uptake of the concrete has been achieved which
may prompt the addition of an appropriate admixture. C) Moisture
sensor reading causes PLC to signal for additional mix water or
other remedial measure such as an admixture. D) Rheology sensor
input to PLC causes output for additional mix water addition, or an
admixture addition, or both, to facilitate a workability increase
or other remedial measure.
[0314] 12. Batching and mixing is complete. Concrete is released to
the remainder of the production cycle. Follows logically from
previous step.
[0315] 13. The PLC can perform calculations to learn for subsequent
batches--particularly for the next time that same or similar
combination of mix design and CO.sub.2 dosage is used. Otherwise
settings can be predicted for other CO.sub.2 dosages to apply to
that same mix design, or for smaller batches of that mix design
with the same CO.sub.2 dosage, etc. This can be concurrent with
previous step. A) The data from CO.sub.2 leak sensors can dictate
that, for a future mix, the flow rate should be reduced if there
were excessive leaks (too much gas is supplied) or increased
because there are no leaks at all (not enough gas has been
supplied) in the present mix. The PLC will make note of the updated
or recalculated gas flow setting for future use. B) Temperature
data can inform future cooling treatment usage. The PLC will make
note of the temperature response in the wake of the applied
temperature adjustment for adjustment of the cooling treatment in
future batches. For example the future cooling treatment can be
greater or lower if the current cooling treatment was found to be
inadequate. C) Temperature data can inform future kinetic
assessments of temperature rise vs time for a given combination of
mix design and gas delivery condition. D) The moisture sensor data
can inform future mix water adjustment required either to be
included as part of the initial mix water or as late addition mix
water. In the first case the total water addition might be
approached incrementally whereas later mixes can use the end point
determined in the first mix as a target setting. E) Rheological
information can inform future admix usage. The PLC can correlate a
quantified dose of admix with the response in workability metric.
The proportion of admix to aspects such as, but not limited to,
cement content, absorbed carbon dioxide (either measured directly
after the fact or approximated by temperature increase) workability
improvement can be recorded and recursively recalculated as
additional data is acquired thereby improving the admix dosing
logic. Further information regarding characteristics of the batch,
such as flowability or strength at one or more time points, water
absorption, and the like, may also be input.
[0316] 14. Telemetry data can be logged and distributed by the PLC
to a remote data storage. This can be concurrent with the end of
gas delivery (step 10) or follow from later steps if additional
information acquired after the end of delivery is part of the
transmitted information.
[0317] Exemplary mixers and control systems are illustrated in
FIGS. 1, 2, and 3. FIG. 1 shows a stationary planetary mixer, e.g.,
for use in a precast operation. The cement scale 1 includes a mass
sensor that sends data regarding the mass of cement dispensed from
the cement silo 2 to the controller 10. Proximity sensor 3 senses
when cement is released to the mixer and sends a signal to the
controller; alternatively, the mix controller (not shown) can send
a signal to the controller 10 when the cement is released. CO.sub.2
delivery may commence upon release of the cement; alternatively,
CO.sub.2 delivery may commence before or after release. CO.sub.2
sensors 8 and 9 are located at leak areas outside the mixer and
send signals regarding atmospheric CO.sub.2 content to the
controller 10. In addition, temperature sensor 6 sends signals
regarding the temperature of the concrete mix to the controller 10.
Additional sensors, such as moisture and rheology sensors, or
additional CO.sub.2 sensors in worker areas in the vicinity of the
mixer may be used (not shown) and send additional signals to the
controller. Controller 10 processes the signals and sends output to
an actuator 11 for controlling delivery of CO.sub.2 from a CO.sub.2
supply 13 via a conduit to the CO.sub.2 gas mixer inlet 7, where it
enters the mixer headspace 4 and contacts the mixing concrete 5.
For example, in a basic case, the controller 10 may send a signal
to the actuator 11 to open a valve for delivery of CO.sub.2 upon
receiving input from the proximity sensor 3 indicating that cement
has been delivered to the mixer, and send a signal to the actuator
11 to close the valve upon receiving input from one or more of the
CO.sub.2 sensors 8 and 9 or the temperature sensor 6 indicating
that the desired delivery of CO.sub.2 to the mixer, or uptake of
CO.sub.2 into the concrete has been achieved. The controller may
send output to additional actuators such as an actuator for
controlling water addition or an actuator controlling admixture
addition (not shown). An optional telemetry system 12 may be used
to transmit information regarding the batch to a central location
to be used, e.g., to store data for use in future batches and/or to
use for modification of the same or similar mixes in other
locations.
[0318] FIGS. 2 and 3 show a mobile cement mixer, in this case, a
ready mix truck. FIG. 2 shows a ready mix truck 1 with a detachable
carbon dioxide delivery system. Carbon dioxide is supplied from a
carbon dioxide supply 8 via a conduit that is attachable to a
conduit on the truck 2 at a junction 4. Controller 6 controls the
supply of carbon dioxide to the drum of the truck 2 via an actuator
5. Sensors, such as CO.sub.2 sensors may be located at leak areas
outside and/or inside the drum 2 and send signals regarding
atmospheric CO.sub.2 content to the controller 6. In addition, one
or more temperature sensors may sends signals regarding the
temperature of the concrete mix to the controller 6. Additional
sensors, such as moisture and rheology sensors, or additional
CO.sub.2 sensors in worker areas in the vicinity of the mixer may
be used (not shown) and send additional signals to the controller.
The controllers sends a signal to the actuator (e.g., valve) 5 to
control addition of carbon dioxide to the drum 2. Additional
actuators may be controlled by the controller, such as to control
addition of an admixture to the drum 2. An optional telemetry
system 7 may be used to transmit information regarding the batch to
a central location to be used, e.g., to store data for use in
future batches and/or to use for modification of the same or
similar mixes in other locations. FIG. 3 shows a ready mix truck
with attached carbon dioxide delivery system that travels with the
truck 1. This can be useful to, e.g., optimize exposure of the
cement mix to carbon dioxide. Carbon dioxide is supplied from a
carbon dioxide supply 7 via a conduit 3 that is attachable the
truck and delivers carbon dioxide to the drum of the truck 2.
Controller 5 controls the supply of carbon dioxide to the drum of
the truck 2 via an actuator 4. Sensors, such as CO.sub.2 sensors
may be located at leak areas outside and/or inside the drum 2 and
send signals regarding atmospheric CO.sub.2 content to the
controller 5. In addition, one or more temperature sensors may
sends signals regarding the temperature of the concrete mix to the
controller 5. Additional sensors, such as moisture and rheology
sensors, or additional CO.sub.2 sensors in worker areas in the
vicinity of the mixer may be used (not shown) and send additional
signals to the controller. The controllers sends a signal to the
actuator (e.g., valve) 4 to control addition of carbon dioxide to
the drum 2. Additional actuators may be controlled by the
controller, such as to control addition of an admixture to the drum
2. An optional telemetry system 6 may be used to transmit
information regarding the batch to a central location to be used,
e.g., to store data for use in future batches and/or to use for
modification of the same or similar mixes in other locations. In
certain embodiment the controller 5 is located remote from the
truck and receives the signals from the telemetry system, and
transmits signals which are received and acted upon by the actuator
4.
D. Mixers
[0319] The mixer in which the carbon dioxide is contacted with the
cement mix, e.g., hydraulic cement mix during mixing may be any
suitable mixer. The mixer may be relatively fixed in location or it
may provide both mixing and transport to a different location from
the mixing location.
[0320] In certain embodiments, the mixer is fixed or relatively
fixed in location. Thus, for example, in certain embodiments the
mixer is part of a pre-casting apparatus. For example, the mixer
may be configured for mixing concrete before introducing the
concrete into a mold to produce a precast concrete product. In
certain embodiments, the mixer is configured to mix concrete before
introducing the concrete into a mold, and the addition of carbon
dioxide to the concrete mix, the components of the concrete mix,
and, optionally, other ingredients such as one or more admixtures,
are adjusted so that a desired level of flow of the concrete mix,
generally very low or no flow, is combined with a desired level of
compactability so that the concrete may be compacted within a
certain range of parameters during and after delivery to a mold,
and so that the final product possesses a desired hardening time,
strength, shrinkage, and other characteristics as desired. For
example, a gas tube to deliver carbon dioxide into the mixer may be
placed with the gas line positioned in such a way that it does not
interfere with the normal mixer operation. Gas is delivered in
proportion to the amount of cement, for example in the range 0.5%
to 2.5%, or any other suitable range as described herein. The gas
delivery can be confined to the normal mixing time. In certain
embodiments gas delivery may be triggered by a gate for the cement
addition pipe. When the gate closes (signaling completion of cement
addition) a magnetic proximity sensor detects the closed state and
triggers the start of the carbon dioxide flow.
[0321] In certain embodiments in which the mixer is a fixed mixer,
for example in a dry cast or wet cast pre-casting operation, the
mixer is configured to mix concrete and to deliver it to a holding
component, e.g., a hopper, which further delivers the concrete to a
mold, optionally via a feedbox. Additional carbon dioxide can be
added to the cement mix, e.g., hydraulic cement mix at the hopper
and/or feedbox, if desired. See U.S. patent application Ser. No.
13/660,447 incorporated herein by reference in its entirety. In
certain embodiments, no further carbon dioxide is added to the mix
(apart from carbon dioxide in the atmosphere) after the concrete
exits the mixer.
[0322] The addition of carbon dioxide may affect the compactability
and thus the strength of the final object, e.g., precast object. In
the case of a wet cast operation, flowability is also a
consideration. Thus, in certain embodiments, the addition of carbon
dioxide to the concrete mix, the components of the concrete mix,
and, optionally, other ingredients such as one or more admixtures,
are adjusted so that a desired level of compactability (strength)
and/or flowability of the cement mix, e.g., hydraulic cement mix,
e.g., concrete, is achieved, generally a level of compactability
(strength) and/or flowability similar to the level that would be
present without the addition of the carbon dioxide, so that the
final product after the concrete is poured into the mold and
compacted at possesses a desired strength, such as a desired 1-,
7-, 28 and/or 56-day strength, and/or so that the flowability is at
a desired value. In the case of the pre-cast mixer, the addition of
carbon dioxide, components of the concrete mix, and/or additional
components such as one or more admixtures, may be adjusted so that
compactability and/or 1-, 7-, 28 and/or 56-day strength of the
final concrete mix is within 50, 40, 30, 20, 10, 8, 5, 4, 3, 2, 1,
0.5, or 0.1% of the value or values that would be achieved without
the addition of carbon dioxide, or is within 50, 40, 30, 20, 10, 8,
5, 4, 3, 2, 1, 0.5, or 0.1% of a predetermined desired value. In
certain embodiments, the addition of carbon dioxide, components of
the concrete mix, and/or additional components such as one or more
admixtures, may be adjusted so that compactability and/or 1-, 7-,
and/or 28-day strength of the final concrete mix of the final
concrete mix is within 10% of the compactability and/or 1-, 7-,
and/or 28-day strength of the final concrete mix that would be
achieved without the addition of carbon dioxide. In certain
embodiments, the addition of carbon dioxide, components of the
concrete mix, and/or additional components such as one or more
admixtures, may be adjusted so that compactability and/or 1-, 7-,
and/or 28-day strength of the final concrete mix is within 5% of
the compactability and/or 1-, 7-, and/or 28-day strength of the
final concrete mix that would be achieved without the addition of
carbon dioxide. In certain embodiments, the addition of carbon
dioxide, components of the concrete mix, and/or additional
components such as one or more admixtures, may be adjusted so that
compactability and/or 1-, 7-, and/or 28-day strength of the final
concrete mix is within 2% of the compactability and/or 1-, 7-,
and/or 28-day strength of the final concrete mix that would be
achieved without the addition of carbon dioxide. Other limits and
ranges of compactability and/or 1-, 7-, and/or 28-day strength of
the final concrete mix, as described herein, may also be used. Any
suitable measurement method for determining compactability and/or
1-, 7-, and/or 28-day strength of the final concrete mix may be
used. In certain embodiments, in addition to the desired
compactability and/or 1-, 7-, and/or 28-day strength of the final
concrete mix, one or more additional characteristics are achieved,
such as that shrinkage is within certain desired ranges, or above
or below certain threshold numbers, as determined by standard
methods in the art. In all cases, if the operation is a wet cast
operation, additionally, or alternatively, flowability may be
modulated, e.g., by use of one or more admixtures, for example so
that flowability is within 50, 40, 30, 20, 10, 8, 5, 4, 3, 2, 1,
0.5, or 0.1% of the value or values that would be achieved without
the addition of carbon dioxide, or within 50, 40, 30, 20, 10, 8, 5,
4, 3, 2, 1, 0.5, or 0.1% of a predetermined value. Any suitable
admixture, as described herein, may be used. In certain embodiments
the admixture comprises a set retarder. In certain embodiments, the
admixture comprises a carbohydrate, such as a saccharide, e.g., a
sugar or sugar derivative. In certain embodiments, the admixture is
selected from the group consisting of fructose, sodium
glucoheptonate, and sodium gluconate. In certain embodiments, the
admixture is sodium gluconate, e.g., sodium gluconate delivered to
achieve a percentage, per weight of cement, of 0.05-0.8%, 0.1-0.8%,
or 0.1-0.6%, or 0.1-0.5%, or 0.2-0.5%, or 0.2-3%, or 0.2-2%, or
0.2-1%. In certain embodiments a second admixture is also used,
such as any of the admixtures described herein.
[0323] In certain embodiments, the mixer is a transportable mixer.
"Transportable mixer," as that term is used herein, includes mixers
into which components of a cement mix, e.g., hydraulic cement mix
are placed in one location and the cement mix, e.g., hydraulic
cement mix is transported to another location which is remote from
the first location, then used. A transportable mixer is transported
by, for example, road or rail. As used herein, a transportable
mixer is not a mixer such as those used in a pre-cast concrete
operations. Thus, in certain embodiments, the mixer may be the drum
of a ready-mix truck in which a concrete mix is prepared for
delivery to a worksite. In this case, the mixer is configured to
mix concrete and to deliver it to a worksite, and the addition of
carbon dioxide to the concrete mix, the components of the concrete
mix, and, optionally, other ingredients such as one or more
admixtures, are adjusted so that a desired level of flow of the
cement mix, e.g., hydraulic cement mix, i.e., concrete, generally a
level of flow that is similar to the level that would be present
without the addition of the carbon dioxide, or a predetermined
flowability, is achieved, and so that the final product after
pouring at the worksite possesses a desired hardening time,
strength, shrinkage, and other characteristics as desired. In the
case of the ready-mix mixer, the addition of carbon dioxide,
components of the concrete mix, and/or additional components such
as one or more admixtures, may be adjusted so that flowability of
the final concrete mix is within 50, 40, 30, 20, 10, 8, 5, 4, 3, 2,
1, 0.5, or 0.1% of the flowability that would be achieved without
the addition of carbon dioxide, or a predetermined flowability. In
certain embodiments, the addition of carbon dioxide, components of
the concrete mix, and/or additional components such as one or more
admixtures, may be adjusted so that flowability of the final
concrete mix is within 10% of the flowability that would be
achieved without the addition of carbon dioxide, or a predetermined
flowability. In certain embodiments, the addition of carbon
dioxide, components of the concrete mix, and/or additional
components such as one or more admixtures, may be adjusted so that
flowability of the final concrete mix is within 5% of the
flowability that would be achieved without the addition of carbon
dioxide, or a predetermined flowability. In certain embodiments,
the addition of carbon dioxide, components of the concrete mix,
and/or additional components such as one or more admixtures, may be
adjusted so that flowability of the final concrete mix is within 2%
of the flowability that would be achieved without the addition of
carbon dioxide, or a predetermined flowability. Other limits and
ranges of flowability, as described herein, may also be used. Any
suitable measurement method for determining flowability may be
used, such as the well-known slump test. In certain embodiments, in
addition to the desired flowability, one or more additional
characteristics are achieved, such as that shrinkage and/or
strength, such as compressive strength, at one or more times after
pouring of the concrete are within certain desired ranges, or above
or below certain threshold numbers, as determined by standard
methods in the art. The addition of carbon dioxide, components of
the concrete mix, and/or additional components such as one or more
admixtures, may be adjusted so that 1-, 7-, 28, and/or 56-day
strength of the final concrete mix is within 50, 40, 30, 20, 10, 8,
5, 4, 3, 2, 1, 0.5, or 0.1% of the value or values that would be
achieved without the addition of carbon dioxide, or a predetermined
strength value.
[0324] It will be appreciated that, depending on the mix design,
dose of carbon dioxide, and/or other aspects of the mix or
conditions under which the concrete is mixed and/or used, the
carbonated concrete may have a greater compressive strength at one
or more time points compared to uncarbonated concrete; this is
especially likely when a low dose of carbon dioxide is used, such
as a dose of less than 1% bwc (see Low Dose section. In this case,
the addition of a particular dose of carbon dioxide may result in
an increase in strength, e.g., compressive strength, such as an
increase of at least 1, 2, 3, 4, 5, 7, 10, 15, 20, 30, 40, or 50%
compared to uncarbonated concrete of the same mix design and under
the same conditions at one or more times after mixing, such as at
24 hours, 3 days, 7 days, 28 days, 56 days, or the like;
alternatively, or additionally, the amount of cement in the mix may
be reduced so that the carbonated mix contains less cement than the
uncarbonated mix but reaches an acceptable compressive strength at
one or more desired times after mixing, such as within 20, 10, 5,
4, 3, 2, or 1% of the compressive strength of an uncarbonated mix
with the normal amount of cement. In certain embodiments, the
amount of cement in the mix may be reduced by at least 1, 2, 3, 4,
5, 6, 7, 8, 9, 10, 12, 15, 20, 25, or 30% compared to uncarbonated
mix and still achieve the desired strength at the desired time(s).
These considerations of increased strength and/or decreased use of
cement apply to both transportable and stationary operations. In
certain embodiments, the addition of carbon dioxide, components of
the concrete mix, and/or additional components such as one or more
admixtures, may be adjusted so that 1-, 7-, 28, and/or 56-day
strength of the final concrete mix of the final concrete mix is
within 10% of the 1-, 7-, 28 and/or 56-day strength of the final
concrete mix that would be achieved without the addition of carbon
dioxide, or a predetermined strength value. In certain embodiments,
the addition of carbon dioxide, components of the concrete mix,
and/or additional components such as one or more admixtures, may be
adjusted so that 1-, 7-, 28 and/or 56-day strength of the final
concrete mix is within 5% of the 1-, 7-, 28 and/or 56-day strength
of the final concrete mix that would be achieved without the
addition of carbon dioxide, or a predetermined strength value. In
certain embodiments, the addition of carbon dioxide, components of
the concrete mix, and/or additional components such as one or more
admixtures, may be adjusted so that 1-, 7-, 28 and/or 56-day
strength of the final concrete mix is within 2% of the 1-, 7-, 28
and/or 56-day strength of the final concrete mix that would be
achieved without the addition of carbon dioxide, or a predetermined
strength value. Other limits and ranges of 1-, 7-, 28 and/or 56-day
strength of the final concrete mix, as described herein, may also
be used. Any suitable measurement method for determining 1-, 7-, 28
and/or 56-day strength of the final concrete mix may be used. In
certain embodiments, in addition to the desired 1-, 7-, 28 and/or
56-day strength of the final concrete mix, one or more additional
characteristics are achieved, such as that shrinkage is within
certain desired ranges, or above or below certain threshold
numbers, as determined by standard methods in the art.
[0325] In embodiments in which an admixture is used, any suitable
admixture, as described herein, may be used. In certain embodiments
the admixture comprises a set retarder. In certain embodiments, the
admixture comprises a carbohydrate, such as a saccharide, e.g., a
sugar. In certain embodiments, the admixture is selected from the
group consisting of fructose, sodium glucoheptonate, and sodium
gluconate. In certain embodiments, the admixture is sodium
gluconate, e.g., sodium gluconate at a percentage of 0.01-2%, or
0.01-1%, or 0.01-0.8%, or 0.01-0.5%, or 0.01-0.1%, or 0.1-0.8%, or
0.1-0.6%, or 0.1-0.5%, or 0.2-0.5%, or 0.2-3%, or 0.2-2%, or
0.2-1%. In certain embodiments, the admixture is fructose, e.g.,
fructose at a percentage of 0.01-2%, or 0.01-1%, or 0.01-0.8%, or
0.01-0.5%, or 0.01-0.1%, or 0.1-0.8%, or 0.1-0.6%, or 0.1-0.5%, or
0.2-0.5%, or 0.2-3%, or 0.2-2%, or 0.2-1%. In certain embodiments a
second admixture is also used, such as any of the admixtures
described herein.
[0326] One type of transportable mixer is a volumetric truck. A
volumetric concrete truck is a truck that carries and mixes
concrete onsite by mixing aggregate, cement and water at the job
site, generally by using a belt to measure the ingredients and an
auger to mix the concrete before discharging. A schematic of a
truck can be seen in FIG. 147. As seen in FIG. 147, the concrete is
mixed in an auger and then discharged. This auger is in a trough
and is typically covered with a rubber mat. Thus, in this
embodiment, the mixer is the augur, and CO.sub.2 gas or gas/solid
can be added to the mixing concrete from the top of the auger
through a conduit. The rubber roof keeps the CO.sub.2 enclosed in
the trough and allows it to mix with the concrete before discharge.
The CO.sub.2 can be controlled by, e.g., using a flow meter and a
solenoid. The system can be controlled manually, using a knob on
the flow meter and manually opening the solenoid. It can also be
controlled automatically by, e.g., getting a signal from the truck
computer that corresponds to the rate at which cement is being
metered into the mixing hopper and be triggered when the auger is
moving. The source of carbon dioxide can be any source as described
herein, for example, a liquid tank or a gas tank. In the latter
case, a high pressure CO.sub.2 cylinder can be mounted on the truck
in order to supply the CO.sub.2 for the concrete. The cylinder may
also be heated (using a heating jacket) if the flow rate needed
exceeds that possible by the natural boiling inside the cylinder.
These trucks can do up to 60 m.sup.3/hr (1 m.sup.3/min), but
typically only carry enough material for .about.8 m.sup.3 of
concrete. This would mean a maximum CO.sub.2 flow rate between
60-500 SLPM depending on cement content of the mix and CO.sub.2
dose. Other aspects are as described above for transportable
mixers.
[0327] It will be appreciated that, both in the case of a wet cast
(such as readymix) or a dry cast, different mixes may require
different treatment in order to achieve a desired flowability
and/or compactability, and that mix types may be tested in advance
and proper treatment, e.g., proper type and/or percentage of
admixture determined. In certain cases admixture may not be
required; indeed, with certain mix types and carbon dioxide
concentrations, compactability (strength) or flowability may be
within acceptable limits; e.g., strength may even be improved in
certain mix types at certain levels of carbon dioxide addition.
Also, the point in the procedure in which ingredients are
introduced can affect one or more characteristics of the product,
as can be determined in routine testing and mix adjustment.
[0328] The mixer may be closed (i.e., completely or substantially
completely airtight) or open (e.g., the drum of a ready mix truck,
or a precast mixer with various leak points). The mixer may be one
of a plurality of mixers, in which different portions of a cement
mix, e.g., hydraulic cement mix are mixed, or it may be a single
mixer in which the entire cement mix, e.g., hydraulic cement mix,
such as a concrete mix, except in some cases additional water, is
mixed.
[0329] Methods of Carbon Dioxide Delivery
[0330] Any suitable mixer for mixing concrete in an operation to
produce concrete for use in objects, such as for use in producing
building materials, may be used. In some cases a mixer may be used
where the desired dose or uptake of carbon dioxide may be achieved
using gas delivery alone. For example, in most pre-cast mixers, the
mixer is enclosed but not gas-tight (i.e., not open to the
atmosphere, although not gas tight, such that leak points are
available for, e.g., carbon dioxide sensors) and the head space and
mixing times are such that a desired dose or uptake can be achieved
with nothing more than gaseous carbon dioxide delivery.
[0331] In some cases, however, such as in a ready mix truck where
head space is relative less than in a typical precast mixer,
additional efficiency may be desired, or necessary, in order to
achieve a desired carbon dioxide dose or uptake. In these cases,
the use of carbon dioxide-charged mix water, or liquid carbon
dioxide delivered so as to form a gas and a solid, or addition of
solid carbon dioxide, or any combination thereof, may be used. The
carbon dioxide may be delivered to the mixer as a liquid which,
through proper manipulation of delivery, such as flow rate and/or
orifice selection, becomes a mixture of gaseous carbon dioxide and
solid carbon dioxide upon delivery, for example, in an approximate
1:1 ratio. The gaseous carbon dioxide is immediately available for
uptake into the cement mix, e.g., hydraulic cement mix, while the
solid carbon dioxide effectively serves as a time-delayed delivery
of gaseous carbon dioxide as the solid gradually sublimates to gas.
Additionally, or alternatively, carbon dioxide-charged mix water
may be used. Carbon dioxide-charged water is routinely used in,
e.g., the soda industry, and any suitable method of charging the
mix water may be used. The water may be charged to achieve a carbon
dioxide concentration of at least 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10
g CO.sub.2/L water. Carbon dioxide-charged mix water can deliver a
significant portion of the desired carbon dioxide dose for a cement
mix, e.g., hydraulic cement mix, for example, at least 5, 10, 15,
20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95%
of the total carbon dioxide delivered to a batch of cement mix,
e.g., hydraulic cement mix may be delivered in the mix water. In
some cases, 100% of the carbon dioxide may be delivered in the mix
water. In some cases, at least 20% of the carbon dioxide is
delivered in the mix water. In some cases, at least 30% of the
carbon dioxide is delivered in the mix water. Without being bound
by theory, it is thought that the carbon dioxide thus delivered
reacts rapidly with components of the cement mix, e.g., hydraulic
cement mix, allowing further uptake of gaseous carbon dioxide by
the water. Carbon dioxide may also be delivered in solid form,
i.e., as dry ice, directly, as described elsewhere herein.
[0332] A ready mix operation is an example of a system where it may
be desirable to use one or both of carbon dioxide-charged water and
liquid carbon dioxide delivery. A ready mix truck drum is open to
the atmosphere and has a relatively small head space in comparison
to the mass of concrete, which is typically 6 to 10 cubic meters
when the truck is batched to capacity, which it is as often as
possible. Mixing time at the batching site may be relatively short.
Therefore the use of carbonated mix water and liquid CO.sub.2 may
be used to ensure that a desired dose of CO.sub.2 is delivered. For
example, in a ready mix operation in which a carbon dioxide
delivery of 1.5% is desired: The volume of gas to be added is
.about.2.66 m.sup.3 of gas/m.sup.3 of concrete (assuming 350
kg/m.sup.3 of cement being carbonated at 1.5%). Mix water is
typically represented by added water and excess moisture contained
in the aggregate. If the free mix water (.about.160 L/m.sup.3) is
carbonated with CO.sub.2 using existing carbonation technology,
such as that used in the soda industry, to 10 g of CO.sub.2/L of
water this represents approximately 1/3 of the target carbon
dioxide delivery of 1.5% bwc. Contact with cement results in rapid
carbonation of the dissolved CO.sub.2, and the water is quickly
ready for additional carbon dioxide dissolution once it is in the
truck and in contact with the cement. The use of carbon dioxide in
the mix water reduces the total carbon dioxide to be added to the
truck to 3.66 kg of CO.sub.2 (or about 1.85 m.sup.3 gas/m.sup.3
concrete). This amount may still be too high to be universally
delivered in atmospheric pressure gas form. Therefore liquid
CO.sub.2 injection into the truck can be used for the balance of
the carbon dioxide supply. Liquid CO.sub.2 injection of the
remaining 3.66 kg CO.sub.2/m.sup.3 in the truck can be done using a
controlled flow rate that is based upon sensors and a calibrated
CO.sub.2 uptake rate. See Control Mechanisms as described herein.
Upon delivery through a nozzle the liquid transforms into a mixture
of solid and gaseous carbon dioxide. The liquid delivery can
result, e.g., in 1.75 kg of solid CO.sub.2 snow (with a density of
1560 kg/m.sup.3) and 1.9 kg of CO.sub.2 gas (0.96 m.sup.3 gas). The
gas is immediately be available for uptake by the mix water while
the solid CO.sub.2 serves as a time delayed CO.sub.2 delivery, as
the solid gradually sublimates to gas. This process reduces the
gaseous volume injected into the truck to approximately 29% of the
volume needed if the entire CO.sub.2 delivery had been via gaseous
CO.sub.2. In some cases part of the concrete mix, e.g., the
aggregate, may also be wet. In that case, less mix water is used
and correspondingly more liquid carbon dioxide. Moisture sensors,
e.g., to sense the moisture content of the aggregate, may be used
to provide information to allow for the adjustment, even on a
batch-by-batch basis. This approach can allow for higher uptake
rates and greater efficiency.
[0333] Exemplary embodiments include a method for producing a
cement mix, e.g., hydraulic cement mix comprising (i) placing
components of the cement mix, e.g., hydraulic cement mix in a mixer
and mixing the components; and (ii) delivering liquid CO.sub.2 via
an opening in a conduit into the mixer in such a manner as to cause
the liquid CO.sub.2 to form a mixture of gaseous and solid CO.sub.2
which then contact the cement mix, e.g., hydraulic cement mix. The
delivery of the liquid may be controlled in such a manner, e.g., by
adjusting flow rate and/or orifice, or other adjustable feature or
measure, as to form a mixture of gaseous to solid carbon dioxide in
a ratio in the range of 1:10 to 10:1, or 1:5 to 5:1, or 1:3 to 3:1,
or 1:2 to 2:1, or 1:1.5 to 1.5:1, or 1:1.2 to 1.2 to 1. The cement
mix, e.g., hydraulic cement mix comprises water and the water may
be charged with CO.sub.2 before delivery to the mixer as described
herein, for example to a level of at least 2 g CO.sub.2/L water, or
at least 4 g CO.sub.2/L water, or at least 6 g CO.sub.2/L water, or
at least 8 g CO.sub.2/L water, or at least 9 g CO.sub.2/L water, or
at least 10 g CO.sub.2/L water. The mixer may be any suitable
mixer, such as a stationery mixer or a transportable mixer, e.g.,
the drum of a ready mix concrete truck. When the mixer is the drum
of a ready mix concrete truck, the liquid CO.sub.2 may be supplied
to the mixer at a batching plant, or it may be supplied to the
mixer during transport of the batch to a job site, or even at the
job site itself, or a combination thereof. The method may further
include monitoring a characteristic of the cement mix, e.g.,
hydraulic cement mix, a gas mixture in contact with the cement mix,
e.g., hydraulic cement mix, a component of a cement mix, e.g.,
hydraulic cement mix apparatus, or a component exposed to the
cement mix, e.g., hydraulic cement mix, and modulating the flow of
liquid CO.sub.2 according to the characteristic monitored. For
example, CO.sub.2 concentration, temperature, moisture content,
rheology, pH, or a combination thereof may be monitored, as
detailed elsewhere herein. When CO.sub.2 is monitored, it may be
monitored in a portion of gas outside the mixer, e.g. at a leak
point or spill point.
[0334] Exemplary embodiments also include a method for producing a
cement mix, e.g., hydraulic cement mix comprising (i) contacting
components of the cement mix, e.g., hydraulic cement mix with
CO.sub.2-charged water, wherein the water is charged with CO.sub.2
to a level of at least 2 g/L, 3 g/L, 4 g/L, 6 g/L, 8 g/L, 9 g/L, or
10 g/L, and mixing the components and the water. Embodiments
further include a method of producing a carbonated cement mix,
e.g., hydraulic cement mix comprising (i) determining a dose of
CO.sub.2 to be delivered to the cement mix, e.g., hydraulic cement
mix; and (ii) delivering at least 10, 20, 30, 40, 50, 60, 70, 80,
90, or 100% of the dose of CO.sub.2 as CO.sub.2 dissolved in mix
water for the cement mix, e.g., hydraulic cement mix. In certain
embodiments the dose is 0.1-10%, or 0.5-5%, or 0.5-4%, or 0.5-3%,
or 0.5-2%, or 1-5%, or 1-4%, or 1-3%, or 1-2% CO.sub.2 bwc. In
certain embodiments the dose is 1.5% CO.sub.2 bwc. Delivery of
carbon dioxide-charged mix water as described may be combined in
some embodiments with delivery of gaseous and/or liquid carbon
dioxide. Further embodiments in which carbonated mix water is used
are described elsewhere herein.
[0335] Exemplary embodiments further include an apparatus for
carbonating a cement mix, e.g., hydraulic cement mix comprising (i)
a mixer for mixing the cement mix, e.g., hydraulic cement mix; (ii)
a source of liquid CO.sub.2; and (iii) a conduit operably
connecting the source of liquid CO.sub.2 to the mixer, wherein the
conduit comprises an orifice through which the liquid CO.sub.2
exits the conduit into the mixer. The conduit can include a system
for regulating the flow of the liquid CO.sub.2 where the system,
the orifice, or both, are configured to deliver the liquid CO.sub.2
as a combination of solid and gaseous CO.sub.2, such as by
regulating flow rate of the liquid CO.sub.2 and/or orifice
configuration, such as to produce a ratio of solid to gaseous
CO.sub.2 in the range of 1:10 to 10:1, or 1:5 to 5:1, or 1:3 to
3:1, or 1:2 to 2:1, or 1:1.5 to 1.5:1, or 1:1.2 to 1.2 to 1, for
example, between 1:3 and 3:1, or between 1:2 and 2:1. The mixer can
be a transportable mixer, such as a drum of a ready-mix truck. The
source of liquid CO.sub.2 and the conduit may remain at a batching
facility after the transportable is charged, or may accompany the
transportable mixer when the transportable mixer transports the
cement mix, e.g., hydraulic cement mix. The apparatus may further
include a system for delivering CO.sub.2-charged water to the mixer
comprising a source of CO.sub.2-charged water and a conduit
operably connected to the source and configured to deliver the
water to the mixer, which may in some cases further include a
charger for charging the water with CO.sub.2. In certain cases the
mixer is transportable and the system for delivering
CO.sub.2-charged water to the mixer is detachable from the mixer
during transport, e.g., if the mixer is the drum of a ready mix
truck the system for delivering and, optionally, charging
CO.sub.2-charged water remains at the batching facility.
[0336] Exemplary embodiments also include an apparatus for
producing a carbonated cement mix, e.g., hydraulic cement mix
comprising (i) a mixer for mixing the cement mix, e.g., hydraulic
cement mix; and (ii) at least two of (a) a source of gaseous
CO.sub.2 operably connected to the mixer and configured to deliver
gaseous CO.sub.2 to the mixer; (b) a source of liquid CO.sub.2
operably connected to the mixer and configured to deliver liquid
CO.sub.2 to the mixer and release the liquid CO.sub.2 into the
mixer as a mixture of gaseous and solid CO.sub.2; and (c) a source
of carbonated water operably connected to the mixer and configured
to deliver carbonated water to the mixer.
E. Retrofitting Existing Apparatus
[0337] In certain embodiments, the methods of the invention include
methods and apparatus for retrofitting an existing cement mix,
e.g., hydraulic cement mix apparatus to allow for the contact of
the mixing cement mix, e.g., hydraulic cement mix with carbon
dioxide. As used herein, the term "retrofit" is used in its
generally accepted sense to mean installing new or modified parts
or equipment into something previously manufactured or constructed.
The retrofit may modify the existing apparatus to perform a
function for which it was not originally intended or manufactured.
In the case of the present invention, a cement mix, e.g., hydraulic
cement mix apparatus to be retrofitted is not originally
constructed to allow addition of carbon dioxide to a cement mix,
e.g., hydraulic cement mix during mixing of the cement mix, e.g.,
hydraulic cement mix. Preferably, the retrofitting requires little
or no modification of the existing apparatus. The retrofitting may
include delivering to a site where a pre-existing cement mix, e.g.,
hydraulic cement mix apparatus is located the components necessary
to modify the existing cement mix, e.g., hydraulic cement mix
apparatus to allow exposure of a cement mix, e.g., hydraulic cement
mix to carbon dioxide during mixture. Instructions for one or more
procedures in the retrofitting may also be transported or
transmitted to the site of the existing cement mix, e.g., hydraulic
cement mix apparatus.
[0338] The retrofitting may include installing components necessary
to modify the existing cement mix, e.g., hydraulic cement mix
apparatus to allow exposure of a cement mix, e.g., hydraulic cement
mix to carbon dioxide during mixing. The components may include a
conduit for delivery of carbon dioxide to a cement mix, e.g.,
hydraulic cement mix mixer. The components may further include a
source of carbon dioxide. In systems in which a control system is
included, the retrofit may include modifying the existing control
system of the cement mix, e.g., hydraulic cement mix apparatus to
perform functions appropriate to the controlled addition of carbon
dioxide to the cement mix, e.g., hydraulic cement mix. Instructions
for such modifications may also be transmitted or sent to the site
of the existing cement mix, e.g., hydraulic cement mix apparatus
controller. Such modifications can include, for example, modifying
the existing controller settings to include timing the opening and
closing of a gas supply valve to deliver a flow of carbon dioxide
at a predetermined flow rate for a predetermined time from the
carbon dioxide source via the conduit to the mixer at a certain
stage in the hydraulic mix apparatus operations. They may also
include modifying the controller to modify the timing and/or amount
of water addition to the cement mix, e.g., hydraulic cement mix,
addition of admixture, and any other suitable parameter.
Alternatively, or in addition to, modifying the existing
controller, the retrofitting may include providing one or more new
controllers to the pre-existing cement mix, e.g., hydraulic cement
mix apparatus. The retrofitting can include transporting the new
controller or controllers to the site of the existing cement mix,
e.g., hydraulic cement mix apparatus. In addition, one or more
sensors, such as sensors for sensing the positions and/or states of
one or more components of the existing cement mix, e.g., hydraulic
cement mix apparatus, which were not part of the original
manufactured equipment, may be installed. The retrofit may include
transporting one or more sensors to the site of the existing cement
mix, e.g., hydraulic cement mix apparatus. Actuators, which may be
actuators in the retrofitted apparatus, e.g., a gas supply valve,
or in the original equipment, e.g., to move or start or stop
various operations such as addition of water, may be operably
connected to the retrofitted controller in order to modify the
operations of the cement mix, e.g., hydraulic cement mix apparatus
according to the requirements of contacting the cement mix, e.g.,
hydraulic cement mix with carbon dioxide. The retrofit may include
transporting one or more sensors to the site of the existing cement
mix, e.g., hydraulic cement mix apparatus.
III. Methods
[0339] In certain embodiments, the invention provides methods for
producing a carbonated cement mix in a mix operation in a cement
mix apparatus comprising (i) contacting a cement mix comprising
cement binder and aggregate in a mixer with carbon dioxide while
the cement mix is mixing; (ii) monitoring a characteristic of the
cement binder, the cement mix, a gas mixture in contact with the
cement mix or the mixer, or a component of the cement mix
apparatus; and (iii) modulating the exposure of the cement mix to
the carbon dioxide or another characteristic of the cement mix
operation, or a combination thereof according to the characteristic
monitored in step (ii). In some cases, only exposure of the cement
mix to the carbon dioxide is modulated; in other cases, only
another characteristic of the cement mix operation is modulated;
and in other cases, both are modulated.
[0340] The cement binder may be any suitable cement binder as
described herein, i.e., a cement binder containing calcium species
capable of reacting with carbon dioxide to form stable or
metastable reaction products, such as carbonates. The cement binder
may be a hydraulic cement, for example, a Portland cement. "Cement
mix," as that term is used herein, includes a mix of a cement
binder, e.g., a hydraulic cement, such as a Portland cement, with
aggregate; "concrete" is generally synonymous with "cement mix" as
those terms are used herein.
[0341] The mix operation may be any operation in which a cement
mix/concrete is produced for any of the various uses of such a mix.
Thus, the cement mix operation may be an operation in a mixer at a
precast facility for producing a cement mix for use in a dry cast
or wet cast operation. In other embodiments, the cement mix
operation may be an operation in a mixer for a ready mix operation,
e.g., the drum of a ready mix truck. Any other suitable cement mix
operation may also be used, so long as it is amenable to addition
of carbon dioxide to the cement mix during mixing, for example, a
mixer on site at a construction site. Thus, additional examples
include pug mill or twin shaft continuous mixers that can be used
for roller compacted concrete (dry mix) or CTB (cement treated
base) for road stabilization, which are continuous mix applications
rather than batch. While some of the aspects of water proportioning
might not be achievable there still exists the possibility to add
CO.sub.2 during the mixing step.
[0342] The characteristic monitored may be any suitable
characteristic that provides useful feedback to inform modulation
of exposure of the cement mix to carbon dioxide or another
characteristic of the cement mix operation. In certain embodiments,
the characteristic monitored is (a) mass of cement binder added to
the cement mix, (b) location of the cement binder in the mix
apparatus (e.g., coordinating carbon dioxide delivery with delivery
of cement binder; may be achieved by sensing the location of the
cement mix or by timing of the mix sequence, which can be input to
the controller), (c) carbon dioxide content of a gas mixture within
the mixer in contact with the cement mix, (d) carbon dioxide
content of a gas mixture exiting from the mixer, (e) carbon dioxide
content of gas mixture in the vicinity of the mix apparatus, (f)
temperature of the cement mix or a component of the mix apparatus
in contact with the cement mix, (g) rheology of the cement mix, (h)
moisture content of the cement mix, or (i) pH of the cement mix.
The location of water in the mix apparatus also be monitored, e.g.,
to determine when water addition is complete. These characteristics
and methods and apparatus for monitoring them are as described
elsewhere herein. When the mass of the cement binder is monitored,
the total amount of carbon dioxide to be added to the cement mix
may be modulated to accord with a predetermined desired exposure,
e.g., if a 1.5% carbon dioxide/cement exposure is desired, the
exact mass used in a particular batch may be used to determine the
exact total carbon dioxide to be added to the batch (which may be
used as is, or modified in response to other characteristics that
are monitored). When location of the cement binder or water in the
mix apparatus is monitored, the modulation of carbon dioxide flow
may be a simple on/off, e.g., when the cement mix and/or water is
determined to have entered the mixer, carbon dioxide flow may be
turned on at that time or at a predetermined time after that time.
In certain embodiments, the characteristic monitored in step (ii)
comprises carbon dioxide content of a gas mixture exiting from the
mixer, e.g., at a leak point of the mixer. In this embodiment,
and/or in other embodiments in which a carbon dioxide content of a
gas mixture is monitored, the exposure of the cement mix to carbon
dioxide can be modulated when the carbon dioxide content of the gas
mixture reaches a threshold value, and/or when the rate of change
of the carbon dioxide content of the gas mixture reaches a
threshold value. The modulation can be an increase in the rate of
carbon dioxide addition to the cement mix, a decrease, or even a
full stop. In certain embodiments, the characteristic monitored is
the temperature of the cement mix or a component of the mix
apparatus in contact with the cement mix. For example, a wall of
the mixer may be monitored for temperature. The exposure of the
cement mix to carbon dioxide can be modulated when the temperature
of the cement mix or a component of the mix apparatus in contact
with the cement mix, or a combination of a plurality of such
temperatures, reaches a threshold value and/or when the rate of
change of the temperature of the cement mix or a component of the
mix apparatus in contact with the cement mix reaches a threshold
value. If temperature is used as a measure for the threshold value,
it may be an absolute temperature, or it may be a temperature
relative to the temperature of the mix before the addition of
carbon dioxide, e.g., a temperature that is a certain number of
degrees above the starting temperature, for example 10-50.degree.
C. above the starting value, or 10-40.degree. C. above the starting
value, or 10-30.degree. C. above the starting value. The exact
difference between starting and threshold temperature may be
predetermined for a particular mix recipe by determining the
relationship between carbonation and temperature for that recipe,
or for that particular cement binder in relation to other
components of that recipe.
[0343] In certain embodiments, a plurality of characteristics of
the cement binder, the cement mix, a gas mixture in contact with
the cement mix or the mixer, or a component of the cement mix
apparatus are monitored, e.g., at least 2, 3, 4, 5, 6, 7, 8, 9, or
10 characteristics, for example, at least 2 characteristics. In
certain embodiments, at least 2 of (a) mass of cement binder added
to the cement mix, (b) location of the cement binder in the mix
apparatus, (c) carbon dioxide content of a gas mixture within the
mixer in contact with the cement mix, (d) carbon dioxide content of
a gas mixture exiting from the mixer, (e) carbon dioxide content of
gas mixture in the vicinity of the mix apparatus, (f) temperature
of the cement mix or a component of the mix apparatus in contact
with the cement mix, (g) rheology of the cement mix, (h) moisture
content of the cement mix, or (i) pH of the cement mix are
monitored. In certain embodiments, at least 3 of (a) mass of cement
binder added to the cement mix, (b) location of the cement binder
in the mix apparatus, (c) carbon dioxide content of a gas mixture
within the mixer in contact with the cement mix, (d) carbon dioxide
content of a gas mixture exiting from the mixer, (e) carbon dioxide
content of gas mixture in the vicinity of the mix apparatus, (f)
temperature of the cement mix or a component of the mix apparatus
in contact with the cement mix, (g) rheology of the cement mix, (h)
moisture content of the cement mix, or (i) pH of the cement mix are
monitored. In certain embodiments, at least 4 of (a) mass of cement
binder added to the cement mix, (b) location of the cement binder
in the mix apparatus, (c) carbon dioxide content of a gas mixture
within the mixer in contact with the cement mix, (d) carbon dioxide
content of a gas mixture exiting from the mixer, (e) carbon dioxide
content of gas mixture in the vicinity of the mix apparatus, (f)
temperature of the cement mix or a component of the mix apparatus
in contact with the cement mix, (g) rheology of the cement mix, (h)
moisture content of the cement mix, or (i) pH of the cement mix are
monitored. In certain embodiments, at least 5 of (a) mass of cement
binder added to the cement mix, (b) location of the cement binder
in the mix apparatus, (c) carbon dioxide content of a gas mixture
within the mixer in contact with the cement mix, (d) carbon dioxide
content of a gas mixture exiting from the mixer, (e) carbon dioxide
content of gas mixture in the vicinity of the mix apparatus, (f)
temperature of the cement mix or a component of the mix apparatus
in contact with the cement mix, (g) rheology of the cement mix, (h)
moisture content of the cement mix, or (i) pH of the cement mix are
monitored. In certain embodiments, at least 6 of (a) mass of cement
binder added to the cement mix, (b) location of the cement binder
in the mix apparatus, (c) carbon dioxide content of a gas mixture
within the mixer in contact with the cement mix, (d) carbon dioxide
content of a gas mixture exiting from the mixer, (e) carbon dioxide
content of gas mixture in the vicinity of the mix apparatus, (f)
temperature of the cement mix or a component of the mix apparatus
in contact with the cement mix, (g) rheology of the cement mix, (h)
moisture content of the cement mix, or (i) pH of the cement mix are
monitored.
[0344] In certain embodiments, the method alternatively, or
additionally, include monitoring the time of exposure of the cement
mix to the carbon dioxide, the flow rate of the carbon dioxide, or
both.
[0345] When an additional characteristic of the mix operation is
modulated in response to the monitoring, it may be any suitable
characteristic. In certain embodiments, the additional
characteristic includes (a) whether or not an admixture is added to
the cement mix, (b) type of admixture added to the cement mix, (c)
timing of addition of admixture to the cement mix, (d) amount of
admixture added to the cement mix, (e) amount of water added to the
cement mix, (f) timing of addition of water to the cement mix, (g)
cooling of the cement mix during or after carbon dioxide addition,
or a combination thereof. If an admixture is used, it may be any
suitable admixture for adjusting a characteristic of the cement
mix, e.g., an admixture to adjust the rheology (flowability) of the
mix, for example, in a wet cast operation. Examples of suitable
admixtures are described herein, e.g., carbohydrates or
carbohydrate derivatives, such as sodium gluconate.
[0346] The characteristic may be monitored, such as by one or more
sensors. Such sensors may transmit information regarding the
characteristic to a controller which processes the information and
determines if a modulation of carbon dioxide exposure or another
characteristic of the mix operation is required and, if so,
transmits a signal to one or more actuators to carry out the
modulation of carbon dioxide exposure or other characteristic of
the mix operation. The controller may be at the site of the mix
operation or it may be remote. Such sensors, controllers, and
actuators are described further elsewhere herein. If a controller
is used, it may store and process the information obtained
regarding the characteristic monitored in step (ii) for a first
batch of cement mix and adjust conditions for a subsequent second
cement mix batch based on the processing. For example, the
controller may adjust the second mix recipe, e.g., amount of water
used or timing of water addition, or carbon dioxide exposure in the
second batch to improve carbon dioxide uptake, or to improve
rheology or other characteristics of the mix, e.g., by addition
and/or amount of an admixture, and/or timing of addition of the
admixture. In such embodiments in which one or more conditions of a
second mix operation are adjusted, in certain embodiments the one
or more conditions of the second mix operation includes (a) total
amount of carbon dioxide added to the cement mix, (b) rate of
addition of carbon dioxide, (c) time of addition of carbon dioxide
to the cement mix, (d) whether or not an admixture is added to the
cement mix, (e) type of admixture added to the cement mix, (f)
timing of addition of admixture to the cement mix, (g) amount of
admixture added to the cement mix, (h) amount of water added to the
cement mix, (i) timing of addition of water to the cement mix, (j)
cooling the cement mix during or after carbon dioxide addition, or
a combination thereof. The controller can also receive additional
information regarding one or more characteristics of the cement mix
measured after the cement mix leaves the mixer, and adjusts
conditions for the second cement mix batch based on processing that
further comprises the additional information. In certain
embodiments, the one or more characteristics of the cement mix
measured after the cement mix leaves the mixer comprises (a)
rheology of the cement mix at one or more time points, (b) strength
of the cement mix at one or more time points, (c) shrinkage of the
cement mix, (d) water absorption of the cement mix, or a
combination thereof. Other characteristics include elastic modulus,
density, and permeability. Any other suitable characteristic may be
measured. The characteristic monitored can depend on the
requirements for a particular mix batch, although other
characteristics may also be monitored to provide data to the
controller for future batches in which those characteristics would
be required.
[0347] In embodiments in which a controller adjusts conditions for
a second mix operation based on input from a first mix operation,
the second mix operation may be in the same mix facility or it may
be in a different mix facility. In certain embodiments, the
controller, one or more sensors, one or more actuators, or
combination thereof, transmits information regarding the
characteristics monitored and conditions modulated to a central
controller that receives information from a plurality of
controllers, sensors, actuators, or combination thereof, each of
which transmits information from a separate mixer to the central
controller. Thus, for example, a first mix facility may have a
first sensor to monitor a first characteristic of the first mix
operation, and a second mix facility may have a second sensor to
monitor a second characteristic of a second mix operation, and both
may send information regarding the first and second characteristics
to a central controller, which processes the information and
transmit a signal to the first, second, or even a third mix
operation to adjust conditions based on the first and second
signals from the first and second sensors. Additional information
that will be typically transmitted to the central controller
includes mix components for the mixes at the first and second mix
operations (e.g., type and amount of cement binder, amount of water
and w/c ratio, types and amounts of aggregate, whether aggregate
was wet or dry, admixtures, and the like) amount, rate, and timing
of carbon dioxide addition, and any other characteristic of the
first and second mix operations that would be useful for
determining conditions to modulate future mix operations based on
the characteristics achieved in past mix operations. Any number of
mix operations may input information to the central controller,
e.g., at least 2, 3, 4, 5, 6, 7, 8, 9, or 10 mix operations, or at
least 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, or 100 mix
operations. The central controller may also receive any other
information that may be suitable to informing decisions regarding
mix operations to optimize one or more conditions of the mix
operation and/or of the cement mix produced in the operation. For
example, the central controller may receive information from
experiments conducted with various types of cements (e.g., various
types of Portland cements) carbonated under various conditions,
and/or exposed to various admixtures, such as at different times,
or in different concentrations, and the like, and the resulting
characteristics of the cement mix, such as rheology at one or more
time points, strength at one or more time points, and the like. Any
other suitable information, such as information published in
literature, or obtained in any manner, may be input into the
central controller. The information the central controller receives
can be processed and used to adjust cement mix operations at any
mix operation to which the central controller can transmit outputs.
Thus, the central controller can learn from numerous mix operations
to optimize future operations and, over time, can accumulate a
database to inform decisions in mix operations at a mix site even
if a particular mix recipe and/or conditions have never been used
at that site. The central controller can match to past mix recipes,
or predict optimum conditions for a new mix recipe based on
suitable algorithms using information in its database, or both.
[0348] In certain embodiments, the invention provides a method of
carbonating a cement mix in a mixer that is not completely airtight
in such a way as to achieve an efficiency of carbonation of at
least 60, 70, 80, 90, 95, 96, 97, 98, or 99%, wherein efficiency of
carbonation is the amount of carbon dioxide retained in the cement
mix per the total amount of carbon dioxide to which the cement mix
is exposed during mixing. The mixer may have leak points and other
aspects that make it less than airtight, such as seen in a typical
mixer for a precast operation. The mixer may be, e.g., the drum of
a ready mix truck which has a large opening to the outside
atmosphere. Such efficiency may be achieved, e.g., by using any of
the methods to modulate the exposure of the cement mix to carbon
dioxide as detailed above.
[0349] In certain embodiments, the invention provides a method for
producing a cement mix, e.g., hydraulic cement mix comprising (i)
contacting a cement mix, e.g., hydraulic cement mix comprising a
first portion of water and hydraulic cement in a mixer with carbon
dioxide while the cement mix, e.g., hydraulic cement mix is mixing;
and (ii) adding a second portion of water to the cement mix, e.g.,
hydraulic cement mix. In some aspects of this embodiment, the
contacting comprises directing a flow of carbon dioxide to the
cement mix, e.g., hydraulic cement mix. The second portion of water
may be added to the cement mix, e.g., hydraulic cement mix during
said flow or after said flow has ceased, for example, after said
flow has ceased. The method may include adding aggregate to the
cement mix, e.g., hydraulic cement mix to produce a concrete mix;
in certain embodiments, the aggregate comprises some or all of the
first portion of water. The aggregate may be added before the
contacting with the carbon dioxide. In certain embodiments, the
method includes (iii) adding an admixture to the cement mix, e.g.,
hydraulic cement mix, such as an admixture that modulates the
flowability of the cement mix, e.g., hydraulic cement mix. In
embodiments in which an admixture to modulate flowability is added,
the admixture may added in an amount to achieve a flowability in a
predetermined range of flowabilities, such as a predetermined range
of flowabilities that is determined by allowing for a margin from
the flowability of the cement mix, e.g., hydraulic cement mixture
without the addition of carbon dioxide. The admixture may be
selected from the group consisting of a polycarboxylate
superplasticer, a naphthalene HRWR, or any combination thereof. In
certain embodiments, the admixture contains sodium gluconate,
sucrose, glucose, molasses, corn syrup, EDTA, or a combination
thereof. In certain embodiments, the admixture contains sodium
gluconate. In certain embodiments, the admixture contains sucrose.
In certain embodiments, the admixture contains glucose. In certain
embodiments, the admixture contains molasses. In certain
embodiments, the admixture contains corn syrup. In certain
embodiments, the admixture contains EDTA. In certain embodiments,
the cement mix, e.g., hydraulic cement mix comprises Portland
cement. Whether or not the cement mix, e.g., hydraulic cement mix
comprises Portland cement, in certain embodiments cement mix, e.g.,
hydraulic cement mix comprising the first portion of water
comprises an amount of water so that the ratio of water to cement
(w/c ratio) is equal to or less than 0.5. In certain of these
embodiments, the first portion of water comprises an amount of
water so that the w/c ratio is in the range 0.1 to 0.5. the carbon
dioxide to which the cement mix, e.g., hydraulic cement mix is
exposed may be at least 50% pure. The cement mix, e.g., hydraulic
cement mix may be contacted with carbon dioxide by flowing carbon
dioxide over the surface of the mixing cement mix, e.g., hydraulic
cement mix. The flow of carbon dioxide directed to the cement mix,
e.g., hydraulic cement mix, e.g., the surface of the mix, may last
for 5 minutes or less, for example, the flow of carbon dioxide
directed to the cement mix, e.g., hydraulic cement mix may last for
0.5-5 minutes. In certain embodiments, in which solid carbon
dioxide is introduced into the cement mix, the solid carbon dioxide
sublimates to gaseous carbon dioxide and the delivery may be
extended to more than 20, 30, 40, 50, or 60 minutes. The method may
further comprise monitoring a characteristic of the cement mix,
e.g., hydraulic cement mix, a gas mixture in contact with the
cement mix, e.g., hydraulic cement mix, a component of a cement
mix, e.g., hydraulic cement mix apparatus, or a component exposed
to the cement mix, e.g., hydraulic cement mix, and modulating the
flow of carbon dioxide according to the characteristic monitored.
For example, the method may further comprise monitoring a carbon
dioxide concentration in a portion of gas adjacent to the cement
mix, e.g., hydraulic cement mix, such as in a portion of gas in the
mixer, or in a portion of gas outside the mixer, or both. The
carbon dioxide concentration may be monitored by a sensor. The
sensor may transmit a signal to a controller. The controller may
process the signal and transmits a signal to an actuator according
to the results of the processing, such as a controllable valve for
controlling the flow of carbon dioxide to contact the cement mix,
e.g., hydraulic cement mix. In addition to, or instead of carbon
dioxide, a temperature of the cement mix, e.g., hydraulic cement
mix, the mixer, or of another component exposed to the cement mix,
e.g., hydraulic cement mix may be monitored, for example, the
temperature of the mixer may be monitored, or the temperature of
the cement mix, e.g., hydraulic cement mix inside the mixer may be
monitored, or the temperature of a portion of the cement mix, e.g.,
hydraulic cement mix that is transported outside the mixer may be
monitored. The contacting of the cement mix, e.g., hydraulic cement
mix with carbon dioxide may be modulated according to the
temperature monitored, for example, when the temperature being
monitored, or a combination of temperatures being monitored,
exceeds a threshold value. The threshold value may be a value
determined relative to the initial temperature of the cement mix,
e.g., hydraulic cement mix before addition of carbon dioxide, such
as a threshold temperature or range of temperatures relative to the
initial temperature as described herein. Alternatively, the
threshold value may be an absolute value. The temperature may be
monitored by a sensor. The sensor may transmit a signal to a
controller. The controller may process the signal and transmit a
signal to an actuator according to the results of the processing.
The actuator may comprise a controllable valve for controlling the
flow of carbon dioxide to contact the cement mix, e.g., hydraulic
cement mix. The method of contacting the hydraulic cement with
carbon dioxide may include, in any of these embodiments,
controlling the contacting of the cement mix, e.g., hydraulic
cement mix with the carbon dioxide is controlled to achieve a
desired level of carbonation, such as a level as described herein,
for example, at least 0.5, 1, 2, 3, or 4%. In certain embodiments,
the exposure of the cement mix to carbon dioxide is modulated so as
to provide an efficiency of carbon dioxide uptake of at least 60,
70, 80, 90, 95, 96, 97, 98, or 99%, for example, at least 70%.
[0350] In certain embodiments, the invention provides a method for
producing a cement mix, e.g., hydraulic cement mix comprising (i)
contacting a cement mix, e.g., hydraulic cement mix comprising
water and hydraulic cement in a mixer with carbon dioxide while the
cement mix, e.g., hydraulic cement mix is mixing, wherein the
carbon dioxide is contacted with the surface of the cement mix,
e.g., hydraulic cement mix by directing a flow of carbon dioxide to
the surface of the mix from outside the mix, and wherein the flow
lasts less than 5 min. In certain embodiments, the cement mix,
e.g., hydraulic cement mix comprises aggregate. The cement mix,
e.g., hydraulic cement mix may further comprise an admixture. In
certain embodiments, the mixer is a transportable mixer, such as a
drum of a ready-mix truck. In certain embodiments, the mixer is a
mixer for pre-cast concrete. The method may further comprise
controlling the flow of the carbon dioxide according to feedback
from one or more sensors that monitor a characteristic selected
from the group consisting of a characteristic of the cement mix,
e.g., hydraulic cement mix, a gas mixture in contact with the
cement mix, e.g., hydraulic cement mix, a component of a cement
mix, e.g., hydraulic cement mix apparatus, or a component exposed
to the cement mix, e.g., hydraulic cement mix.
[0351] In certain embodiments, the invention provides a method for
producing a hydraulic cement mix comprising (i) contacting a cement
mix, e.g., hydraulic cement mix comprising water and hydraulic
cement in a mixer with carbon dioxide while the cement mix, e.g.,
hydraulic cement mix is mixing, wherein the carbon dioxide is
contacted with the surface of the cement mix, e.g., hydraulic
cement mix by directing a flow of carbon dioxide to the surface of
the mix from outside the mix, and wherein the carbon dioxide is a
component of a gaseous mixture that comprises at least 10, 20, 30,
40, 50, 60, 70, 80, 90, 95, or 99% carbon dioxide, such as at least
50% carbon dioxide. In certain embodiments, the hydraulic cement
comprises aggregate. In certain embodiments, the hydraulic cement
comprises an admixture. In certain embodiments, the mixer is a
transportable mixer, such as a drum of a ready-mix truck. In
certain embodiments, the mixer is a mixer for pre-cast
concrete.
[0352] In certain embodiments, the invention provides a method for
producing a cement mix, e.g., hydraulic cement mix comprising (i)
contacting a cement mix, e.g., hydraulic cement mix in a mixer with
carbon dioxide while the cement mix, e.g., hydraulic cement mix is
mixing; and (ii) adding an admixture to the cement mix, e.g.,
hydraulic cement mix. The contacting may be achieved by directing a
flow of carbon dioxide to the cement mix, e.g., hydraulic cement
mix. In certain embodiments, the admixture is an admixture that
modulates the flowability of the cement mix, e.g., hydraulic cement
mix. In certain of these embodiments, the admixture may be added in
an amount to achieve a flowability in a predetermined range of
flowabilities, such as a predetermined range of flowabilities
determined by allowing for a margin from the flowability of the
cement mix, e.g., hydraulic cement mixture without the addition of
carbon dioxide, for example, as described elsewhere herein. In
certain aspects of the fourth embodiment, the admixture is selected
from the group consisting of a polycarboxylate superplasticer, a
naphthalene HRWR, or any combination thereof.
[0353] In certain embodiments, the invention provides a method for
producing a cement mix, e.g., hydraulic cement mix comprising (i)
contacting a cement mix, e.g., hydraulic cement mix in a mixer with
carbon dioxide while the cement mix, e.g., hydraulic cement mix is
mixing, wherein the carbon dioxide is exposed to the cement mix,
e.g., hydraulic cement mix when the w/c ratio of the cement mix,
e.g., hydraulic cement mix is less than or equal to 0.4. In certain
embodiments, the contacting is achieved by directing a flow of
carbon dioxide to the cement mix, e.g., hydraulic cement mix. In
certain aspects of this embodiment, the w/c ratio of the cement
mix, e.g., hydraulic cement mix is 0.05-0.4. The method may further
comprise monitoring a characteristic of the cement mix, e.g.,
hydraulic cement mix, a gas mixture in contact with the cement mix,
e.g., hydraulic cement mix, a component of a cement mix, e.g.,
hydraulic cement mix apparatus, or a component exposed to the
cement mix, e.g., hydraulic cement mix, and modulating the flow of
carbon dioxide according to the characteristic monitored. The
method may comprise (ii) adding an admixture to the cement mix,
e.g., hydraulic cement mix, such as an admixture that modulates the
flowability of the cement mix, e.g., hydraulic cement mix, for
example an admixture to modulate flowability of type and/or amount
as described elsewhere herein.
[0354] In certain embodiments, the invention provides a method for
producing a cement mix, e.g., hydraulic cement mix comprising (i)
contacting a cement mix, e.g., hydraulic cement mix in a mixer with
carbon dioxide while the cement mix, e.g., hydraulic cement mix is
mixing at a first location, and (ii) transporting the cement mix,
e.g., hydraulic cement mix to a second location where the cement
mix, e.g., hydraulic cement mix is used. In certain aspects of this
embodiment, said contacting is achieved by directing a flow of
carbon dioxide to the cement mix, e.g., hydraulic cement mix. The
second location may be at least 0.1 mile from the first location.
The second location may be at least 0.5 mile from the first
location. The method may comprise monitoring a characteristic of
the cement mix, e.g., hydraulic cement mix, a gas mixture in
contact with the cement mix, e.g., hydraulic cement mix, a
component of a cement mix, e.g., hydraulic cement mix apparatus, or
a component exposed to the cement mix, e.g., hydraulic cement mix,
and modulating the flow of carbon dioxide according to the
characteristic monitored. The method may comprise (ii) adding an
admixture to the cement mix, e.g., hydraulic cement mix, such as an
admixture that modulates the flowability of the cement mix, e.g.,
hydraulic cement mix.
[0355] In certain embodiments, the invention provides a method for
producing a cement mix, e.g., hydraulic cement mix comprising (i)
contacting a cement mix, e.g., hydraulic cement mix in a mixer with
carbon dioxide while the cement mix, e.g., hydraulic cement mix is
mixing with a flow of carbon dioxide directed to the cement mix,
e.g., hydraulic cement mix, (ii) monitoring a characteristic of the
cement mix, e.g., hydraulic cement mix, a gas mixture in contact
with the cement mix, e.g., hydraulic cement mix, a component of a
cement mix, e.g., hydraulic cement mix apparatus, or a component
exposed to the cement mix, e.g., hydraulic cement mix; and (iii)
modulating the exposure of the cement mix, e.g., hydraulic cement
mix to the carbon dioxide according to the characteristic monitored
in step (ii). The method may comprise monitoring a carbon dioxide
concentration in a portion of gas adjacent to the cement mix, e.g.,
hydraulic cement mix, e.g., a portion of gas in the mixer, or a
portion of gas outside the mixer. The carbon dioxide concentration
may be monitored by a sensor. The sensor may transmit a signal to a
controller. The controller may process the signal and transmit a
signal to an actuator according to the results of the processing,
for example, an actuator comprising a valve for controlling the
flow of carbon dioxide to contact the cement mix, e.g., hydraulic
cement mix. The method may comprise monitoring a temperature of the
cement mix, e.g., hydraulic cement mix, the mixer, or of another
component exposed to the cement mix, e.g., hydraulic cement mix is
monitored. A temperature of the mixer may be monitored, or a
temperature of the cement mix, e.g., hydraulic cement mix inside
the mixer may be monitored, or a temperature of a portion of the
cement mix, e.g., hydraulic cement mix that is transported outside
the mixer may be monitored, or any combination thereof. The
contacting of the cement mix, e.g., hydraulic cement mix with
carbon dioxide may be modulated according to the temperature
monitored. The contacting of the cement mix, e.g., hydraulic cement
mix with the carbon dioxide may be modulated when the temperature
being monitored, or a combination of temperatures being monitored,
exceeds a threshold value, such as a value determined relative to
the initial temperature of the cement mix, e.g., hydraulic cement
mix before addition of carbon dioxide, such as a threshold value as
described elsewhere herein. Alternatively, the threshold value may
be an absolute value. The temperature may be monitored by a sensor.
The sensor may transmit a signal to a controller. The controller
may process the signal and transmit a signal to an actuator
according to the results of the processing. The actuator may
comprise a controllable valve for controlling the flow of carbon
dioxide to contact the cement mix, e.g., hydraulic cement mix.
[0356] In certain embodiments, the invention provides a method for
producing a cement mix, e.g., hydraulic cement mix comprising (i)
contacting a first portion of cement mix, e.g., hydraulic cement
mix comprising a first portion of water and hydraulic cement in a
mixer while the cement mix, e.g., hydraulic cement mix is mixing;
and (ii) adding a second portion of cement mix, e.g., hydraulic
cement mix to the first portion. In certain aspects of this
embodiment, said contacting is achieved by directing a flow of
carbon dioxide to the first portion of cement mix, e.g., hydraulic
cement mix.
[0357] In certain embodiments, the invention provides a method of
retrofitting an existing cement mix, e.g., hydraulic cement mixing
apparatus comprising a mixer, comprising operably connecting to the
existing cement mix, e.g., hydraulic cement mixing apparatus a
system for contacting a cement mix, e.g., hydraulic cement mix
within the mixer with carbon dioxide during mixing of the cement
mix, e.g., hydraulic cement mix. In certain aspects of this
embodiment, the system to contact the cement mix, e.g., hydraulic
cement mix in the mixer with carbon dioxide comprises a system to
direct a flow of carbon dioxide to the cement mix, e.g., hydraulic
cement mix during mixing of the cement mix, e.g., hydraulic cement
mix. The method may also comprise operably connecting a source of
carbon dioxide to a conduit for delivering the carbon dioxide to
the mixer. The method may also comprise operably connecting the
conduit to the mixer. The system may comprise an actuator for
modulating delivery of carbon dioxide from the source of carbon
dioxide through the conduit. The system may comprise a control
system for controlling the actuator, operably connected to the
actuator. The control system may comprises a timer and a
transmitter for sending a signal to the actuator based on the
timing of the timer. The method may comprise connecting the
actuator to an existing control system for the cement mix, e.g.,
hydraulic cement mixing apparatus. The method may comprise
modifying the existing control system to control the actuator. The
actuator may be operably connected to or configured to be operably
connected to the conduit, the mixer, a control system for the
mixer, or to a source of carbon dioxide, or a combination thereof.
The actuator may control a valve so as to control delivery of
carbon dioxide to the mixer. The method may comprise adding to the
existing cement mix, e.g., hydraulic cement mixing apparatus one or
more sensors operably connected to, or configured to be operably
connected to, a control system, for monitoring one or more
characteristics of the cement mix, e.g., hydraulic cement mix, a
gas mixture in contact with the cement mix, e.g., hydraulic cement
mix, a component of the cement mix, e.g., hydraulic cement mixing
apparatus, or a component exposed to the cement mix, e.g.,
hydraulic cement mix, for example, one or more sensors is a sensor
for monitoring carbon dioxide concentration of a gas or a
temperature.
IV. Apparatus and Systems
[0358] In one aspect, the invention provides apparatus and systems.
The apparatus may include one or more of a conduit for supplying
carbon dioxide from a carbon dioxide source to a mixer, a source of
carbon dioxide, a mixer, one or more sensors, one or more
controllers, one or more actuators, all as described herein.
[0359] For example, in certain embodiments the invention provides
an apparatus for addition of carbon dioxide to a mixture comprising
hydraulic cement, where the apparatus comprises a mixer for mixing
the cement mix, e.g., hydraulic cement mix, and a system for
delivering carbon dioxide to the cement mix, e.g., hydraulic cement
mix in the mixer during mixing. In certain embodiments, the system
for delivering carbon dioxide is configured to deliver carbon
dioxide to the surface of the cement mix, e.g., hydraulic cement
mix during mixing. The system may include a carbon dioxide source,
a conduit operably connecting the source and the mixer for delivery
of carbon dioxide to the mixer, a metering system for metering flow
of carbon dioxide in the conduit, and an adjustable valve to adjust
the flow rate. In addition, the apparatus may include one or more
sensors to sense carbon dioxide content of gas in the mixer, or
outside the mixer. The apparatus may also include one or more
sensors for sensing the temperature of the cement mix, e.g.,
hydraulic cement mix, or the mixer or other component. The
apparatus may further include a controller that is operably
connected to the one or more sensors, e.g., to one or more
temperature sensors, one or more carbon dioxide sensors, or a
combination thereof, and which is configured to receive data from
the one or more sensors. The controller may be configured to
display the data, e.g., so that a human operator may adjust flow or
other parameters based on the data. The controller may be
configured to perform one or more operations on the data, and to
send output to one or more actuators based on the results of the
one or more operations. For example, the controller may be
configured to send output to a an adjustable valve causing it to
modulate the flow of carbon dioxide in the conduit, e.g., to stop
the flow after a particular temperature, or carbon dioxide
concentration, or both, has been achieved.
[0360] In certain embodiments the invention provides a system for
retrofitting an existing cement mix, e.g., hydraulic cement mix
apparatus to allow carbon dioxide to be contacted with a cement
mix, e.g., hydraulic cement mix during mixing. The system may be
configured to be transported from a site remote from the site of
the existing cement mix, e.g., hydraulic cement mix apparatus to
the site of the existing cement mix, e.g., hydraulic cement mix
apparatus.
[0361] In certain embodiments the invention provides an apparatus
for carbonating a cement mix comprising a cement binder and
aggregate in a cement mix apparatus during a mix operation,
comprising (i) a mixer for mixing the cement mix; (ii) a system for
contacting the cement mix in the mixer with carbon dioxide operably
connected to the mixer and comprising an actuator for modulating a
flow of carbon dioxide to the mixer; (iii) a sensor positioned and
configured to monitor a characteristic of the mix operation; and to
transmit information regarding the characteristic to a controller;
(iv) the controller, wherein the controller is configured (e.g.,
programmed) to process the information and determine whether or not
and/or to what degree to modulate the flow of carbon dioxide to the
mixer and to transmit a signal to the actuator to modulate the flow
of carbon dioxide to the mixer. In addition to, or instead of, the
actuator for modulating a flow of carbon dioxide, the system may
include one or more actuators for modulating another characteristic
of the system, and the controller may be configured to determine
whether or not and to what degree to modulate the other
characteristic, and transmit a signal to the actuator for
modulating the other characteristic.
[0362] The mixer may be any suitable mixer so long as it can be
configured with the remaining elements of the apparatus, such as
mixers described herein. In certain embodiments, the mixer is a
stationery mixer, such as a mixer used in a precast operation. In
certain embodiments, the mixer is a transportable mixer, such as
the drum of a ready mix truck. In embodiments in which the mixer is
transportable, one or more of the elements of the control system
for contacting the cement mix with carbon dioxide, sensing a
characteristic, controlling one or more characteristics such as
carbon dioxide flow, and actuators, may be configured to be
transported along with the mixer, or may be configured to be
detachable from the mixer, for example, to remain at a batching
station for a ready mix truck. See, e.g. FIGS. 3 and 4, which show
elements of the carbon dioxide delivery system in either
non-transportable or transportable form. Elements of the control
system may be similarly transportable or non-transportable. It will
be appreciated that some parts of the system may be transported
while others remain at, e.g. the batching station. For example, all
carbon dioxide may be delivered at the batching station but certain
characteristics of the cement mix, e.g., rheology, may be monitored
while the truck in en route to the job site, and, if necessary, the
cement mix may be modulated based on the monitoring, e.g., by
addition of an admixture, or water, etc.
[0363] The system for contacting the cement mix in the mixer with
carbon dioxide may be any suitable system, such as the systems
described herein. In certain embodiments, the system is configured
to deliver gaseous carbon dioxide to the cement mix. In certain
embodiments, the system is configured to deliver liquid carbon
dioxide to the cement mix in such a manner that the liquid carbon
dioxide is converted to gaseous and solid carbon dioxide as it is
delivered to the cement mix, as described herein. The system may be
configured to deliver carbon dioxide to the surface of the mixing
cement mix, or underneath the surface, or a combination thereof. In
the case of a ready mix truck, the system for contacting the cement
in the mixer with carbon dioxide may share a conduit with the water
delivery system, by a T junction in the conduit, such that either
water or carbon dioxide can be delivered to a final common conduit.
See Examples 2 and 6.
[0364] The sensor may be any suitable sensor so long as it is
configured and positioned to transmit relevant information to the
controller. In certain embodiments, the characteristic of the mix
operation that is monitored by the sensor comprises a
characteristic of the cement binder, the cement mix, a gas mixture
in contact with the cement mix or the mixer, or a component of the
cement mix apparatus. In certain embodiments, the sensor is
configured and positioned to monitor (a) mass of cement binder
added to the cement mix, (b) location of the cement binder in the
mix apparatus, (c) carbon dioxide content of a gas mixture within
the mixer in contact with the cement mix, (d) carbon dioxide
content of a gas mixture exiting from the mixer, (e) carbon dioxide
content of gas mixture in the vicinity of the mix apparatus, (f)
temperature of the cement mix or a component of the mix apparatus
in contact with the cement mix, (g) rheology of the cement mix, (h)
moisture content of the cement mix, or (i) pH of the cement mix. In
certain embodiments, the characteristic monitored by the sensor
comprises carbon dioxide content of a gas mixture exiting from the
mixer; this can be monitored by a single sensor or by a plurality
of sensors placed at various leak locations, in which case the
controller uses information from the plurality of sensors. The
controller can be configured to send a signal to the actuator to
modulate the flow of carbon dioxide when the carbon dioxide content
of the gas mixture reaches a threshold value. Alternatively, or in
addition, the controller can be configured to send a signal to the
actuator to modulate the flow of carbon dioxide when a rate of
change of the carbon dioxide content of the gas mixture reaches a
threshold value. In certain embodiments, the characteristic
monitored by the sensor comprise the temperature of the cement mix
or a component of the mix apparatus in contact with the cement mix.
The controller can be configured to send a signal to the actuator
to modulate the flow of carbon dioxide when the temperature of the
cement mix or a component of the mix apparatus in contact with the
cement mix reaches a threshold value. Alternatively, or in
addition, the controller can be configured to send a signal to the
actuator to modulate the flow of carbon dioxide when a rate of
change of the temperature of the cement mix or a component of the
mix apparatus in contact with the cement mix reaches a threshold
value.
[0365] In certain embodiments, the apparatus comprises a plurality
of sensors configured to monitor a plurality of characteristics a
plurality of characteristics of the cement binder, the cement mix,
a gas mixture in contact with the cement mix or the mixer, or a
component of the cement mix apparatus e.g., at least 2, 3, 4, 5, 6,
7, 8, 9, or 10 characteristics, for example, at least 2 of (i) mass
of cement binder added to the cement mix, (ii) location of the
cement binder in the mixer, (iii) carbon dioxide content of a gas
mixture within the mixer in contact with the cement mix, (iv)
carbon dioxide content of gas mixture exiting from the mixer, (v)
carbon dioxide content of gas mixture in the vicinity of the mixer,
(vi) temperature of the cement mix or a component in contact with
the cement mix, (vii) rheology of the cement mix, (viii) moisture
content of the cement mix. In certain embodiments, a plurality of
sensors is configured and positioned to monitor at least 3 of (i)
mass of cement binder added to the cement mix, (ii) location of the
cement binder in the mixer, (iii) carbon dioxide content of a gas
mixture within the mixer in contact with the cement mix, (iv)
carbon dioxide content of gas mixture exiting from the mixer, (v)
carbon dioxide content of gas mixture in the vicinity of the mixer,
(vi) temperature of the cement mix or a component in contact with
the cement mix, (vii) rheology of the cement mix, (viii) moisture
content of the cement mix. In certain embodiments, a plurality of
sensors is configured and positioned to monitor at least 4 of (i)
mass of cement binder added to the cement mix, (ii) location of the
cement binder in the mixer, (iii) carbon dioxide content of a gas
mixture within the mixer in contact with the cement mix, (iv)
carbon dioxide content of gas mixture exiting from the mixer, (v)
carbon dioxide content of gas mixture in the vicinity of the mixer,
(vi) temperature of the cement mix or a component in contact with
the cement mix, (vii) rheology of the cement mix, (viii) moisture
content of the cement mix. In certain embodiments, a plurality of
sensors is configured and positioned to monitor at least 5 of (i)
mass of cement binder added to the cement mix, (ii) location of the
cement binder in the mixer, (iii) carbon dioxide content of a gas
mixture within the mixer in contact with the cement mix, (iv)
carbon dioxide content of gas mixture exiting from the mixer, (v)
carbon dioxide content of gas mixture in the vicinity of the mixer,
(vi) temperature of the cement mix or a component in contact with
the cement mix, (vii) rheology of the cement mix, (viii) moisture
content of the cement mix. In certain embodiments, a plurality of
sensors is configured and positioned to monitor at least 6 of (i)
mass of cement binder added to the cement mix, (ii) location of the
cement binder in the mixer, (iii) carbon dioxide content of a gas
mixture within the mixer in contact with the cement mix, (iv)
carbon dioxide content of gas mixture exiting from the mixer, (v)
carbon dioxide content of gas mixture in the vicinity of the mixer,
(vi) temperature of the cement mix or a component in contact with
the cement mix, (vii) rheology of the cement mix, (viii) moisture
content of the cement mix.
[0366] In addition to these sensors, or alternatively, the
apparatus may include one or more sensors to monitor the time of
exposure of the cement mix to the carbon dioxide, the flow rate of
the carbon dioxide, or both. For example, a sensor may signal when
a valve to supply carbon dioxide has opened, and, e.g., the flow
rate of the carbon dioxide, and a timer circuit in the controller
can determine total carbon dioxide dose.
[0367] Sensors may be wired to the controller or may transmit
information wirelessly, or any combination thereof.
[0368] The apparatus may additionally, or alternatively, include an
actuator configured to modulate an additional characteristic of the
mix operation, where the actuator is operably connected to the
controller and wherein the controller is configured to send a
signal to the actuator to modulate the additional characteristic
based on the processing of information from one or more sensors.
This actuator can be configured to modulate addition of admixture
to the cement mix, type of admixture added to the cement mix,
timing of addition of admixture to the cement mix, amount of
admixture added to the cement mix, amount of water added to the
cement mix, timing of addition of water to the cement mix, or
cooling the cement mix during or after carbon dioxide addition. In
certain embodiments, the apparatus comprises a plurality of such
actuators, such as at least 2, 3, 4, 5, 6, 7, or 8 such
actuators.
[0369] The actuators may be wired to the controller, or may receive
signals from the controller wirelessly.
[0370] The controller may be any suitable controller so long as it
is capable of being configured to receive information from one or
more sensors, process the information to determine if an output is
required, and transmit signals to one or more actuators, as
necessary, based on the processing; e.g., a computer. For example,
the controller can be a Programmable Logic Controller (PLC),
optionally with a Human Machine Interface (HMI), as described
elsewhere herein. The controller may be located onsite with the
mixer, or it may be remote, e.g., a physical remote controller or a
Cloud-based controller. In certain embodiments, the controller is
configured to store and process the information obtained regarding
the characteristic monitored by the sensor for a first batch of
cement mix and to adjust conditions for a subsequent second cement
mix batch based on the processing to optimize one or more aspects
of the mix operation. For example, the controller may adjust the
second mix recipe, e.g., amount of water used or timing of water
addition, or carbon dioxide exposure in the second batch to improve
carbon dioxide uptake, or to improve rheology or other
characteristics of the mix. In such embodiments in which one or
more conditions of a second mix operation are adjusted, in certain
embodiments the one or more conditions of the second mix operation
includes (a) total amount of carbon dioxide added to the cement
mix, (b) rate of addition of carbon dioxide, (c) time of addition
of carbon dioxide to the cement mix, (d) whether or not an
admixture is added to the cement mix, (e) type of admixture added
to the cement mix, (f) timing of addition of admixture to the
cement mix, (g) amount of admixture added to the cement mix, (h)
amount of water added to the cement mix, (i) timing of addition of
water to the cement mix, (j) cooling the cement mix during or after
carbon dioxide addition, or a combination thereof. The controller
can also receive additional information regarding one or more
characteristics of the cement mix measured after the cement mix
leaves the mixer, and adjusts conditions for the second cement mix
batch based on processing that further comprises the additional
information. In certain embodiments, the one or more
characteristics of the cement mix measured after the cement mix
leaves the mixer comprises (a) rheology of the cement mix at one or
more time points, (b) strength of the cement mix at one or more
time points, (c) shrinkage of the cement mix, (d) water absorption
of the cement mix, or a combination thereof. Other characteristics
include water content, carbon dioxide analysis to confirm carbon
dioxide uptake, calcite content (e.g., as determined by infrared
spectroscopy), elastic modulus, density, and permeability. Any
other suitable characteristic may be measured.
[0371] In embodiments in which a controller adjusts conditions for
a second mix operation based on input from a first mix operation,
the second mix operation may be in the same mix facility or it may
be in a different mix facility. In certain embodiments, the
controller, one or more sensors, one or more actuators, or
combination thereof, transmits information regarding the
characteristics monitored and conditions modulated to a central
controller that receives information from a plurality of
controllers, sensors, actuators, or combination thereof, each of
which transmits information from a separate mixer and mix operation
to the central controller. In these embodiments, the apparatus may
include a second controller that is the central controller, or the
central controller may be the only controller for the apparatus.
Thus, for example, a first mix facility may have a first sensor to
monitor a first characteristic of the first mix operation, and a
second mix facility may have a second sensor to monitor a second
characteristic of a second mix operation, and both may send
information regarding the first and second characteristics to a
central controller, which processes the information and transmit a
signal to the first, second, or even a third, fourth, fifth, etc.,
mix operation to adjust conditions based on the first and second
signals from the first and second sensors. Additional information
that will be typically transmitted to the central controller
includes mix components for the mixes at the first and second mix
operations (e.g., type and amount of cement binder, amount of water
and w/c ratio, types and amounts of aggregate, whether aggregate
was wet or dry, admixtures, and the like) amount, rate, and timing
of carbon dioxide addition, and any other characteristic of the
first and second mix operations that would be useful for
determining conditions to modulate future mix operations based on
the characteristics achieved in past mix operations. Any number of
mix operations may input information to the central controller,
e.g., at least 2, 3, 4, 5, 6, 7, 8, 9, or 10 mix operations, or at
least 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, or 100 mix
operations. The central controller may also receive any other
information that may be suitable to informing decisions regarding
mix operations to optimize one or more conditions of the mix
operation and/or of the cement mix produced in the operation. For
example, the central controller may receive information from
experiments conducted with various types of cements (e.g., various
types of Portland cements) carbonated under various conditions,
and/or exposed to various admixtures, such as at different times,
or in different concentrations, and the like, and the resulting
characteristics of the cement mix, such as rheology at one or more
timepoints, strength at one or more timepoints, and the like. Any
other suitable information, such as information published in
literature, or obtained in any manner, may be input into the
central controller, e.g., automatically and/or through a Human
Machine Interface. The information the central controller receives
can be processed and used to adjust cement mix operations at any
mix operation to which the central controller can transmit outputs.
Thus, the central controller can learn from numerous mix operations
to optimize future operations and, over time, can accumulate a
database to inform decisions in mix operations at a mix site even
if a particular mix recipe and/or conditions have never been used
at that site, or even predict optimum conditions for a mix recipe
that has not been used at any of the sites to which the controller
is connected. The central controller can match to past mix recipes,
or predict optimum conditions for a new mix recipe based on
suitable algorithms using information in its database, or both.
[0372] In certain embodiments in which the controller adjusts a
second mix operation based on characteristics monitored in a first
mix operation, the one or more characteristics of the mix operation
may comprise total amount of carbon dioxide added to the cement
mix, rate of addition of carbon dioxide, time of addition of carbon
dioxide to the cement mix, whether or not an admixture is added to
the cement mix, type of admixture added to the cement mix, timing
of addition of admixture to the cement mix, amount of admixture
added to the cement mix, amount of water added to the cement mix,
timing of addition of water to the cement mix, cooling the cement
mix during or after carbon dioxide addition, or a combination
thereof.
[0373] The controller can be further configured, e.g., programmed,
to receive and process information regarding one or more
characteristics of the cement mix measured after the cement mix
leaves the mixer, and to transmit signals to one or more actuators
configured to adjust conditions for the second cement mix batch
based on the processing to improve contact with the carbon dioxide
or another characteristic of the mix operation in the second mix
operation. The one or more characteristics of the cement mix
measured after the cement mix leaves the mixer can be rheology of
the cement mix at one or more time points, strength of the cement
mix at one or more time points, water absorption, shrinkage, and
the like. The characteristic monitored can depend on the
requirements for a particular mix batch, although other
characteristics may also be monitored to provide data to the
controller for future batches in which those characteristics would
be required.
[0374] The use of an apparatus that includes a control system,
whether for a single mix operation or for a plurality of mix
operations, can produce very high efficiencies of carbon dioxide
uptake (ratio of carbon dioxide or carbon dioxide derivatives in
the cement mix to total carbon dioxide delivered). In certain
embodiments, the apparatus is configured to control one or more
actuators such that an efficiency of carbonation of at least 60,
70, 80, 90, 95, 96, 97, 98, 99, or 99.5% is achieved. Such high
efficiencies allow for greater sequestration of greenhouse gas
without leakage into the atmosphere, as well as a more economical
operation.
[0375] In certain embodiments, the invention provides a controller
for controlling a cement mix mixing operation comprising
carbonation of the cement mix in a mixer by exposing the cement mix
to carbon dioxide, where the controller comprises (i) an input port
for receiving a signal from a sensor that monitors a characteristic
of the cement mix mixing operation; (ii) a processor for processing
the signal from the sensor and formulating an output signal to
modulate the exposure of the cement mix to carbon dioxide or to
modulate a characteristic of the cement mix; and (iii) an output
port for transmitting the output signal to an actuator that
modulates the exposure of the cement mix to carbon dioxide or that
modulates a characteristic of the cement mix. The input and output
ports may be configured to be wired to the sensor or actuator, or
to receive a wireless signal, or a combination of such ports may be
used. In certain embodiments, the input port is configured to
receive a plurality of signals from a plurality of sensors, and the
processor is configured to process the plurality of signals and
formulate an output signal to modulate the exposure of the cement
mix to carbon dioxide or to modulate a characteristic of the cement
mix. Thus, the input port may include a plurality separate ports
that are wired to various sensors, or a wireless port that is
configured to receive signals from a plurality of sensors, or a
combination of one or more wired and wireless ports for one or more
sensors. The controller can be is configured to formulate a
plurality of output signals to modulate the exposure of the cement
mix to carbon dioxide or to modulate a characteristic of the cement
mix and the output port is configured to transmit the plurality of
signals. Similar to an input port for a plurality of signals, this
can be a wired output port with a plurality of ports, a wireless
port configured to send a plurality of signals, or a combination of
wired and wireless ports to send one or more signals each.
[0376] The controller may be configured to process any signal from
any suitable sensor, such as described herein, and to send output
to any suitable actuator, such as described herein. The controller
may also be configured to send information to a central controller,
or may itself be a central controller that is configured to receive
input from, and send output to, a plurality of mix operations, also
as described herein.
[0377] In certain embodiments, the invention provides a network
comprising a plurality of spatially separate cement mix operations,
such as at least 2, 3, 4, 5, 6, 7, 8, 9, or 10, or at least 20, 30,
40, 50, 70, or 100 separate mix operations, each of which comprises
at least one sensor for monitoring at least one characteristic of
its operation, and comprising a central processing unit, to which
each sensor sends its information and which stores and/or processes
the information. Alternatively, or in addition, information
regarding at least one characteristic of the mix operation may be
input manually into the central processing unit, e.g., through a
HMI. One or more of the mix operations may be a mix operation in
which the cement mix is carbonated, e.g., as described herein, such
as a mix operation in which the cement is carbonated, i.e., exposed
to carbon dioxide in such a way that the carbon dioxide is taken up
by the cement mix, during mixing. The mix operations may also
include sensors or other elements by which one or more
characteristics of the cement mix is monitored, before, during, or
after mixing, e.g., also as described herein, which transmit
information to the central processor. The central processor may
also be configured to output signals to one or more of the mix
operations, or to other mix operations, based on the processing of
the signals.
[0378] In certain embodiments, the invention provides an apparatus
for producing a cement mix, e.g., hydraulic cement mix comprising
(i) a mixer for mixing a cement mix, e.g., hydraulic cement mix;
and (ii) a system for exposing the cement mix, e.g., hydraulic
cement mix to carbon dioxide during mixing, wherein the system is
configured to deliver carbon dioxide to the surface of the cement
mix, e.g., hydraulic cement mix.
[0379] In certain embodiments, the invention provides an apparatus
for mixing a cement mix, e.g., hydraulic cement mix comprising (i)
a mixer for mixing the cement mix, e.g., hydraulic cement mix; (ii)
a system for contacting the cement mix, e.g., hydraulic cement mix
with carbon dioxide directed to the cement mix, e.g., hydraulic
cement mix operably connected to the mixer; (iii) a sensor
positioned and configured to monitor one or more characteristics of
the cement mix, e.g., hydraulic cement mix, a gas mixture in
contact with the cement mix, e.g., hydraulic cement mix, a
component of a cement mix, e.g., hydraulic cement mix apparatus, or
a component exposed to the cement mix, e.g., hydraulic cement mix;
and (iv) an actuator operably connected to the sensor for
modulating the flow of the carbon dioxide based on the
characteristic monitored. In certain aspects of this embodiment,
the system for contacting the cement mix, e.g., hydraulic cement
mix with carbon dioxide comprises a system a system for contacting
the cement mix, e.g., hydraulic cement mix with a flow of carbon
dioxide directed to the cement mix, e.g., hydraulic cement mix.
[0380] In certain embodiments, the invention provides an apparatus
for retrofitting an existing cement mix, e.g., hydraulic cement
mixer comprising a conduit configured to be operably connected to a
source of carbon dioxide and to the mixer, for delivering carbon
dioxide from the source to the mixer. The apparatus may comprise
the source of carbon dioxide. The apparatus may comprise an
actuator for controlling delivery of carbon dioxide from a source
of carbon dioxide through the conduit, wherein the actuator is
operably connected or is configured to be operably connected to a
control system. The apparatus may further comprise the control
system. The control system may comprise a timer and a transmitter
for sending a signal to the actuator based on the timing of the
timer. The control system may be an existing control system for the
mixer. The apparatus may comprise instructions for modifying the
existing control system to control the actuator. The actuator may
be operably connected to or configured to be operably connected to
the conduit, the mixer, a control system for the mixer, or to a
source of carbon dioxide, or a combination thereof. The actuator
may control a valve so as to control delivery of carbon dioxide to
the mixer. The apparatus may comprise one or more sensors operably
connected to, or configured to be operably connected to, the
control system for monitoring one or more characteristics of the
cement mix, e.g., hydraulic cement mix, a gas mixture adjacent to
the cement mix, e.g., hydraulic cement mix, or a component in
contact with the cement mix, e.g., hydraulic cement mix. The one or
more sensors may be a sensor for monitoring carbon dioxide
concentration of a gas or a temperature.
[0381] In certain embodiments, the invention provides a system for
exposing a cement mix, e.g., hydraulic cement mix within a
transportable mixer to carbon dioxide comprising (i) a source of
carbon dioxide that is more than 50% pure carbon dioxide; (ii) a
transportable mixer for mixing a cement mix, e.g., hydraulic cement
mix; and (iii) a conduit operably connected to the source of carbon
dioxide and to the mixer for delivering carbon dioxide from the
source of carbon dioxide to the cement mix, e.g., hydraulic cement
mix. The system may further comprise an actuator operably connected
to the conduit for controlling the flow of the carbon dioxide. The
actuator may comprise a valve. The system may comprise a controller
operably connected to the actuator, where the controller is
configured to operate the actuator based on predetermined
parameters, on feedback from one or more sensors, or a combination
thereof. In certain embodiments the source of carbon dioxide and
the conduit are housed in a portable unit that can be moved from
one readymix site to another, to provide carbon dioxide to more
than one readymix truck.
[0382] In certain embodiments, the invention provides a system for
exposing a cement mix, e.g., hydraulic cement mix within a mixer to
carbon dioxide comprising (i) a source of carbon dioxide; (ii) the
mixer for mixing the cement mix, e.g., hydraulic cement mix; (iii)
a conduit operably connected to the source of carbon dioxide and to
the mixer for delivering carbon dioxide from the source of carbon
dioxide to the cement mix, e.g., hydraulic cement mix; (iv) a
sensor positioned and configured to monitor one or more one or more
characteristics of the cement mix, e.g., hydraulic cement mix, a
gas mixture adjacent to the cement mix, e.g., hydraulic cement mix,
or a component in contact with the cement mix, e.g., hydraulic
cement mix; and (v) an actuator operably connected to the sensor
and to the system for exposing the cement mix, e.g., hydraulic
cement mix to carbon dioxide, wherein the actuator is configured to
alter the exposure of the cement mix, e.g., hydraulic cement mix to
the carbon dioxide based on the characteristic monitored by the
sensor. The mixer may be a stationary mixer. The mixer may be a
transportable mixer.
V. Compositions
[0383] The invention also provides compositions, e.g., compositions
that may be produced by the methods described herein. In certain
embodiment the concrete mix is fluid, that is, capable of being
mixed in the mixer and poured for its intended purpose. In certain
embodiments the invention provides a composition that is a dry
carbonated concrete mix that is fluid and compactable, e.g.,
sufficiently fluid and compactable to be placed in a mold for a
pre-cast concrete product, that comprises hydraulic cement, e.g.,
OPC, and carbon dioxide and/or reaction products of carbon dioxide
with the OPC and/or other components of the mix, and, optionally,
one or more of aggregates and an admixture, such as an admixture to
modulate the compactability of the carbonated concrete mix, and/or
a strength accelerator. In certain embodiments the admixture
comprises a set retarder, such as a sugar or sugar derivative,
e.g., sodium gluconate. In certain embodiments the invention
provides a composition that is a wet carbonated concrete mix that
is fluid and pourable, e.g., sufficiently fluid and pourable to be
poured in a mold at a construction site, that comprises hydraulic
cement, e.g., OPC, and carbon dioxide and/or reaction products of
carbon dioxide with the OPC and/or other components of the mix,
and, optionally, one or more of aggregates and an admixture, such
as an admixture to modulate the flowability of the carbonated
concrete mix, and/or a strength accelerator. In certain embodiments
the admixture comprises a set retarder, such as a sugar or sugar
derivative, e.g., sodium gluconate.
[0384] In some methods, solid carbon dioxide (dry ice) is added to
the cement mix, producing a composition comprising a cement mix,
such as a hydraulic cement mix such as concrete, and solid carbon
dioxide. The solid carbon dioxide may be present in an amount of
greater than 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8,
0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.7, 2.0, or 2.5% bwc, or
0.01-5%, 0.01-2%, 0.01-1%, 0.01-0.5%, 0.1-5%, 0.1-2%, 0.1-1%, or
0.1-0.5%. In certain embodiments the invention provides a cement
mix comprising gaseous carbon dioxide or carbon dioxide reaction
products, such as carbonates, and solid carbon dioxide. The solid
carbon dioxide may be present in an amount of greater than 0.01,
0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2,
1.3, 1.4, 1.5, 1.7, 2.0, or 2.5% bwc or 0.01-5%, 0.01-2%, 0.01-1%,
0.01-0.5%, 0.1-5%, 0.1-2%, 0.1-1%, or 0.1-0.5%. The gaseous carbon
dioxide or carbon dioxide reaction products may be present in an
amount of greater than 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6,
0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.7, 2.0, or 2.5% bwc,
or 0.01-5%, 0.01-2%, 0.01-1%, 0.01-0.5%, 0.1-5%, 0.1-2%, 0.1-1%, or
0.1-0.5%. Carbon dioxide reaction products include carbonic acid,
bicarbonate, and all forms of calcium carbonate (e.g., amorphous
calcium carbonate, vaterite, aragonite, and calcite), as well as
other products formed by the reaction of carbon dioxide with
various components of the cement mix. The solid carbon dioxide may
be added as a single block, or more than one block, such as more
than 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 50, or 100 blocks. In some
embodiments, the solid carbon dioxide is formed from release of
liquid carbon dioxide into the mix.
[0385] The cement mix may contain an admixture, such as any
admixture as described herein, e.g., a carbohydrate or carbohydrate
derivative, such as sodium gluconate. The admixture may be present
in an amount of greater than 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5,
0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.7, 2.0, or
2.5%; or greater than 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6,
0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.7, 2.0, or 2.5% and
less than 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0,
1.1, 1.2, 1.3, 1.4, 1.5, 1.7, 2.0, 2.5 or 3.0%, e.g., any range
that may be expressed as the greater than and less than amounts.
Exemplary ranges include 0.01-3.0%, 0.01-1.5%, 0.01-1%, 0.01-0.5%,
0.01-0.4%, 0.01-0.2%, 0.01-0.1%, 0.1-3.0%, 0.1-1.5%, 0.1-1%,
0.1-0.5%, 0.1-0.4%, 0.1-0.2%, or 0.1-0.1%.
[0386] It has been found that the addition of carbon dioxide to a
cement mix during mixing results in the formation of nanocrystals
of calcium carbonate. Earlier work has shown that adding exogenous
nanocrystalline calcium carbonate (e.g., calcium carbonate with a
particle size in a range of 50-120 nm) to a concrete mix improved
the hydration of the mix; however, when exogenously supplied
calcium carbonate is used, a large quantity, such as 10% bwc, is
needed to achieve the desired effect, probably due to clumping of
the added nanocrystals. In contrast, the calcium carbonate
nanocrystals can be formed in situ, without clumping, and thus a
much greater dispersion can be achieved; i.e., homogeneously
dispersed nanocrystals as opposed to dispersion with clumping.
Without being bound by theory, it is possible that the performance
improvement observed due to the formation of carbonate reaction
products in some carbonate concrete mixes is analogous to growing
an in-situ nanoparticle CaCO.sub.3 addition that would act as
nucleation sites and impact later hydration product
development.
[0387] Thus, for example, in certain embodiments, the incidence of
discrete single nanocrystals of calcium carbonate of less than 500
nm, or less than 400 nm, or less than 300 nm, or less than 200 nm
particle size, such as homogenously dispersed nanocrystals without
clumping, or without substantial clumping, may be over 10, 20, 30,
40, 50, 60, or 80% of the calcium carbonate in the composition.
"Particle size" refers to length of the longest dimension of the
crystals, and may be determined, e.g., by scanning electron
microscopy. The calcium carbonate may comprise less than 5%, 4%,
3%, 2.5%, 2.0%, 1.9%, 1.8%, 1.7%, 1.6% 1.5%, 1.4%, 1.3%, 1.2%,
1.1%, 1.0%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, or 0.1%
bwc of the composition, e.g., cement mix composition such as a
hydraulic cement mix, e.g., concrete composition, in certain
embodiments comprising, e.g., also comprising, at least 0.001%,
0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%,
1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%,
2.2%, 2.3%, 2.4%, 2.5%, 2.7%, 3.0%, or 4.0% bwc of the composition,
e.g., cement mix composition such as a hydraulic cement mix, e.g.,
concrete composition. For example, in certain embodiments the
calcium carbonate comprises 0.001-5.0% bwc of the composition; in
certain embodiments the calcium carbonate comprises 0.001-4.0% bwc
of the composition; in certain embodiments the calcium carbonate
comprises 0.001-3.0% bwc of the composition; in certain
embodiments, the calcium carbonate comprises 0.001-2.5% bwc of the
composition; in certain embodiments the calcium carbonate comprises
0.001-2.0% bwc of the composition; in certain embodiments the
calcium carbonate comprises 0.001-1.5% bwc of the composition; in
certain embodiments the calcium carbonate comprises 0.001-1.3% bwc
of the composition; in certain embodiments the calcium carbonate
comprises 0.001-1.0% bwc of the composition; in certain embodiments
the calcium carbonate comprises 0.001-0.8% bwc of the composition;
in certain embodiments the calcium carbonate comprises 0.001-0.6%
bwc of the composition; in certain embodiments the calcium
carbonate comprises 0.001-0.5% bwc of the composition; in certain
embodiments the calcium carbonate comprises 0.001-0.4% bwc of the
composition; in certain embodiments the calcium carbonate comprises
0.001-0.3% bwc of the composition; in certain embodiments the
calcium carbonate comprises 0.001-0.2% bwc of the composition; in
certain embodiments the calcium carbonate comprises 0.001-0.1% bwc
of the composition; in certain embodiments the calcium carbonate
comprises 0.01-5.0% bwc of the composition; in certain embodiments
the calcium carbonate comprises 0.01-4.0% bwc of the composition;
in certain embodiments the calcium carbonate comprises 0.01-3.0%
bwc of the composition; in certain embodiments the calcium
carbonate comprises 0.01-2.5% bwc of the composition; in certain
embodiments the calcium carbonate comprises 0.01-2.0% bwc of the
composition; in certain embodiments the calcium carbonate comprises
0.01-1.5% bwc of the composition; in certain embodiments the
calcium carbonate comprises 0.01-1.3% bwc of the composition; in
certain embodiments the calcium carbonate comprises 0.01-1.0% bwc
of the composition; in certain embodiments the calcium carbonate
comprises 0.01-0.8% bwc of the composition; in certain embodiments
the calcium carbonate comprises 0.01-0.6% bwc of the composition;
in certain embodiments the calcium carbonate comprises 0.01-0.4%
bwc of the composition; in certain embodiments the calcium
carbonate comprises 0.01-0.3% bwc of the composition; in certain
embodiments the calcium carbonate comprises 0.01-0.2% bwc of the
composition; in certain embodiments the calcium carbonate comprises
0.01-0.1% bwc of the composition; in certain embodiments the
calcium carbonate comprises 0.1-5.0% bwc of the composition; in
certain embodiments the calcium carbonate comprises 0.1-4.0% bwc of
the composition; in certain embodiments the calcium carbonate
comprises 0.1-3.0% bwc of the composition; in certain embodiments
the calcium carbonate comprises 0.1-2.5% bwc of the composition; in
certain embodiments the calcium carbonate comprises 0.1-2.0% bwc of
the composition; in certain embodiments the calcium carbonate
comprises 0.1-1.5% bwc of the composition; in certain embodiments
the calcium carbonate comprises 0.1-1.3% bwc of the composition; in
certain embodiments the calcium carbonate comprises 0.1-1.0% bwc of
the composition; in certain embodiments the calcium carbonate
comprises 0.1-0.8% bwc of the composition; in certain embodiments
the calcium carbonate comprises 0.1-0.6% bwc of the composition; in
certain embodiments the calcium carbonate comprises 0.1-0.4% bwc of
the composition; in certain embodiments the calcium carbonate
comprises 0.1-0.3% bwc of the composition; in certain embodiments
the calcium carbonate comprises 0.1-0.2% bwc of the composition. In
certain embodiments, the composition is a concrete composition
comprising hydraulic cement, e.g., Portland cement, and aggregate,
where the hydraulic cement comprises less than 35%, 30%, 25%, 23%,
20%, 18%, 15%, 13%, or 10% by weight of the concrete composition,
in certain embodiments comprising, e.g., also comprising, at least
5%, 8%, 10%, 13%, 15%, 20%, 23%, 25%, or 30% by weight of the
concrete composition. For example, in certain embodiments the
hydraulic cement comprises 5-35% by weight of the concrete
composition; in certain embodiments the hydraulic cement comprises
5-30% by weight of the concrete composition; in certain embodiments
the hydraulic cement comprises 5-25% by weight of the concrete
composition; in certain embodiments the hydraulic cement comprises
5-23% by weight of the concrete composition; in certain embodiments
the hydraulic cement comprises 5-20% by weight of the concrete
composition; in certain embodiments the hydraulic cement comprises
5-18% by weight of the concrete composition; in certain embodiments
the hydraulic cement comprises 5-15% by weight of the concrete
composition; in certain embodiments the hydraulic cement comprises
10-35% by weight of the concrete composition; in certain
embodiments the hydraulic cement comprises 10-30% by weight of the
concrete composition; in certain embodiments the hydraulic cement
comprises 10-25% by weight of the concrete composition; in certain
embodiments the hydraulic cement comprises 10-23% by weight of the
concrete composition; in certain embodiments the hydraulic cement
comprises 10-20% by weight of the concrete composition; in certain
embodiments the hydraulic cement comprises 10-18% by weight of the
concrete composition; in certain embodiments the hydraulic cement
comprises 10-15% by weight of the concrete composition; in certain
embodiments the hydraulic cement comprises 15-35% by weight of the
concrete composition; in certain embodiments the hydraulic cement
comprises 15-30% by weight of the concrete composition; in certain
embodiments the hydraulic cement comprises 15-25% by weight of the
concrete composition; in certain embodiments the hydraulic cement
comprises 15-23% by weight of the concrete composition; in certain
embodiments the hydraulic cement comprises 15-20% by weight of the
concrete composition; in certain embodiments the hydraulic cement
comprises 15-18% by weight of the concrete composition. The
composition may be a wet concrete composition, for example, a
flowable concrete composition, or it may be a concrete composition
that has undergone set and/or hardening. In certain embodiment, it
can be assumed for purposes of determining calcium carbonate
content of a composition that all carbon dioxide in the composition
has been converted to calcium carbonate, and that a value from a
test for carbonation can be converted to a calcium carbonate value;
for example, if a test of carbonation for a concrete mix shows an
uptake of carbon dioxide of 0.6% bwc, it can be assumed that the
composition is 1.4% bwc of calcium carbonate. Any suitable test for
carbonation may be used, such as those described herein.
[0388] As crystal formation starts, crystal size for at least 10,
20, 30, 40, or 50% of the calcium carbonate in the composition may
be less 100, 80, 60, 50, 40, or 30 nm. In addition, the polymorphic
composition of the crystals may vary, depending on the time the
composition has been reacting, the timing of addition of carbon
dioxide, the use of crystal-modifying admixtures, and the like. In
certain embodiments, at least 1, 5, 10, 20, 30, 40, or 50% of the
calcium carbonate in the composition is amorphous calcium
carbonate, or 0.01-50%, 0.1-50%, 1-50%, 5-50%, 10-50%, or 20-50%.
In certain embodiments, at least 1, 5, 10, 20, 30, 40, or 50% of
the calcium carbonate in the composition is vaterite, 0.01-50%,
0.1-50%, 1-50%, 5-50%, 10-50%, or 20-50%. In certain embodiments,
at least 1, 5, 10, 20, 30, 40, or 50% of the calcium carbonate in
the composition is aragonite, 0.01-50%, 0.1-50%, 1-50%, 5-50%,
10-50%, or 20-50%. In certain embodiments, at least 1, 5, 10, 20,
30, 40, or 50% of the calcium carbonate in the composition is
calcite, or 0.01-99.9%, 0.1-99.9%, 1-99%, 5-99.9%, 10-99.9%,
30-99.9%, 50-99.9%, 0.01-90%, 0.1-90%, 1-90%, 5-90%, 10-90%,
30-90%, 50-90%, 0.01-80%, 0.1-80%, 1-80%, 5-80%, 10-80%, 30-80%,
50-80%. Any combination of amorphous calcium carbonate, vaterite,
aragonite, and/or calcite may also be present, for example at the
indicated percentages.
[0389] Compositions may also include one or more supplementary
cementitious materials (SCMs) and/or cement replacements, as
described elsewhere herein. In certain embodiments, a composition
includes, in addition to cement, one or more SCMS and/or cement
replacements, for example blast furnace slag, fly ash, silica fume,
natural pozzolans (such as metakaolin, calcined shale, calcined
clay, volcanic glass, zeolitic trass or tuffs, rice husk ash,
diatomaceous earth, and calcined shale), waste glass, limestone,
recycled/waste plastic, scrap tires, municipal solid waste ash,
wood ash, cement kiln dust, or foundry sand, at a suitable
percentage of the composition bwc, such as 0.1-100%, or 1-100%, or
5-100%, or 10-100%, or 20-100%, or 30-100%, or 40-100%, or 50-100%,
or 0.1-80%, or 1-80%, or 5-80%, or 10-80%, or 20-80%, or 30-80%, or
40-80%, or 50-80%, or 0.1-50%, or 1-50%, or 5-50%, or 10-50%, or
20-50%, or 30-50%, or 0.1-40%, or 1-40%, or 5-40%, or 10-40%, or
20-40% bwc. In certain embodiments, the composition includes an SCM
and in some of these embodiments the SCM is fly ash, slag, silica
fume, or a natural pozzolan. In certain embodiment, the SCM is fly
ash. In certain embodiments, the SCM is slag. Further embodiments
in which SCM is used are described elsewhere herein.
[0390] Thus, in certain embodiments, the invention provides a fluid
cement mix, e.g., hydraulic cement mix composition comprising (i) a
wet cement mix, e.g., hydraulic cement mix comprising hydraulic
cement and water in a w/c ratio of no more than 0.4, or 0.3, or 0.2
and (ii) carbon dioxide or carbonation product in an amount of at
least 0.05% by weight of cement (bwc). The composition is in a
mixable and/or flowable state, e.g., set and hardening have not
progressed to the point where the mixture can no longer be mixed by
the apparatus in which it is formed. The composition may further
comprise (ii) an admixture for modulating the flowability of the
cement mix, e.g., hydraulic cement mixture. The admixture may a
polycarboxylate superplasticer, a naphthalene HRWR, or a
combination thereof.
[0391] In certain embodiments, the invention provides a fluid
cement mix, e.g., hydraulic cement mix composition comprising (i) a
wet cement mix, e.g., hydraulic cement mix comprising hydraulic
cement and water; (ii) carbon dioxide or carbonation product in an
amount of at least 0.05% bwc; (iii) an admixture for modulating the
flowability of the wet hydraulic cement mix. In certain embodiments
the admixture comprises a polycarboxylate superplasticer, a
naphthalene HRWR, or any combination thereof.
[0392] In certain embodiments, the invention provides a cement mix,
e.g., hydraulic cement mix composition, which may be a fluid cement
mix, comprising (i) a wet cement mix, e.g., hydraulic cement mix
comprising hydraulic cement and water; (ii) carbon dioxide in
solid, liquid, and/or gaseous form, or in aqueous solution as
carbonic acid or bicarbonate, in an amount of 0.01-2% bwc; (iii)
solid calcium carbonate in an amount of 0.01-2% bwc; and (iii) a
supplementary cementitious material and/or cement replacement. In
certain embodiments, the carbon dioxide comprises carbon dioxide in
solid form. During mixing and later set and hardening, various
intermediate compositions are produced, so that initial
compositions may contain mostly carbon dioxide in gaseous, liquid,
solid form or in solution with little calcium carbonate formation,
and later compositions may contain mostly calcium carbonate with
little carbon dioxide in gaseous, liquid, solid form or in
solution. In certain embodiments, the SCM and/or cement replacement
comprises 0.1-50%, or 1-50%, or 5-50%, or 10-50%, or 20-50%, or
1-40%, or 5-40%, or 10-50%, or 20-40% bwc in the composition. In
certain embodiments, the SCM and/or cement replacement is blast
furnace slag, fly ash, silica fume, natural pozzolans (such as
metakaolin, calcined shale, calcined clay, volcanic glass, zeolitic
trass or tuffs, rice husk ash, diatomaceous earth, and calcined
shale), limestone, waste glass, recycled/waste plastic, scrap
tires, municipal solid waste ash, wood ash, cement kiln dust, or
foundry sand, or a combination thereof. In certain embodiments, an
SCM is used and in certain of these embodiments, the SCM is blast
furnace slag, fly ash, silica fume, or natural pozzolan, or a
combination thereof. In certain embodiments, the SCM is blast
furnace slag. In certain embodiments, the SCM is fly ash. In
certain embodiments, the SCM is silica fume. In certain
embodiments, the SCM is a natural pozzolan. In certain embodiments
the hydraulic cement is Portland cement. The composition may
further comprise an admixture. In certain embodiments, the
admixture is a carbohydrate or carbohydrate derivative, such as
sodium gluconate. The admixture may be present at any suitable
concentration, such as 0.01-2%, or 0.01-1%, or 0.01-0.5%, or
0.01-0.4%, or 0.01-0.3%, or 0.01-0.2%, or 0.01-0.1%. The
polymorphic composition of the calcium carbonate may include any of
the polymorphs described herein. In certain embodiments, at least
1, 5, 10, 20, 30, 40, or 50% of the calcium carbonate in the
composition is amorphous calcium carbonate, or 0.01-50%, 0.1-50%,
1-50%, 5-50%, 10-50%, or 20-50%. In certain embodiments, at least
1, 5, 10, 20, 30, 40, or 50% of the calcium carbonate in the
composition is vaterite, or 0.01-50%, 0.1-50%, 1-50%, 5-50%,
10-50%, or 20-50%. In certain embodiments, at least 1, 5, 10, 20,
30, 40, or 50% of the calcium carbonate in the composition is
aragonite, or 0.01-50%, 0.1-50%, 1-50%, 5-50%, 10-50%, or 20-50%.
In certain embodiments, at least 1, 5, 10, 20, 30, 40, or 50% of
the calcium carbonate in the composition is calcite, or 0.01-99.9%,
0.1-99.9%, 1-99%, 5-99.9%, 10-99.9%, 30-99.9%, 50-99.9%, 0.01-90%,
0.1-90%, 1-90%, 5-90%, 10-90%, 30-90%, 50-90%, 0.01-80%, 0.1-80%,
1-80%, 5-80%, 10-80%, 30-80%, 50-80%. Any combination of amorphous
calcium carbonate, vaterite, aragonite, and/or calcite may also be
present, for example at the indicated percentages.
[0393] In certain embodiments, the invention provides a set or
hardened cement mix, e.g., hydraulic cement mix composition such as
a set or hardened concrete, comprising (i) reaction products formed
in a wet cement mix, e.g., hydraulic cement mix comprising
hydraulic cement and water, such as reaction products of a Portland
cement mix; (iii) calcium carbonate in an amount of 0.01-5% bwc, or
0.01-2% bwc, where the calcium carbonate is present as crystals or
particles wherein at least 10, 20, 50, 70, or 90% of the particles
are less than 1 um, or less than 500 nm, or less than 400 nm, or
less than 200 nm in average dimension; and (iii) a supplementary
cementitious material and/or cement replacement and/or reaction
products of supplementary cementitious material or cement
replacement. In certain embodiments, the SCM and/or cement
replacement comprises 0.1-50%, or 1-50%, or 5-50%, or 10-50%, or
20-50%, or 1-40%, or 5-40%, or 10-50%, or 20-40% bwc in the
composition. In certain embodiments, the SCM and/or cement
replacement is blast furnace slag, fly ash, silica fume, natural
pozzolans (such as metakaolin, calcined shale, calcined clay,
volcanic glass, zeolitic trass or tuffs, rice husk ash,
diatomaceous earth, and calcined shale), limestone, waste glass,
recycled/waste plastic, scrap tires, municipal solid waste ash,
wood ash, cement kiln dust, or foundry sand, or a combination
thereof. In certain embodiments, an SCM is used and in certain
embodiments, the SCM is blast furnace slag, fly ash, silica fume,
or natural pozzolan, or a combination thereof. In certain
embodiments, the SCM is blast furnace slag. In certain embodiment,
the SCM is fly ash. In certain embodiments, the SCM is silica fume.
In certain embodiments, the SCM is a natural pozzolan. In certain
embodiments the hydraulic cement or reaction products is Portland
cement or Portland cement reaction products. The composition may
further comprise an admixture. In certain embodiments, the
admixture is a carbohydrate or carbohydrate derivative, such as
sodium gluconate. The admixture may be present at any suitable
concentration, such as 0.01-2%, or 0.01-1%, or 0.01-0.5%, or
0.01-0.4%, or 0.01-0.3%, or 0.01-0.2%, or 0.01-0.1%. The
polymorphic composition of the calcium carbonate may include any of
the polymorphs described herein. In certain embodiments, at least
1, 5, 10, 20, 30, 40, or 50% of the calcium carbonate in the
composition is amorphous calcium carbonate, or 0.01-50%, 0.1-50%,
1-50%, 5-50%, 10-50%, or 20-50%. In certain embodiments, at least
1, 5, 10, 20, 30, 40, or 50% of the calcium carbonate in the
composition is vaterite, or 0.01-50%, 0.1-50%, 1-50%, 5-50%,
10-50%, or 20-50%. In certain embodiments, at least 1, 5, 10, 20,
30, 40, or 50% of the calcium carbonate in the composition is
aragonite, or 0.01-50%, 0.1-50%, 1-50%, 5-50%, 10-50%, or 20-50%.
In certain embodiments, at least 1, 5, 10, 20, 30, 40, or 50% of
the calcium carbonate in the composition is calcite, or 0.01-99.9%,
0.1-99.9%, 1-99%, 5-99.9%, 10-99.9%, 30-99.9%, 50-99.9%, 0.01-90%,
0.1-90%, 1-90%, 5-90%, 10-90%, 30-90%, 50-90%, 0.01-80%, 0.1-80%,
1-80%, 5-80%, 10-80%, 30-80%, 50-80%. Any combination of amorphous
calcium carbonate, vaterite, aragonite, and/or calcite may also be
present, for example at the indicated percentages.
[0394] In certain embodiments, the invention provides a cement mix,
e.g., hydraulic cement mix composition, which may be a fluid cement
mix, comprising (i) a wet cement mix, e.g., hydraulic cement mix
comprising hydraulic cement and water; (ii) calcium carbonate that
is nanocrystalline where the incidence of discrete single
nanocrystals of less than 500 nm, or less than 400 nm, or less than
300 nm, or less than 200 nm, or less than 100 nm, or less than 50
nm particle size is over 10, 20, 30, 40, 50, 60, or 80% of the
calcium carbonate; and (iii) a supplementary cementitious material
and/or cement replacement. It will be appreciated that the
nanocrystalline character of the composition as a whole may be
determined by assaying the nanocrystalline character of one or more
representative samples. In certain embodiments, the nanocrystalline
calcium carbonate comprises 0.01-5%, or 0.01-2%, or 0.01-1%, or
0.01-0.5%, or 0.01-0.4%, or 0.01-0.3%, or 0.01-0.02%, or 0.01-0.1%
of the composition bwc. In certain embodiments, the SCM and/or
cement replacement comprises 0.1-50%, or 1-50%, or 5-50%, or
10-50%, or 20-50%, or 1-40%, or 5-40%, or 10-50%, or 20-40% bwc. In
certain embodiments, the SCM and/or cement replacement is blast
furnace slag, fly ash, silica fume, natural pozzolans (such as
metakaolin, calcined shale, calcined clay, volcanic glass, zeolitic
trass or tuffs, rice husk ash, diatomaceous earth, and calcined
shale), limestone, waste glass, recycled/waste plastic, scrap
tires, municipal solid waste ash, wood ash, cement kiln dust, or
foundry sand, or a combination thereof. In certain embodiments, an
SCM is used and in certain of these embodiments, the SCM is blast
furnace slag, fly ash, silica fume, or natural pozzolan, or a
combination thereof. In certain embodiments, the SCM is blast
furnace slag. In certain embodiment, the SCM is fly ash. In certain
embodiments, the SCM is silica fume. In certain embodiments, the
SCM is a natural pozzolan. In certain embodiments the hydraulic
cement is Portland cement. The composition may further comprise an
admixture. In certain embodiments, the admixture is a carbohydrate
or carbohydrate derivative, such as sodium gluconate. The admixture
may be present at any suitable concentration, such as 0.01-2%, or
0.01-1%, or 0.01-0.5%, or 0.01-0.4%, or 0.01-0.3%, or 0.01-0.2%, or
0.01-0.1%. The polymorphic composition of the nanocrystals may
include any of the polymorphs described herein. In certain
embodiments, at least 1, 5, 10, 20, 30, 40, or 50% of the calcium
carbonate nanocrystals in the composition is amorphous calcium
carbonate nanocrystals, or 0.01-50%, 0.1-50%, 1-50%, 5-50%, 10-50%,
or 20-50%. In certain embodiments, at least 1, 5, 10, 20, 30, 40,
or 50% of the calcium carbonate nanocrystals in the composition is
vaterite nanocrystals, or 0.01-50%, 0.1-50%, 1-50%, 5-50%, 10-50%,
or 20-50%. In certain embodiments, at least 1, 5, 10, 20, 30, 40,
or 50% of the calcium carbonate nanocrystals in the composition is
aragonite nanocrystals, 0.01-50%, 0.1-50%, 1-50%, 5-50%, 10-50%, or
20-50%. In certain embodiments, at least 1, 5, 10, 20, 30, 40, or
50% of the calcium carbonate nanocrystals in the composition is
calcite nanocrystals, or 0.01-99.9%, 0.1-99.9%, 1-99%, 5-99.9%,
10-99.9%, 30-99.9%, 50-99.9%, 0.01-90%, 0.1-90%, 1-90%, 5-90%,
10-90%, 30-90%, 50-90%, 0.01-80%, 0.1-80%, 1-80%, 5-80%, 10-80%,
30-80%, 50-80%. Any combination of amorphous calcium carbonate,
vaterite, aragonite, and/or calcite may also be present, for
example at the indicated percentages. It will be appreciated that
the polymorphic makeup of the composition as a whole may be
estimated by the polymorphic makeup of one or more representative
samples of the composition.
EXAMPLES
Example 1
[0395] This example describes contacting a wet hydraulic cement mix
(concrete) with carbon dioxide during mixing of the concrete.
[0396] A series of tests were conducted to contact wet concrete mix
with carbon dioxide during mixing of the concrete.
[0397] In a first experiment, bagged readymix concrete (Quikrete or
Shaw), 20 kg was mixed with water in a Hobart mixer. The cement
content of the concrete was not known but was assumed to be 12-14%.
A value of 14% was used in subsequent calculations. 0.957 kg of
water, which was 57% of the final water, was added for a w/c ratio
of 0.34 and the mixer was topped with a loose lid. The concrete mix
was mixed for 1 minute. Then a gas mixture containing carbon
dioxide at a concentration of 99.5% (Commercial grade carbon
dioxide from Air Liquide, 99.5% CO2, UN1013, CAS:124-38-9) was
delivered to contact the surface of the mixing concrete via a tube
of approximately 1/4'' ID whose opening was located approximately
10 cm from the surface of the mixing concrete, at a flow rate of 20
liters per minute (LPM) for 40-80 sec, for a total amount of carbon
dioxide of 13.3 L (40 sec) to 26.7 L (80 sec). The remaining water,
0.713 kg, was added to bring the mix to a w/c ratio of 0.6 while
the concrete mix continued to be mixed after the carbon dioxide
addition for approximately 2 minutes, for a total mix time of
approximately 4 minutes, with carbon dioxide addition for 40, 60,
or 80 sec during the mixing. In general, the mixing procedure was
as follows: mix dry mix and add first water addition over 15
seconds; mix for remainder of one minute; deliver CO.sub.2 while
mixing for 40, 60 or 80 seconds; when the delivery was 40 seconds
there was an additional 20 sec of post-CO.sub.2 mixing to bring the
step up to one minute, when the delivery was 60 or 80 seconds the
next step began immediately after the CO.sub.2 was stopped; add the
second water addition and mix two minutes. In one test an
additional 5% water was added. These tests were done with Shaw pre
bagged mix, which required more water and was assumed to contain
more cement (17%). The two water additions were 1.15 kg (58% giving
0.34 estimated w/c) and 0.850 kg (to give a total of 2.0 kg of
water and estimated 0.59 w/c). In the case of 5% added water it was
only applied on the second addition (1.150 kg or 55%, then 0.950 kg
for a total of 2.1 kg and estimated 0.62 w/c). Control concrete
mixes were prepared with the same final w/c ratio and mixing time,
but no addition of carbon dioxide. The mixed concrete was poured
into cylinders and strength tests were performed at 7 days. The
results are shown in FIGS. 4 and 5, where the bars represent the
data range (high to low) and the point in the middle corresponds to
the average. The concrete mixes that had been exposed to carbon
dioxide showed 7-day strengths comparable to the controls.
[0398] In a second experiment, several batches were prepared. In
each batch, approximately 20 kg of bagged readymix concrete (BOMIX
bagged readymix) was mixed with water in a Hobart mixer. The cement
content of the concrete was not known but was assumed to be 20%. A
first water addition of 0.6 kg (30% of total water) was added for a
w/c ratio of 0.15 and the mixer was topped with a loose lid. The
concrete mix was mixed for a total of 1 minute. Then a gas mixture
containing carbon dioxide at a concentration of 99.5% (Commercial
grade carbon dioxide from Air Liquide, 99.5% CO2, UN1013,
CAS:124-38-9) was delivered to contact the surface of the mixing
concrete via a tube of approximately 1/4'' ID whose opening was
located approximately 10 cm from the surface of the mixing
concrete, at various flow rates for different batches, for 60 sec,
to give different total carbon dioxide doses for different batches.
The remaining water of 1.4 kg was added to bring the mix to a w/c
ratio of 0.5 while the concrete mix continued to be mixed after the
carbon dioxide addition for approximately 2 minutes, for a total
mix time of approximately 4 minutes, with carbon dioxide addition
for 60 sec during the mixing (one minute premix, 60 sec CO.sub.2
dose, then add remainder of water and finish with two minutes
mixing for 4 minutes total). Control concrete mixes were prepared
with the same final w/c ratio and mixing time, but no addition of
carbon dioxide. The mixed concrete was poured into 5 4 kg cylinders
(100 mm diameter by 200 mm, or 4 inches by 8 inches) and strength
tests were performed at 7, 14, and 28 days. The carbon dioxide
dosage is expressed on a per-cylinder basis, and was 5, 10, 15, 20,
25, or 30 g per cylinder, depending on the batch, which was 0.6,
1.3, 1.9, 2.5, 3.1, or 3.8% carbon dioxide bwc, respectively. The
results are shown in FIGS. 6, 7, and 8. The concrete mixes that had
been exposed to carbon dioxide showed 7-day compressive strengths
comparable to the controls, with a trend toward increasing 7-day
strength with increasing carbon dioxide dose (FIG. 6). 14-day
compressive strengths were comparable to or lower than controls at
two doses, 15 and 20 g (FIG. 7). 28-day compressive strengths were
comparable to the control, with a trend toward increasing 28-day
strength with increasing carbon dioxide dose (FIG. 8).
[0399] In a third experiment, additional water was added to
compensate for reduced flowability (slump) observed in the concrete
mixes contacted with carbon dioxide in the previous experiments.
Concrete mixes were prepared as in the second experiment, except
the dosages of carbon dioxide used was 15 g per cylinder (1.9%
carbon dioxide bwc). In addition, in one set of both control and
carbon dioxide batches, the second water addition was increased to
give a total water that was 4.7% increased over the default water
addition 7-, 14-, and 28-day compressive strength tests were
conducted. The results are shown in FIG. 9. Even with the
additional water the concrete mix contacted with carbon dioxide
showed a 28-day strength comparable to control.
[0400] In a fourth experiment, various additional water amounts
were investigated. Concrete mixes were prepared as in the second
experiment, except the dosages of carbon dioxide used was 10 or 15
g per cylinder (1.3 or 1.9% carbon dioxide bwc, respectively). In
addition, in sets of both control and carbon dioxide batches, the
second water addition was increased to give a total water that was
2100, 2200, 2300, 2400, or 2500 ml/20 kg dry mix, compared to 2000
ml/kg for control batches. The amount of water on the first
addition was 60% of the total water so the w/c at time of carbon
dioxide was increased as mix water was increased. 7- and 28-day
compressive strength tests were conducted. The results are shown in
FIGS. 10-13. Slump tests were also conducted and the results are
shown in FIG. 14. Additional water partially compensated for the
decrease in slump with carbon dioxide addition, especially at the
lower carbon dioxide dose. 7 day strength was comparable to control
for most doses of water.
Example 2
[0401] This example describes retrofitting an existing readymix
truck with a system for contacting a wet concrete mix in the drum
of the truck with carbon dioxide while the concrete mix is
mixing.
[0402] A readymix concrete truck was retrofitted for delivery of
carbon dioxide to the mixing concrete mix. A flexible rubber tube
of approximately 3/4'' diameter was brought to the readymix site
and the readymix truck was retrofitted by running a flexible rubber
tubing for delivery of carbon dioxide in parallel with existing
tubing for delivery of water to allow delivery of carbon dioxide to
the drum of the truck at the high end of the drum while a hydraulic
cement mix, e.g., concrete, was mixing in the drum. The opening of
the tube was positioned 0.5 to 2 m from the concrete in the truck.
The truck was a six cubic meter transit mixer. A source of carbon
dioxide was attached to the flexible rubber tubing. In this
example, the source of carbon dioxide was a liquid carbon dioxide
supply, heater (ethylene glycol), gas buffer tank, gas metering
equipment, and gas output, to supply carbon dioxide of at least 99%
concentration. The gas delivery trailer took liquid carbon dioxide,
metered by a pressure regulator and ran it through a heat exchanger
where hot liquid glycol (antifreeze) heated it to change the liquid
carbon dioxide into a gas. The gas was stored in the receiver tanks
on a mobile cart which can be wheeled out of the trailer to a
location inside the plant. A touchscreen was used to program the
correct dose of carbon dioxide to be delivered during the concrete
making process. Valves and sensors were used to meter the gas
correctly. Hoses were used to connect between the trailer, cart and
manifolds and the manifolds attach to the concrete making machine
to deliver the gas dose in the correct location. In industrial
trials the gas line was 3/4'' diameter.
[0403] In another readymix truck retrofit, the truck was
retrofitted by connecting the carbon dioxide source to the drum
through the water line release. The water line went from the water
tank on the truck to a T junction. Going up from the T sent the
water into the drum. Going down from the T was a drain to empty the
line onto the ground. The water supply was turned off when not in
use, essentially connecting the outlet to the drum. By booking the
gas supply into the outlet, in this example, the parallel line
approach was avoided and it was only necessary to use a carbon
dioxide supply and a conduit to connect to the T junction.
Example 3
[0404] This example describes the use of carbon dioxide to contact
a mixing concrete mix in a readymix truck.
[0405] The retrofitted readymix truck described in Example 2 was
used. The components of a batch of concrete were added to the drum
of the truck, including cement mix and aggregate. While the
hydraulic cement mix was mixing, carbon dioxide in a gaseous
mixture that was at least 99% carbon dioxide was introduced into
the drum at a flow rate of 750, 1500, or 2250 liters per minute for
180 seconds, for a total carbon dioxide dose of 0.5%, 1.0%, or 1.5%
bwc, respectively. The drum remained open to the atmosphere during
the carbon dioxide addition. After the flow of carbon dioxide had
stopped, additional water was added to the mixing concrete to bring
the w/c ratio of the concrete to 0.45. The truck received the
concrete and the carbon dioxide at the batching bay, and delivered
the concrete to an adjacent building where testing was done and
samples were made. Tests were conducted for temperature, slump, and
air content, and cylinders were made for strength and flexural
strength.
[0406] In a second mixing example, carbon dioxide was added before
any additional water was added to the mix, and the water in the mix
during carbon dioxide addition was due to water in the aggregate
mix, which had been exposed to water before addition. The aggregate
was wet and with the addition of the wet aggregate the water
content of the resulting hydraulic cement mix (concrete) was a w/c
ratio of 0.17. Final mix water was achieved by adding water to the
truck manually attain desired consistency.
Example 4
[0407] This example describes retrofitting a stationary pan mixer
used to mix concrete for use in a precast concrete operation with a
system for contacting the mixing concrete in the mixer with carbon
dioxide. A gas line was attached to a carbon dioxide supply and run
to a pan mixer for mixing concrete for delivery to a mold. The line
was configured to allow a controllable flow of carbon dioxide from
the carbon dioxide to the mixer for a predetermined time during
mixing of the wet mix.
Example 5
[0408] This example describes the use of carbon dioxide to contact
a mixing concrete mix in a stationary pan mixer and pouring the
concrete into molds for precast concrete products. A retrofitted
pan mixer as described in Example 4 was used to deliver carbon
dioxide to a wet concrete mix in a mixer while the concrete was
mixing, for 3 minutes, to obtain a dose of carbon dioxide of 0.5%
to 2.5% bwc. The gas line was about 1 m from the concrete.
Example 6
[0409] This example describes the use of carbon dioxide to contact
mixing concrete mix in two different ready mix operations.
[0410] In a first operation, the following mix was used: [0411] 30
MPa with a maximum 4'' slump [0412] 20 mm aggregate--2780 kg [0413]
Sand--2412 kg [0414] Washed sand--615 kg [0415] Type 10 GU
cement--906 kg [0416] Fly ash--192 kg [0417] Visco 2100--850 ml
[0418] ViscoFlow--1650 ml [0419] Water--334 litres
[0420] The carbon dioxide was added via a 3/4'' diameter rubber
hose clipped to the side of the truck and disposed in the mixing
drum to deliver CO.sub.2 to the surface of the mixing concrete for
180 sec (controlled manually), at low, medium or high dose, to
achieve 0.43, 0.55, and 0.64% CO.sub.2 bwc, respectively. Because
the aggregate was wet, CO.sub.2 was added to the mix before the
final addition of water; the w/c of the mix when CO.sub.2 was added
was calculated to be 0.16. Final water was added immediately after
the CO.sub.2 addition.
[0421] The addition of CO.sub.2 greatly reduced slump as time from
arrival at site progressed, see FIG. 15. Carbonated concreted
showed reduced strength at 7 days compared to control, increasing
in strength over time so that by day 56 the carbonated concrete was
stronger than uncarbonated at all doses tested. See FIG. 16. The
addition of CO.sub.2 caused an increase in temperature of the wet
cement that was dose dependent, as shown in Table 2.
TABLE-US-00002 TABLE 2 Effect of CO.sub.2 dose on temperature,
ready mix Mix Temperature (.degree. C.) Control 15.2 0.43% CO.sub.2
17.0 0.55% CO.sub.2 18.4 0.64% CO.sub.2 19.4
[0422] Rapid chloride penetration tests (RCPT, using ASTM C1202
Standard Test Method for Electrical Indication of Concrete's
Ability to Resist Chloride Ion Penetration) and flexural strength
tests were also performed. See FIG. 17. Although RCPT increased
with carbonation (FIG. 17A), since the control concrete was at the
high end of low (generally considered 1000 to 2000 coulombs) and
the carbonated concrete was at the low end of moderate (generally
considered to be 2000 to 4000 coulombs) the difference was not
considered to be significant. Flexural strength decreased slightly
with carbonation (FIG. 17B).
[0423] In a second operation, mixes were prepared to meet a
pre-determined slump target of 5 inches, with additional water
added to carbonated batches as necessary to achieve target slump.
The following mix was used: [0424] Sand--770 kg/m.sup.3 [0425] 20
mm Stone--1030 kg/m.sup.3 [0426] Cement GU--281 kg/m.sup.3 [0427]
Fly Ash (F)--55 kg/m.sup.3 [0428] Water--165 L/m.sup.3 [0429]
Daracem 50--1400 ml/m.sup.3 [0430] Darex II--200 ml/m.sup.3 [0431]
Total--2301 kg [0432] Water on CO.sub.2 batches increased (unknown
amount added after CO2 injection ends) to achieve target slump.
[0433] CO.sub.2 was introduced into the mixing drum of the ready
mix truck via a hose connected at a T-junction to an existing water
line that discharged into the mixing drum. As in the previous
operation, because the aggregate was wet, CO.sub.2 was added to the
mix before the final addition of water; the w/c of the mix when
CO.sub.2 was added was calculated to be 0.16. Final water was added
immediately after the CO.sub.2 addition. Two doses of CO.sub.2 were
used, 0.5% and 1.0% bwc, as well as an uncarbonated control.
Additional water was added to the carbonated concrete to achieve
target slump. The concrete was used in a precast operation on site
and arrived 20-25 minutes after the mixing started.
[0434] The use of additional water brought the slump of the
carbonated concrete to levels comparable to the uncarbonated
control, as shown in Table 3:
TABLE-US-00003 TABLE 3 Slump, temperature, and air content of
uncarbonated and carbonated ready mix concretes Air Slump
Temperature Mix Content (in) (.degree. C.) Control 3.6% 5.5 23.9
0.5% 4.2% 4.5 26.2 CO.sub.2 1.0% 4.1% 5 28.6 CO.sub.2
[0435] For the 0.5% carbonated concrete, two later slump
measurements, at 20 min and 35 min after arrival at the job site,
were both 5 inches. Further measurements were not obtained for the
1.0% sample.
[0436] Compressive strengths of the batches are shown in FIG. 18.
The 0.5% CO.sub.2 mix showed 85% strength compared to control at 1
day, equivalent strength at 7 and 28 days, and 106% of control
strength at 56 days. The 1.0% CO.sub.2 mix showed 71% strength
compared to control, and 94% at 28 and 56 days. The additional
water added to achieve the target slump likely reduced compressive
strength of the concrete.
[0437] In a third operation, an admixture, sodium gluconate, was
used to restore flowability. The following mix was used: [0438]
Sand--770 kg/m.sup.3 [0439] 20 mm Stone--1030 kg/m.sup.3 [0440]
Cement GU--336 kg/m.sup.3 [0441] Water--163 L/m.sup.3 [0442]
Daracem 55--1350 ml/m.sup.3
[0443] CO.sub.2 was introduced into the mixing drum of the ready
mix truck via a hose connected at a T-junction to an existing water
line that discharged into the mixing drum. As in the previous
operation, because the aggregate was wet, CO.sub.2 was added to the
mix without a first water addition, and before the final addition
of water; the w/c of the mix when CO.sub.2 was added was calculated
to be 0.16. Final water was added immediately after the CO.sub.2
addition. Two doses of CO.sub.2 were used, 1.0% and 1.5% bwc, as
well as an uncarbonated control. Sodium gluconate was added to the
1.5% CO.sub.2 batch at dose of 0.05% bwc, after the addition of
CO.sub.2. The concrete was used in a precast operation on site and
arrived 20-25 minutes after the mixing started.
[0444] The use of the sodium gluconate brought the slump of the
1.0% carbonated concrete toward levels comparable to the
uncarbonated control, as shown in Table 4:
TABLE-US-00004 TABLE 4 Slump, temperature, and air content of
uncarbonated and carbonated ready mix concretes Air Slump
Temperature Mix Content (in) (.degree. C.) Control 5.9% 7 25.8 1.0%
5.9% 4 28.1 CO.sub.2 1.5% 4.5% 3 28.6 CO.sub.2
[0445] For the 1.0% carbonated concrete (with sodium gluconate), a
later slump measurements, at 20 min after arrival at the job site,
was 5.5 inches. For the 1.5% carbonated concrete (no sodium
gluconate), a later slump measurements, at 15 min after arrival at
the job site, was 3.0 inches. Carbon dioxide uptake of the 1.0%
dose was 0.44% bwc, for an efficiency of 44%. Carbon dioxide of the
1.5% dose was 1.69% bwc, or 113% efficiency.
[0446] Compressive strengths of the batches are shown in FIG. 19.
The 1.0% concrete (with sodium gluconate) had a compressive
strength of 96, 107, and 103% of control at 1, 28, and 56 days,
respectively. The 1.5% concrete (no sodium gluconate) had a
compressive strength of 98, 117, and 109% of control at 1, 28, and
56 days, respectively. The 1.5% CO2 concrete had a reduces slump
but was still usable.
[0447] This example illustrates that carbonation can reduce slump
in wet mix used in ready mix operations. Depending on the mix, the
slump may be such that remedial measures, such as use of additional
water, use of admixture, or both, are necessary; as illustrated by
this example, these measures can restore slump to acceptable levels
without major alteration in the strength of the concrete.
Example 7
[0448] This example describes the use of an admixture to modulate
compactability/strength of a dry cast concrete mix. Several
different tests were performed.
[0449] Work had identified that carbonation of fresh concrete prior
to formation reduced the mass of an industrially produced
carbonated dry mix product in certain mixes. Dry mix products are
made to a constant dimension so lower mass resulted in lower
density which can contribute to lower strength. A lab investigation
pursued novel admixtures to address the density issue. Sodium
gluconate was studied in a lab program. In conventional concrete
sugars are known to be set retarders. The work investigated its use
in conjunction with carbonated fresh concrete to see if the sodium
gluconate would act in relation to the reaction products causing
the density issue.
[0450] In a first test, the mix design was a dry mix concrete with
the following proportions [0451] 1.75 kg cement [0452] 15.05 kg SSD
(saturated surface dry) fine aggregate [0453] 7.00 kg SSD
(saturated surface dry) coarse aggregate [0454] 1.19 kg mix water
[0455] Target water was 6.05% by mass of the concrete
[0456] The admixtures used were: 1) Sodium gluconate to improve
density--it was prepared as a solution of 36.8 g of sodium
gluconate per 100 ml of water. It was dosed into the concrete as a
mass of solid sodium gluconate by weight of cement; 2) Rainbloc
80--a water repellency admixture for Concrete Masonry Units; and 3)
ProCast 150--an admixture for use in concrete masonry units. The
two commercial admixtures were dosed based upon mL/100 kg
cementitious materials as per manufacturer's specifications.
[0457] Samples were mixed according to the following procedure:
[0458] Aggregate is introduced first and mixed until homogenous.
[0459] Cement is introduced and mixed for 30 s until homogenous.
[0460] Mix water is added over 15 seconds. [0461] The concrete is
mixed for a total of 4 minutes starting from the water addition.
[0462] In the case of CO.sub.2 batches the following modified
sequence was used: [0463] 1 minute mixing all materials [0464]
Initial temperature is recorded [0465] CO.sub.2 gas is injected
over the surface of the mixing concrete at 100 LPM for required
time based on test plan. The gas is nominally retained in the bowl
by use of a cover that accommodates the movement of the mixing
mechanism. The mixing proceeds during the gas delivery. [0466]
Final temperature is recorded. [0467] Admixtures are introduced to
mix--always post carbonation [0468] Mix for additional time to
attain a total of 4 minutes mixing.
[0469] Concrete samples were formed according to the following
procedure [0470] Concrete was formed into standard 100 mm diameter
cylinder molds [0471] 3.5 kg of dry mix materials were introduced
into the molds and compacted using a specially designed pneumatic
ram which applies 95-100 psi of pressure directly under vibration
onto the cross section of the concrete mass [0472] A steel trowel
was used to remove any excess materials from the top of the mold
and level the surface of the test specimen. [0473] The mass of the
cylinder was recorded. [0474] Test specimens were set to cure in a
lime water bath, in accordance with ASTM C192
[0475] The first trial produced four concretes: 1) Control; 2)
Control with 0.05% sodium gluconate; 3) CO2; 4) CO2 with 0.05%
sodium gluconate. The cylinder unit mass (mass of a constant volume
of concrete) was understood as an estimate of product density. 6
samples were produced.
[0476] With the control density as the standard, the control with
sodium gluconate had a relative density of 98.8%, the carbonated
concrete was 94.0% and the carbonated concrete with sodium
gluconate was 93.4%. Thus, addition of 0.05% sg to control reduces
cylinder density 1.2%, application of CO.sub.2 reduces cylinder
density 6%, and addition of 0.05% sg to CO.sub.2 treated concrete
did not improve cylinder density. The dose is too low.
[0477] In a second trial, the same conditions for sample
preparation as for the first trial were used, with the following
carbonation and sodium gluconate conditions: [0478] Uncarbonated
with 0, 0.24% and 0.48% sodium gluconate [0479] CO.sub.2 for 1
minute with 0.06%, 0.12%, 0.24% and 0.48% sodium gluconate [0480]
CO.sub.2 for 2 minutes with 0.10%, 0.24%, 0.48% and 0.72% sodium
gluconate
[0481] The effects of various doses of sodium gluconate on density,
which can be considered a proxy for strength, is shown in FIG. 20.
Applying CO.sub.2 decreased the cylinder unit mass (proxy for
density). Increasing the amount of CO.sub.2 absorbed by the
concrete correspondingly increased the amounts of sodium gluconate
to offset the density shortcoming. Increasing the sodium gluconate
dose increased the density of all concretes over the range
considered. The control concrete cylinder unit mass increased 1.7%
at a dose of 0.48% sodium gluconate. For 1 min of CO.sub.2 the
sodium gluconate dosages of 0.24% and 0.48% both resulted in a
cylinder mass equivalent to the control. For 2 minutes of CO.sub.2
the cylinder mass was 99% of the control at a sodium gluconate
dosage of 0.48% and matched the control cylinder mass when the dose
reached 0.72%.
[0482] In a third trial, the same conditions for sample preparation
as for the first trial were used, with carbonation at 50 LPM for 90
seconds and the following sodium gluconate conditions: [0483]
Control [0484] CO.sub.2 with 0.24% sodium gluconate [0485] CO.sub.2
with 0.30% sodium gluconate [0486] CO.sub.2 with 0.36% sodium
gluconate [0487] CO.sub.2 with 0.42% sodium gluconate
[0488] Cylinder mass (density, assuming all cylinders are of equal
volume) was measured, and compressive strength measured at 1, 3,
and 7 days. Cylinder densities are shown in FIG. 21. Applying
CO.sub.2 decreased the cylinder unit mass (proxy for density).
Increasing the sodium gluconate dose increased the density over the
range considered. The effect plateaued somewhat at the higher doses
suggested the preferred dose is potentially in the 0.30% to 0.42%
range. Without gluconate the cylinder mass of a carbonated product
is about 7% less than the control. A gluconate dose of 0.30%
brought the mass to 3% under the control. A dose of 0.42% brought
the mass to 4% less than the control. The compressive strengths of
the sodium gluconate treated samples were comparable to those of
the control sample at doses of 0.30% and above.
[0489] In a fourth trial, the same conditions for sample
preparation as for the first trial were used. Carbonation was at 50
LPM for 90 seconds and the following sodium gluconate conditions:
[0490] Control [0491] CO.sub.2 [0492] CO.sub.2 with 0.30% sodium
gluconate [0493] CO.sub.2 with 0.42% sodium gluconate
[0494] All concretes contained Rainbloc (0.32%). It was added with
the mix water. The cylinder unit mass (mass of a constant volume)
was measured as a test of product density. 6 samples were produced.
The strength was measured at 1, 3 and 7 days. Cylinder densities
are shown in FIG. 22. The application of CO.sub.2 reduced the
density (by 6%) and strength of the concrete product The use of
sodium gluconate improved the density and strength. 0.3% sodium
gluconate was sufficient to make carbonated concrete with 98.5% of
the density of the control and equivalent strength. 0.42% sodium
gluconate produced carbonated concrete with equivalent density and
strength to the control. The optimum dose for this combination of
cement and mix design proportions appears to be on the order of
0.42% sodium gluconate by weight of cement.
[0495] In a fourth trial, the same conditions for sample
preparation as for the first trial were used. Carbonation was at 50
LPM for 90 seconds and the following sodium gluconate conditions:
[0496] Control [0497] CO.sub.2 [0498] CO.sub.2 with 0.30% sodium
gluconate [0499] CO.sub.2 with 0.42% sodium gluconate [0500]
CO.sub.2 with 0.30% sodium gluconate with post-CO2 addition of
Procast.
[0501] In contrast to the previous days the cement was a 70/30
blend of white cement and OPC. All batches contained Rainbloc
(0.32%) and Procast 150 (0.64%). The Rainbloc was added with the
mix water while the Procast 150 was tried both as part of the mix
water and as an addition after the carbon dioxide treatment. The
strength was measured at 1 (2 samples), and 7 days (4 samples).
Cylinder densities are shown in FIG. 23. The carbonation treatment
produced a compacted concrete product that was 7% less dense than
the control. The density was improved by adding sodium gluconate. A
dose of 0.30% sodium gluconate improved the density to 97% of the
control. A further increase to 0.42% produced a concrete product
with a density of 96%. As compared to the earlier trial that did
not include Procast, it is clear that the optimum dosage is
sensitive to the presence of other admixtures. Adding the Procast
after the carbon dioxide treatment provided improved product
density. The timing of the addition of admixtures with respect to
the carbon dioxide application is important.
[0502] This example illustrates that an admixture, sodium
gluconate, can return density and compressive strength of
carbonated dry mix samples to those of uncarbonated samples, that
the effect is dose-dependent, and that the timing of delivery of
additional admixtures added to the mix can affect strength
development.
Example 8
[0503] This example illustrates the effects of various admixtures
on the workability of carbonated mortar mix, prepared as for a wet
cast operation.
[0504] A mortar mix was prepared containing 535 g Portland cement
(Holcim GU), 1350 g sand, and 267.5 g water. CO.sub.2 gas was
introduced at 20 LPM while mixing. The time of CO.sub.2 delivery
depended on the target CO.sub.2 uptake, for example, to achieve
1.1% bwc the delivery took 3 to 4.5 min.
[0505] Three admixtures were used: sodium gluconate, fructose,
sodium glucoheptonate. The admixtures were added to carbonated
mortar at dosages of 0.05, 0.10 and 0.20% by weight of cement. The
dosages reflect solid mass of additive delivered in a solution. The
mortars were carbonated while mixing to an uptake of about 1.9% by
weight of cement. The admixture was added after the carbonation:
after carbonation the temperature of the sample was measured, then
the admixture was added and the sample was remixed to
homogenize.
[0506] The slump of the produced mortar was measured as an
assessment of workability. Slump was measure immediately after the
end of mixing using a Cement & Mortar Testing Equipments
Transparence Acrylic Mini Slump Cone Test Apparatus (NL SCIENTIFIC
INSTRUMENTS SDN. BHD. Malaysia.). Samples were rodded in two
lifts.
[0507] Carbonation greatly decreased the mortar slump, while each
of the admixtures, added after carbonation, improved slump. The
carbonated slump matched the control upon addition of 0.05%
fructose, 0.10% sodium gluconate or 0.2% sodium glucoheptonate. See
FIG. 24.
[0508] In a second test, mortar mixes were prepared and carbonated
as above, and either fructose or sodium gluconate was added before
(Pre), during (Mid), or after (Post) carbonation, and the CO.sub.2
uptake as well as slump was measured in the mortar mix. It was seen
that the addition of admixture either Pre or Mid carbonation did
not appreciably correct the decrease in slump caused by
carbonation, whereas the addition of admixture Post carbonation
greatly improved the slump (the apparent improvement in slump in
the sodium gluconate Pre sample can be attributed to the
anomalously low carbon dioxide uptake of this sample); this was
true for both sodium gluconate and fructose. See FIG. 25.
Example 9
[0509] This example illustrates the effect of the time of addition
of admix on workability and strength development in a carbonated
mortar mix, as for a wet cast operation.
[0510] In a first test, mortar mix was prepared containing 535 g
Portland cement (Holcim GU), 1350 g sand, and 267.5 g water.
CO.sub.2 gas was introduced at 20 LPM while mixing. The time of
CO.sub.2 delivery depended on the target CO.sub.2 uptake, for
example, to achieve 1.1% bwc the delivery took 3 to 4.5 min. Mortar
cubes were created with C109M-12 Standard Test Method for
Compressive Strength of Hydraulic Cement Mortars. All samples
contained 0.10% bwc PCE (Mighty 21ES by Kao Chemicals) to assist
casting of cubes.
[0511] Sodium gluconate was added either before or after
carbonation, at 0, 0.025, 0.05, and 0.075% bwc. Compressive
strength at 24 hours was measured at 24 hours and compared to
uncarbonated control. See FIG. 26. The sodium gluconate added after
carbonation did not affect the 24-hour compressive strength,
whereas sodium gluconate added before carbonation improved 24-hour
compressive strength, but the mix was found to be stiff. The mix
with sodium gluconate added after carbonation was workable, but
strength development was adversely impacted.
[0512] In a second test, mortar was prepared and carbonated with or
without sodium gluconate, added before or after carbonation, as in
the first test, except the cement was Lehigh cement. The results
were similar to those for mortar prepared with Holcim cement: When
added after CO.sub.2 the admix was a retarder and resulted in lower
strengths at 24 hours. When added before the CO.sub.2 the retarding
effect was not evident and 24 h strength was .about.90% of control
with relatively small SG dosages.
Example 10
[0513] This Example illustrates the effects of system temperature
on carbon dioxide uptake in a wet mix.
[0514] In a first test, an experiment was conducted to look at the
effect of the initial temperature of the materials on the
carbonation behavior of fresh cement paste. Three target starting
temperatures were considered, 7.degree. C., 15.degree. C. and
25.degree. C. (actual temperatures were .+-.2.degree. C.).
Measurements include the mortar temperature, mini-slump (vertical
slump and lateral spread), carbon dioxide uptake, and cube
strength.
[0515] A mortar mix was prepared containing 535 g Portland cement
(Holcim GU), 1350 g sand, and 267.5 g water. The mix was brought to
7, 15, or 25.degree. C., and CO.sub.2 gas was introduced at 20 LPM
while mixing. The time of CO.sub.2 delivery depended on the target
CO.sub.2 uptake, for example, to achieve 1.1% bwc the delivery took
3 to 4.5 min. CO.sub.2 uptake at various time points was measured.
Slump measurements were also taken at various time points.
[0516] The effect of temperature on rate of carbon dioxide uptake
is shown in FIG. 27, where the upper line and points are for
25.degree. C., the middle line and points are for 15.degree. C.,
and the lower line and points are for 7.degree. C. Rate of uptake
of carbon dioxide increased as temperature increased; the rate was
0.087% bwc/min at 7.degree. C., 0.231 bwc/min at 15.degree. C., and
0.331 bwc/min at 25.degree. C. The rate of carbon dioxide uptake
increased 278% as temperature increased from 7 to 25.degree. C.
[0517] The effect of temperature on slump is shown in FIG. 43.
There was little effect on the workability with uptake of the
mortar prepared at 7.degree. C. (upper line and points). The
workability of the mortar prepared at 15.degree. C. declined
rapidly with increasing uptake (lower line and points). The
workability of the mortar prepared at 25.degree. C. was between
that of the two other mortars declining with uptake but taking
higher uptakes than the 15.degree. C. sample to reach zero
workability (middle line and points).
[0518] In a second experiment, the effect of carbon dioxide
temperature (heated or unheated (cold) or form (dry ice), in some
cases combined with the use of ice water, on carbon dioxide uptake
was measured in a cement paste system. Cement, mix water (untreated
or ice water) and admix were mixed for 30 seconds in blender, and
initial properties and temperature of the paste were evaluated. The
paste was then carbonated while mixing in the blender. Carbonate
while mixing in the blender, using heated gas, unheated gas (cold
gas), or dry ice. Evaluate the final properties and temperature of
the paste. FIG. 28 shows the results of the study. Heated or cold
gases seemed to give approximately equivalent uptake. The mixes
with cold temperature (cold mix water, dry ice) did not give
improved carbon dioxide uptake.
Example 11
[0519] This example illustrates the beneficial effect of calcium
containing compounds added before carbonation on 24 hour strength
development in a carbonated mortar mix.
[0520] A mortar mix was prepared containing 535 g Portland cement
(Holcim GU), 1350 g sand, and 267.5 g water. CO.sub.2 gas was
introduced at 20 LPM while mixing. The time of CO2 delivery
depended on the target CO.sub.2 uptake, for example, to achieve
1.1% bwc the delivery took 3 to 4.5 min. Mortar cubes were created
with C109M-12 Standard Test Method for Compressive Strength of
Hydraulic Cement Mortars. A plasticizer (0.10% Mighty ES+0.10% Sika
VF) with or without Ca(OH).sub.2 (2.0% bwc) was added before
carbonation, and effects on 24-hour compressive strength were
measured. The results are shown in FIG. 29. Carbonation decreased
the 24 hour strength of the mortar. The use of a plasticizer
improved the strength of both carbonated and control mortars. The
further addition of Ca(OH).sub.2 decreased the 24 hour strength of
the control product but further increased the 24-hour strength of
the carbonated product.
[0521] In a second experiment, CaO (1.5%), NaOH (2.2%),
Ca(NO.sub.2).sub.2, or CaCl.sub.2 (3.0%) were added before
carbonation to a mortar mix as above. Results are shown in FIG. 30.
All calcium compounds showed benefits for strength development in
the carbonated mortar mix, relative to carbonated mortar mix with
no admixture added.
Example 12
[0522] This example illustrates that the timing of addition of an
admixture used for conventional purposes, in this case an air
entrainer, relative to carbonation, may be important to retain the
effect of the admixture.
[0523] A calcium hydroxide slurry was used as a test system. 20 g
of Ca(OH).sub.2 was mixed with 40 g water to form a slurry.
CO.sub.2 gas was injected into the slurry at 5 LPM. The
temperature, an indicator of carbon dioxide uptake, was measured
over a 9-minute period. The plain slurry contained no admixture,
while the slurry with an air entrainer contained 2.5% (by mass of
Ca(OH).sub.2 of a liquid solution of hydrocarbons used for air
entrainment in concrete (AirEx-L, Euclid Chemical). The carbon
content was quantified using a combustion infrared detection carbon
analyzer (Eltra CS 800, Eltra GmbH, Germany). The net % CO.sub.2
increase was calculated in comparison to a base uncarbonated system
containing the components.
[0524] After 10 minutes of carbonation, the slurry without an
additive showed a CO.sub.2 uptake that was 25.5% of the original
solid mass, while the slurry with the air entrainer additive had an
uptake that was 36.2%; thus, the surfactant admixture increased the
CO.sub.2 uptake by 42.1%.
[0525] In a second test, various surfactants were tested for their
effects on CO.sub.2 uptake. Standard mortar mix, as in Example 8,
was used, and the surfactants were dosed at 0.10% bwc. CO.sub.2 as
injected for 6 minutes during mixing. Initial and final
temperatures were measured and net increase in CO.sub.2 content was
measured as above. The results are shown in Table 5.
TABLE-US-00005 TABLE 5 Effects of surfactants on CO2 uptake Initial
Final Net Temp, Temp, Temp CO.sub.2 CO.sub.2 Additive Source
.degree. C. .degree. C. Change % increase None 23.8 33 9.2 1.65
Baseline Sunlight Dish soap 24.1 41.4 17.3 2.89 75% Sunlight Dish
soap 24.1 41.9 17.8 3.34 102% MB AE-90 BASF 23.4 33 9.6 1.80 9%
Solar: w Guelph 23.8 35.2 11.4 2.17 31% Soap AirEX-L Euclid 23.8
40.6 16.8 2.84 72%
[0526] In a third test, mortar batches as above, containing 0.1%
bwc of a surfactant air entrainer (Euclid AirEx-L), or no
surfactant (control) were exposed to CO.sub.2 during mixing for 0,
2, 4, or 6 minutes, and the CO.sub.2 uptake measured. There was
greater uptake in the mortar treated with air entrainer than in
control, untreated mortar at all time points, but the relative
improvement was greater at the low exposure times: there was a 117%
increase in CO.sub.2 uptake compared to control at 2 min, a 104%
increase in CO.sub.2 uptake at 4 minutes, and a 28% increase in
CO.sub.2 uptake at 6 min.
[0527] In a fourth test, the effect of CO.sub.2 addition before or
after addition of an air entrainer on mortar density was tested. A
lower unit weight indicated a higher air content. Four air
entrainers were used: Euclid Air-Ex-L, Grace Darex ii, BASF MB-AE
90, and Grace Darex AEA ED. The results are shown in FIG. 31. In
all cases, addition of the air entrainer pre-CO.sub.2 treatment led
to an increase in density, whereas addition of the air entrainer
post-CO.sub.2 treatment resulted in a density the same as untreated
mortar.
[0528] This Example illustrates that the timing of CO.sub.2
treatment relative to addition an air entrainer affects rate of
CO.sub.2 uptake and density. If it is desired to maintain the
density effect of the air entrainer, it should be added after
CO.sub.2 addition. In some cases, a two-dose approach could be used
where an early dose of air entrainer is used to enhance CO.sub.2
uptake, then a later dose to achieve desired effects on
density.
Example 13
[0529] This Example describes tests of carbonation in a precast dry
mix operation. Tests were conducted at a precast facility in which
a concrete mix was carbonated at different stages of the casting
process, in some cases using a sodium gluconate admixture at
various concentrations. The effects of carbonation, with and
without admixture, on strength and water absorption were
measured.
[0530] The concrete mix shown in Table 6 was used.
TABLE-US-00006 TABLE 6 Standard Block Design Component Name Amount
Coarse aggregate Birdseye Gravel 685 lb Fine aggregate Meyers Mat
Torp Sand 4320 lb Fine aggregate Silica Sand/Wedron 430 1250 lb
Cement Illinois Product 1000 lb Admixture Rainbloc 80 .sup. 50 oz
Target water content 6.5%
[0531] The aggregates, cement and water were added to a planetary
mixer. Carbon dioxide was flowed into the mixer via a 3/4 inch
diameter rubber pipe for 180 s at a flow rate to achieve the
desired carbonation. In some runs, carbon dioxide was added both at
the mixer and at the feedbox. In a preliminary run, all water was
added initially, but in subsequent runs, additional water was added
about halfway through the 180 s according to an assessment of the
mix consistency prior to the completion of the mix and additional
water was added as necessary to achieve a desired mix look. Batches
with carbon dioxide delivered to the concrete required additional
water nearly in proportion to the amount of carbon dioxide gas
supplied. The concrete mix was placed in a mold to produce 8 inch
blocks, which were tested for density, compressive strength at 7,
28, and 56 days, and water absorption (all according to ASTM C140,
5 blocks per test). The carbonation of the concrete was also
determined: The samples for analyzing the carbon dioxide content of
the concrete were created by taking a fresh sample from the
production line, drying the concrete on a hot plate to remove the
water, and subsequently sieving the material through a 160 .mu.m
sieve. Samples of the raw materials were examined to determine how
much of each component passes a 160 .mu.m sieve and the carbon
content of the passing material. This information, along with the
concrete mix design, allows for the calculation of a theoretical
control carbon content against which analyzed samples can be
compared. The carbon content was quantified using a combustion
infrared detection carbon analyzer. The net % CO.sub.2 increase was
calculated in comparison to a base uncarbonated system containing
the components.
[0532] In a first test, carbonation at both the feedbox and mixer
or just the feedbox was tested. The variations examined are
summarized in TABLE 7, below. Data for controls, which were
prepared on other days (samples 500 and 700), are also
presented.
TABLE-US-00007 TABLE 7 Standard Block Production Variables and
Water Contents Total Dose Water Code Condition Mode (% bwc) w/c
fraction 0600 Control Uncarbonated -- 0.392 6.64% 0601 CO.sub.2
Feedbox 0.5% 0.5% 0.422 8.32% 0602 CO.sub.2 Mixer 0.5% 0.5% 0.430
8.25% 0603 CO.sub.2 Mixer 1.0% 1.0% 0.440 8.08% 0604 CO.sub.2 Mixer
1.0%, Feedbox 1.5% 0.450 8.23% 0.5% 0605 CO.sub.2 Mixer 1.5% 1.5%
0.455 8.39% 0500 Control Uncarbonated -- 0.406 8.88% 0700 Control
Uncarbonated -- 0.426 7.45%
[0533] FIG. 32 shows the results of tests for carbon dioxide
uptake, compressive strength, water absorption, and density for the
blocks produced in this test.
[0534] The efficiency of carbon dioxide uptake was greatest in the
1.5% bwc dose where carbon dioxide was delivered only to the mixer
(batch 0605); delivery of 0.5% of the dose at the feedbox was
consistently less efficient than delivery of all of the same dose
at the mixer (batch 0601 compared to batch 0602; batch 0604
compared to batch 0605). A carbon dioxide uptake efficiency of 93%
was achieved with a CO.sub.2 dose of 1.5% delivered solely at the
mixer (batch 0605). Consequently, in subsequent tests a dose of
1.5% CO.sub.2, delivered solely at the mixer, was used.
[0535] The addition of CO.sub.2 to the mix consistently improved
compressive strength at 7, 28, and 56 days, at all doses tested,
whether or not the CO.sub.2 was added at the mixer, the feedbox, or
both. The overall average compressive strengths of the two
(uncarbonated) control sets (0500 and 0700) were 2843, 3199, and
3671 psi at 7, 28, and 56 days, respectively. At 7 days the first
four batches made with CO.sub.2 (0601, 0602, 0603, and 0604) showed
a 30-36% strength benefit over the average control, and the final
carbonated batch (0605) was 18% stronger. The strength benefit was
maintained at 28 days with a benefit of the first four carbonated
conditions ranging from 29037% and the final batch being 19% better
than the average control. The 56 day results indicated the strength
benefit had increased to 30-45% for the first four sets and 36% for
the final set.
[0536] Water absorption was reduced through carbonation. Mixes 0601
to 0603 had a water absorption about 35% lower than that of
uncarbonated control (0500 and 0700), and mixes 0604 and 0605, in
which 1.5% CO.sub.2 was added, had a water absorption of about 18%
lower than control.
[0537] Density of the carbonated mixes varied with amount of carbon
dioxide added. The density of the two lowest CO.sub.2 (0.5%)
batches (0601 and 0602) was about 2.5% higher than control, but the
density of the batches carbonated at a dose of 1.0 or 1.5% (0603,
0604, and 0605) were equivalent to the density of the control.
[0538] Overall, this test indicated that carbonation of this
mixture in a precast operation producing 8 inch blocks indicated
that an efficiency of carbon dioxide uptake of over 90% could be
achieved, producing blocks that were stronger than uncarbonated at
all carbon dioxide doses and time points tested, culminating in a
56 day strength that averaged over 30% greater than control. Water
absorption of the carbonated blocks was consistently lower than
control, and the blocks carbonated at 1.0 and 1.5% CO.sub.2 dose
had a density the equivalent of uncarbonated blocks.
[0539] In a second test, the mix of TABLE 8 was used, with a dose
of 1.5% CO.sub.2, delivered at the mixer, and, in addition five
different doses of a sodium gluconate admixture were delivered-0.1,
0.2, 0.3, 0.4, and 0.5% bwc. The sodium gluconate was delivered in
water solution, dissolved one gallon of water (0.1, 0.2, and 0.3%)
or in two gallons of water (0.4 and 0.5%). The sodium gluconate
admixture was added about 75 s after carbon dioxide delivery to the
mixer started, and took about 90 s to add. Admixture was added
manually during the mixing cycle. The addition of admixture was
begun during the carbon dioxide addition so as not to extend the
mixing cycle. Carbonation, compressive strength, density, and water
absorption were measured.
[0540] The investigated variables and water contents are summarized
in Table 8. The overall results are summarized in FIG. 32.
TABLE-US-00008 TABLE 8 Standard Block, with sodium gluconate
CO.sub.2 Dose Sodium Water Code Condition Mode (% bwc) gluconate
w/c fraction 0700 Control -- -- -- 0.425 7.35% 0701 CO.sub.2 Mixer
1.5 0.5% 0.413 8.12% 0702 CO.sub.2 Mixer 1.5 0.4% 0.413 7.85% 0703
CO.sub.2 Mixer 1.5 0.3% 0.424 7.99% 0704 CO.sub.2 Mixer 1.5 0.2%
0.426 7.87% 0705 CO.sub.2 Mixer 1.5 0.1% 0.433 7.81% 0706 Control
-- -- -- 0.426 7.45%
[0541] The efficiency of CO.sub.2 delivery for batches produced in
this test was found to range from 78% to 94%, across all batches.
The gas injection parameters were held constant and the average
efficiency was found to be about 85%.
[0542] It was shown that the strength was sensitive to the admix
dose. See FIG. 33. The control strength can be taken at 100% at all
ages and the carbonated strengths are shown in relative comparison.
For the lower doses the carbonated concrete strength was equivalent
to the control strength at both 7 and 28 days. For a dose of 0.4%
there was a 12% strength benefit at 7 days and equivalent
performance at 28 and 56 days. For a dose of 0.5% there was a 34%
strength benefit at 7 days, 28% at 28 days, and 25% at 56 days.
These results indicate that there is a certain amount of admixture
required in the concrete beyond which a strength benefit can be
realized.
[0543] It is shown that the water absorption was again reduced for
the carbonated products. All carbonated mixes were dosed with 1.5%
CO.sub.2 bwc and had similar uptakes. The water absorption was
reduced 12% for the lowest and 31% for the highest admixture dose.
The density showed some dependence on admixture dosage. The
carbonation treatment with the small dose of admixture decreased
the density from 131 to 128.5 lb/ft.sup.3 (though it can be noted
that the strength remained equivalent to the control). The density
increased with admixture dose and equivalent density was found with
a dose of 0.3% and density was 1.3% higher for the highest admix
dose.
[0544] Emissions reduction: The carbon dioxide absorbed in the
concrete can effectively reduce the embodied carbon emissions. If
the block mass and mix design are known, then the total emissions
related to the cement can be determined. In this Example, the 17.7
kg block is found to be 12.9% (by wet mass) cement and thus there
are 2282 g of cement in each block. The cement was suggested by the
supplier to be 94% clinker. If the emissions intensity of the
clinker is assumed to be a generic 866 kg CO.sub.2e/tonne of
clinker produced then the clinker emissions for each block reach
1858 g. A generic carbonation uptake scenario can allow for an
overall carbon dioxide absorption and net emissions offset to be
calculated. The overall uptake efficiency in the present Example,
taking into account all testing, was 88%. A 1.5% dose by weight of
cement means that 34.2 g of CO.sub.2 are dosed per block while the
uptake efficiency means that 30.1 g are bound as stable carbonate
reaction products in the block. The difference is a loss
representing the 12% inefficiency. Under these assumptions, the
absorbed amount of carbon dioxide represents a direct offset of
about 1.62% of the emissions from the clinker production. A net
sequestration consideration requires a detailed analysis including
the emissions required to implement the technology. A reasonable
estimate can be made by considering the energy to capture and
compress the CO.sub.2 and the distance the CO.sub.2 had to be
transported. Additional factors are relevant (such as the creation
and transport of the hardware for the technology) but are
considered minor in the face of the gas-related aspects. The
closest industrial CO.sub.2 source to the trial site was 63 miles
away. The transportation emissions can be taken to be 222 g
CO.sub.2/tonne-mile of freight (United States Environmental
Protection Agency, 2014). The energy required to capture carbon
dioxide is on the order of 150 kWh/tonne. For 1000 blocks a 1.5%
bwc dose would inject 34,250 g of CO.sub.2. The total absorption
would be 30,140 g of CO.sub.2. The gas processing and transport is
calculated with respect to the total injected amount. The carbon
dioxide emissions associated with the energy required to capture
and compress the CO.sub.2 is 3,522 g. The transportation of the
liquid CO.sub.2 63 miles resulted in carbon dioxide emissions of
479 g. No energy is required to vaporize the liquid CO.sub.2 at the
concrete plant if an atmospheric vaporizer is employed. The
technology to carbonate 1000 blocks would result in CO.sub.2
emissions of 4,001 g. The net utilization, 26,139 g, is then the
difference between the total carbon dioxide absorbed and total
process emissions. This means that 13.3% of the absorbed carbon
dioxide cannot be associated with an environmental benefit due to
the associated emissions. However, it suggests that the net
efficacy of the CO.sub.2 utilization is 86.7%. A sensitivity
analysis can suggest how location-specific inputs can affect the
sequestration efficacy. Certain locations are further from sources
of industrial CO.sub.2 than the present case. If the liquid
CO.sub.2 transport distance was increased to 600 miles (reasonable
in markets where industrial gases are shipped from distant areas)
then the increase in transport emissions reduces the estimated
efficacy to 73.2%. However, if the distance was kept at 63 miles
then the effect of grid emissions on carbon dioxide processing
emissions can be examined. An example of low grid emissions can be
found in New York where parts of the state see 548.37 lb CO.sub.2e
/MWh (248.7 g CO2e /kWh). The reduced gas processing emissions
would increase the sequestration efficacy to 94.2%. An example of
very low grid emissions can be found in Quebec at 5.1 lb CO.sub.2e
/MWh (2.3 g CO.sub.2e /kWh), where the efficacy would reach 98.4%.
On the other hand, Colorado has high grid emissions of 1906.27 lb
CO.sub.2e /MWh (864.7 g CO.sub.2e /kWh). The efficacy would
decrease to 83.7%. These estimates are consistent with a previously
examined case. On the order of 80-90% of the carbon dioxide
absorbed by the concrete would represent a net removal of CO.sub.2
from the atmosphere while the balance would be offset by the
emissions required to employ the technology.
[0545] This example illustrates that carbon dioxide can be added to
a precast concrete mix in a dry cast operation at the mixer stage
and the products formed are generally stronger, show lower water
absorption, and equivalent density when compared to non-carbonated
products. The addition of a sodium gluconate admixture resulted in
a dose-dependent effect on strength, water absorption and density,
and indicated that an optimum dose for admixture can be achieved to
optimize these parameters.
Example 14
[0546] In this example the same precast equipment was used in the
same facility as in Example 13, but using three different concrete
mixes: a limestone mix, a lightweight mix, and a sandstone mix.
This example illustrates the importance of adjusting carbonation
mix parameters to mixes with different characteristics.
[0547] Three different mix designs were used, shown in TABLES 9,
10, and 11.
TABLE-US-00009 TABLE 9 Limestone Block Mix Design Component Name
Amount Coarse aggregate Sycamore FA-5 3152 lb Coarse aggregate
Sycamore FM-20 5145 lb Fine aggregate Silica Sand/Wedron 430 745 lb
Cement Illinois Product 351 lb Cement White Cement 819 lb Admixture
Rainbloc 80 .sup. 59 oz Admixture Frocast 150 .sup. 117 oz Target
water content 8.6%
TABLE-US-00010 TABLE 10 Lightweight Block Mix Design Component Name
Amount Coarse aggregate Birdseye Gravel 1030 lb Coarse aggregate
Gravelite 1500 lb Fine aggregate Screening Sand 2200 lb Fine
aggregate Meyers Mat Torp Sand 1500 lb Cement Illinois Product 725
lb Admixture Rainbloc 80 .sup. 34 oz Target water content 7.9%
TABLE-US-00011 TABLE 11 Sandstone Block Mix Design Component Name
Amount Coarse aggregate Sycamore FA-20 3750 lb Fine aggregate
Meyers Mat Torp Sand 1800 lb Cement Illinois Product 730 lb
Admixture Rainbloc 80 .sup. 37 oz Target water content 7.0%
[0548] Limestone Mix Test.
[0549] In a first test, the limestone mix of TABLE 9 was used.
Conditions were as for the second test of Example 13, with CO.sub.2
added at a dose of 1.5% in the mixer. Addition of 0.4% sodium
gluconate was tested. The addition of the Procast admixture that is
normally part of the mixing sequence for the limestone mix design
was delayed to be added after the carbon dioxide injection was
complete. The investigated variables and water contents are
summarized in Table 12. The overall results are summarized in FIG.
34.
TABLE-US-00012 TABLE 12 Limestone Mix Production Variables and
Water Contents CO.sub.2 Dose Water Code Mix Design Condition Mode
(% bwc) Admix w/c fraction 0805 Limestone Control -- -- -- 0.225
7.75% 0806 Limestone CO.sub.2 Mixer 1.5 0.4% 0.514 8.53%
[0550] The limestone mix design was examined in only a limited
production run partly due to the perceived difficulty of accurately
assessing the net amount of absorbed carbon dioxide against the
high carbon content of the limestone background, at least when
using the current analytical methods and procedures.
[0551] The compressive strength data showed that the carbonated
limestone blocks averaged 2349 psi at 7 days and were slightly
weaker (7%) than the control blocks. The 28 day strength was 2518
psi and 14% lower than the control. The 56 day strength averaged
2762 psi and 9% weaker than the control though this gap could be
narrowed to 6% if an outlier point was removed. The dose of
admixture in this test was determined using the Illinois Product
cement and no advance tests on the Federal White cement used in the
limestone mix design were performed. Subsequent lab development has
made it clear that the effect and dosage of the admixture is
sensitive to cement type. The integration of the carbonation
technology may require a small investigative series of trial runs
to determine both if the admixture is desired and what the proper
dose should be. The success at demonstrating the admixture usage,
for the Illinois Product cement, in the lab prior to the pilot
suggests that preliminary optimization screening could be
accomplished for any mix for which the materials were
available.
[0552] In terms of water absorption, it was found that the
carbonated limestone block had a higher absorption and lower
density than the control blocks. The absorption was increased 18%
and the density was decreased 2%. The results agree with the lower
strength of the carbonated limestone blocks and support the need to
fine tune the inputs used when carbonating this mix.
[0553] Lightweight Mix Test.
[0554] In a second test, the lightweight mix of Table 10 was
used.
[0555] Conditions were as for the second test of Example 13, with
CO.sub.2 added at a dose of 1.5% in the mixer. Addition of sodium
gluconate at three different levels, 0.35, 0.4, and 0.45% was
tested. The investigated variables and water contents are
summarized in Table 13. The overall results are summarized in FIG.
35.
TABLE-US-00013 TABLE 13 Lightweight Mix Design Production Variables
and Water Contents CO.sub.2 Dose Water Code Mix Design Condition
Mode (% bwc) Admix w/c fraction 0801 Lightweight Control -- -- --
0.745 6.96% 0901 Lightweight CO.sub.2 Mixer 1.5 -- 0.691 12.25%
0902 Lightweight CO.sub.2 Mixer 1.5 0.35% 0.703 13.79% 0802
Lightweight CO.sub.2 Mixer 1.5 0.40% 0.758 8.80% 0903 Lightweight
CO.sub.2 Mixer 1.5 0.45% 0.707 13.99%
[0556] Preliminary results suggest that an increase in CO.sub.2
content similar to what has been observed for the Standard Block
occurred for carbonated Lightweight mixes in all cases. However,
due to inherent difficulties performing carbon quantification for
these mix designs a definitive analysis was not performed, and
actual numbers obtained, in some cases over 100%, are not
reliable.
[0557] The compressive strength data for the lightweight mix is
summarized in FIG. 36. The testing broke three blocks from the
control set and five blocks from each of the carbonated sets. The
control (uncarbonated, no sodium gluconate) strength can be taken
at 100% at all ages and the carbonated (with and without sodium
gluconate) strengths are shown in relative comparison. The
carbonated batch with no sodium gluconate was slightly behind the
control at 7 days but developed strength at a faster rate
thereafter. The admixture batches were found to be stronger at the
first measurement and maintained at least this level or benefit
through the remainder of the test program.
[0558] The lightweight block production found an optimal or
near-optimal amount of admixture. With no admixture used the
strength was 11% behind the control strength at 7 days, 5% ahead at
28 days and 10% ahead at 56 days. The carbonated concrete with low
admixture dose was 22%, 42% and 41% stronger than the uncarbonated
control at 7, 28 and 56 days respectively. The 0.40% dose produced
concrete that was 76%, 94% and 84% stronger at the three ages while
the 0.45% dose of admixture resulted in 21%, 32% and 33%
improvements. These results are different than those for Standard
Block in Example 13, where an optimal dose of sodium gluconate was
not necessarily reached even at 0.5%, and illustrates the
usefulness of pre-testing, or otherwise optimizing, admixture dose
and other conditions specific to a specific mix design. See Example
15 for a further testing of this.
[0559] CO.sub.2 injection had little effect on the lightweight
block density or water absorption when no sodium gluconate was
used. Across the dosages of admixture the water absorptions were
decreased about 10% for the 0.35% and 0.45% doses and 34% for the
middle dose of 0.4%, compared to uncarbonated control without
sodium gluconate. Conversely, the density increased when sodium
gluconate was used. It was up 1-2% for high and low doses and 7%
higher for the middle dose, compared to uncarbonated control
without sodium gluconate. While the middle dose carbonated blocks
were the strongest and had the lowest water absorption they were
also the highest density. Promising strength and absorption results
were found with the other two admixture dosages and accompanied by
a small density increase. Admixture usage will generally benefit
from pre-testing or other predictive work to optimize conditions to
obtain the desired result, e.g., in the case of lightweight blocks,
a combination of strength, density, water absorption, and other
properties as desired.
[0560] Sandstone Mix Test.
[0561] In a third test, the sandstone mix of Table 11 was used.
Conditions were as for the second test of Example 13, with CO.sub.2
added at a dose of 1.5% in the mixture Addition of 0.35, 0.4, and
0.45% sodium gluconate was tested. The investigated variables and
water contents are summarized in Table 14. The overall results are
summarized in FIG. 37.
TABLE-US-00014 TABLE 14 Sandstone Mix Design Production Variables
and Water Contents CO.sub.2 Dose Water Code Mix Design Condition
Mode (% bwc) Admix w/c fraction 0803 Sandstone Control -- -- --
0.672 6.55% 0904 Sandstone CO.sub.2 Mixer 1.5 -- 0.697 6.93% 0905
Sandstone CO.sub.2 Mixer 1.5 0.35% 0.736 7.00% 0804 Sandstone
CO.sub.2 Mixer 1.5 0.40% 0.710 7.29% 0906 Sandstone CO.sub.2 Mixer
1.5 0.45% 0.718 7.02%
[0562] Preliminary analysis of the Sandstone samples found CO.sub.2
contents to be higher in all carbonated mixes relative to the
control. The average efficiency of CO.sub.2 delivery for batches
produced was found to range from 20% to 90% at a 1.5% by weight of
cement CO.sub.2 dose. From the preliminary analysis batch 0905
appears to contain a smaller amount of captured CO.sub.2 compared
to other batches produced under similar conditions. Further
analysis is currently underway to confirm this result. The average
efficiency of CO.sub.2 delivery considering all Sandstone batches
is approximately 66%, however rises to approximately 81% if batch
0905 is omitted from the calculation.
[0563] The compressive strength data for the sandstone mix is
summarized in FIG. 38. The testing broke three control blocks and
five carbonated blocks. The data is plotted to show every
individual break with the average compressive strength highlighted.
The sandstone carbonated blocks with no admixture had a strength
that was functionally equivalent to the control (carbonated, no
admixture) strength (4% behind at 7 days, 2% ahead at 28 days and
5% behind at 56 days). Of three doses of admixture, strength
increased with admixture dosage suggesting that the dosage was
reaching an optimum across the range considered. The 7 day strength
benefit was 7%, 9% and 63% on the three admixture dosages
considered. The benefit at 28 days was 8%, 22% and 63%
respectively. At 56 days was 9%, 8% and 58% respectively. The
strength increase with admixture dose across the range of dosages
mirrors the data with the Standard Block of Example 13 wherein some
"threshold" amount of admix seems to be crossed in relation to the
amount of carbon dioxide present in the concrete.
[0564] The carbonation treatment without using the admixture
increased the water absorption 12% and decreased the density 3%.
The use of admixture brought the metrics back in line with the
control at the lowest dose and offered significant improvement at
the highest dose. The water absorption was reduced 19% and the
density was increased 3% for the carbonated blocks with 0.45% dose
of the admixture. As with other mixes, the final desired properties
of the blocks will determine whether admixture, such as sodium
gluconate, is used, and under what conditions, e.g., at what
concentration, which can be pre-determined by preliminary testing
or by other appropriate test.
[0565] This example illustrates the importance of tailoring
carbonation conditions, e.g., admixture usage, to the exact mix
design being considered, in that the three mixes used showed
differing responses to sodium gluconate as an admixture, and also
had different requirements. For example, in the lightweight mix,
density is an important consideration and may dictate that a lower
dose of admixture be used than that that produces maximum strength
development and/or minimum water absorption. For other mixes, other
considerations may play a dominant role in determining carbonation
conditions, such as use of admixture.
Example 15
[0566] This example illustrates the use of a sodium gluconate
admixture with a medium weight mix design, where the admixture dose
was pre-determined based on results from the batches tested in
Examples 13 and 14.
[0567] A Medium Weight mix design was used at the same facility and
with the same equipment as in Examples 13 and 14. The mix design is
given in Table 15.
TABLE-US-00015 TABLE 15 Medium Weight Mix Design (target w/c =
0.78) Ingredient Amount Fraction Birdseye Gravel 1030 lbs 12.8%
Illinois Product Cement 675 lbs 8.4% McCook Block Sand 1800 lbs
22.3% Meyers Torp Sand 2270 lbs 28.1% Screening 2300 lbs 28.5%
RainBloc 80 34 z --
[0568] It was found that the best dose of sodium gluconate in the
Standard, Lightweight, and Sandstone mixes used in Examples 13 and
14 was linearly related to cement content. See FIG. 39. Based on
this relationship, and adjusted for the fact that the CO.sub.2 dose
was to be 1.0% rather than 1.5% used in the Standard, Lightweight,
and Sandstone, a sodium gluconate dose of 0.25% bwc was used.
Blocks were produced as described in Example 13, with
uncarbonated-sodium gluconate (control), uncarbonated+sodium
gluconate, carbonated-sodium gluconate, and carbonated+sodium
gluconate, and tested for compressive strength and density. The
blocks were also submitted for third party testing which also
included water absorption (Nelson Testing Laboratories, Schaumberg,
Ill.).
[0569] Compressive strength and mass results for 7, 28, and 56 days
are summarized in FIG. 40. The direction of the arrows represents
time of measurement, from 7 to 56 days. The uncarbonated blocks
with sodium gluconate were slightly denser and stronger than
uncarbonated blocks without sodium gluconate at all time points
tested, while the carbonated blocks without sodium gluconate were
lower in strength and mass than uncarbonated without sodium
gluconate, and the carbonated with sodium gluconate were both
stronger and lighter than the uncarbonated without sodium
gluconate.
[0570] The results of third party testing are shown in FIG. 41.
Three block data sets were used, with all batches meeting ASTM C90
specification. CO.sub.2 alone made the blocks 6% weaker than
control, but using CO.sub.2 plus sodium gluconate made it 8%
stronger than control. CO.sub.2 alone increased water absorption by
7% compared to control, but CO.sub.2 plus sodium gluconate resulted
in blocks with 4% lower water absorption compared to control.
Shrinkage was increased for both CO.sub.2 and CO.sub.2 plus
gluconate sets, but for the sodium gluconate batch it was
effectively equivalent to the control.
[0571] This example demonstrates that a pre-determined sodium
gluconate dose for a new mix, based on previous results, was
sufficient to produce carbonated blocks comparable in mass and
shrinkage, greater in compressive strength, and lower in water
absorption than uncarbonated blocks without sodium gluconate.
Example 16
[0572] The following protocols were used in EXAMPLES 17 to 21, with
modifications as indicated in particular examples.
[0573] Mortar Mix [0574] 1. Prepare the mixing bowl by dampening
the sides with a wet cloth, be sure to remove any pooling water
from the bowl before introducing raw materials. [0575] 2. Weigh the
necessary amount of water for your test and add the water to the
damp, empty mixing bowl. [0576] 3. Add sand to mixer [0577] 4.
Blend sand and water for 30 seconds on Speed #2 [0578] 5. Scrape
the sides of the bowl with pre wet rubber spatula to remove any
materials sticking to the sides of the mixing bowl [0579] 6. Add
the required cementitious materials to the mixing bowl [0580] 7.
Blend Sand, water and cementitious materials for 30 seconds at
Speed #2 [0581] 8. Record the time that cementitious materials are
added to the mix [0582] 9. Scrape the sides of the mixing bowl with
a pre wet rubber spatula [0583] 10. Record the temperature [0584]
11. If you are not carbonating, skip to step 14 [0585] 12.
Carbonate at a flow rate of 20 liters per min for desired duration.
[0586] 13. Record final temperature [0587] 14. Scrape the sides of
the bowl with pre wet rubber spatula [0588] 15. Introduce necessary
admixtures--the mixing sequence and dosing details of the
admixtures and additives may vary according to test. Record time
and dosage. [0589] 16. After each admixture or sugar is added,
blend for 30 seconds [0590] 17. Measure slump using the Japanese
slump cone. Record slump and spread (two measurements). [0591] 18.
For slump retention, return to bowl, wait, remix 30 sec before next
slump. [0592] 19. Produce a sample for calorimetry [0593] 20. Fill
three mortar cubes molds with mortar (Procedure ASTM C109/C109M--12
Standard Test Method for Compressive Strength of Hydraulic Cement
Mortars) [0594] 21. Cover mortar cubes with a plastic garbage bag
or damp cloth and demold only after 18+/-8 hours have passed [0595]
22. Break cubes at 24 hours+/-30 minutes (use time that cement was
introduced into the mix as an indicator of when samples should be
broken)
[0596] Concrete Mix [0597] Wet inside mixer, add all stone and
sand, mix 30 seconds to homogenize [0598] Add all cementitious
materials, mix one minute to homogenize [0599] Add all batch water
over a period of 30 seconds, mix all materials for one minute
[0600] Take initial temperature [0601] Control batch--mix for 4
minutes and take final temperature. Add admixtures as required, mix
one minute [0602] Carbonated mix--inject CO.sub.2 gas at 80 LPM,
enclose mixer, mix while carbonating for required time [0603]
Remove cover and record final temperature, Add admixtures as
required, mix one minute [0604] Record slump (ASTM C143) and cast 6
compressive strength cylinders (ASTM C192) [0605] Take two samples
for moisture/carbon quantification bake off, one sample for
calorimetry [0606] Demould cylinders after 28+/-8 hours and place
them in a lime water bath curing tank at a temperature of
23.degree. C.+/-3.degree. C. [0607] Test compressive strength 24
hours (3 samples) and 2 at 7 days (2 samples)
Example 17
[0608] In this example the carbon dioxide uptake of cements from
two different sources, Lehigh and Holcim, were compared.
[0609] Mortar mix made under a 20 LPM flow of CO.sub.2 gas. Samples
were removed from the batch of mortar every 60 s until the 8 minute
point. The carbon dioxide content was measured and a curve
constructed relating the length of exposure to CO.sub.2 gas to the
approximate amount of CO.sub.2 uptake. Two cements were compared.
Mix design was 1350 g EN sand, 535 g of cement, 267.5 g of water.
w/c=0.5.
[0610] The results are shown in FIG. 42. Carbon dioxide uptake
increased with time, as expected, but the rate of increase was
different for the two different cements. At a w/c of 0.5, the
mortar paste can absorb carbon dioxide but to exceed 1% uptake
would take 3 to 5 minutes, depending on the cement type used.
[0611] This Example illustrates that a w/c of 0.5 allows carbon
dioxide uptake, but at a rate that may not be compatible with mix
times in some settings, and that the source of the cement can
affect the properties of a hydraulic cement mix made with the
cement regarding carbon dioxide uptake.
Example 18
[0612] In this Example, the effect of w/c ratio on carbon dioxide
uptake was studied.
[0613] In a first study, a test performed with mortar. The total
mix was 990 g of Ottawa sand, 440 g cement, with 206 g of total
water. Water, sand and cement were mixed, with the water added in
two stages. CO.sub.2 was supplied for various times at 10 LPM after
the first water addition, which brought the mix to either 0.1 or
0.45 w/c, and the remaining water was then added and mixing
completed. Carbon uptake at various time points was measured, as
shown in FIG. 44. The rate of carbon dioxide uptake was higher for
the paste with w/c 0.1 at time of reaction than for w/c of
0.45.
[0614] In a second study, a series of tests were performed on
mortar. Mortar mix made under a 20 LPM flow of CO.sub.2 gas. The
carbon dioxide content was measured and a curve constructed
relating the w/c of the mortar mix at the time of carbon dioxide
addition to the approximate amount of CO.sub.2 uptake. Mix design
was 1350 g EN sand, 535 g of cement (Holcim GU), 267.5 g of water.
Total w/c=0.5 Water was added in two stages. One portion before
carbonation, the remaining portion after 1 min of carbonation. The
amount before carbonation ranged from 10% to 100% of total
(w/c=0.05 to 0.50). The effect of w/c on carbonation at 1 minute is
shown in FIG. 45 and Table 16.
TABLE-US-00016 TABLE 16 Effect of w/c in mortar on carbon dioxide
uptake Relative to initial w/c Uptake 0.05 level 0.50 0.00 0.05
1.98 100% 0.10 1.56 79% 0.15 1.52 77% 0.20 1.29 65% 0.25 1.32 67%
0.30 1.24 63% 0.35 0.77 39% 0.40 0.78 40% 0.45 0.48 24% 0.50 0.35
18%
[0615] Drier mortar systems showed higher rates of uptake than did
wet systems. 1.98% uptake at 0.05 w/c declined to 0.35% at 0.50
w/c.
[0616] In a third test, a trial concrete mix was prepared with
split water additions. The total mix was 300 kg/m.sup.3 cement, 60
fly ash, 160 water, 1030 stone, 832 sand. The water was added in
two stages. CO.sub.2 supplied for 180 seconds at 80 LPM after the
first water addition. Remaining water then added and mixing
completed. The w/c at carbon dioxide addition was 0.1, 0.15, or
0.45. The results are shown in FIG. 46. As with mortars, the carbon
uptake increased with lower w/c when the carbon dioxide is
delivered.
Example 19
[0617] This example illustrates that temperature rise during
carbonation of a hydraulic cement mix is highly correlated with
degree of carbonation and can be used as an indicator of degree of
carbonation in a specific system.
[0618] In a first test, the mortar used in the second test of
Example 17 also had temperature measurements taken at the various
time points. The results are shown in FIG. 47. There was a linear
relationship between degree of carbonation and temperature increase
in this system, in which w/c was varied and carbon dioxide exposure
was kept constant.
[0619] In a second test, temperature vs. carbon dioxide uptake was
studied in mortars prepared with three different cements, Holcim
GU, Lafarge Quebec, and Lehigh. Mortar was prepared at a w/c=0.5
and carbonated for various times at 20 LPM CO2. The results are
shown in FIG. 48. There was also a linear relationship between
degree of carbonation and temperature rise in this system, in which
w/c was kept constant at 0.5 and time of carbon dioxide exposure
was varied. The relationship was relatively constant over different
cement types. The slopes of the line differ in the two tests, which
were conducted in two different systems, reflecting the specificity
of temperature rise with carbonation to a particular system.
[0620] These results indicate that in a well-characterized system,
temperature increase may be used as a proxy indicator for carbon
dioxide uptake.
Example 20
[0621] This example illustrates the effects of different admixtures
on slump and compressive strength in concrete.
[0622] In a first test, sodium gluconate at 0, 0.1% or 0.2% was
added to a concrete mix after carbonation and the effects slump at
1, 10 and 20 minutes after mixing were measured, and compared to
control, uncarbonated concrete. The results are shown in FIG. 49
and Table 17. The slump of the carbonated concrete is less than
half of the control at 1 min and declines to no slump at 10 min.
Adding 0.1% sodium gluconate after carbonation gave a slump equal
to the control at 1 min, 80% at 10 min and 50% at 20 min. Adding
0.2% also provided high slump than the lower dose at all intervals,
before being 75% of the control at 20 min.
TABLE-US-00017 TABLE 17 Effects of sodium gluconate on concrete
slump Control CO.sub.2 Control SG - 0.1% SG - 0.2% 1 min 100% 46%
100% 108% 10 min 100% 0% 80% 140% 20 min 100% 0% 50% 75%
[0623] In a second test, the effects of fructose at various
concentrations on initial slump of a concrete mix were tested.
Fructose was added after carbonation. Total mix was 4.22 kg cement,
1 kg fly ash, 3.11 kg water, 16.96 kg stone, 14.21 kg sand. The
results are shown in FIG. 50. Carbonation reduced the slump of the
concrete. In response, fructose was added after carbonation is
proportions of 0.05, 0.10 and 0.20% by weight of cement. The
dosages reflect solid mass of additive delivered in a solution. The
CO.sub.2 content was quantified as 1.3%, 1.4% and 1.5% by weight of
cement for the three carbonated batches respectively. 0.20%
fructose was sufficient to restore the slump to be equivalent to
the control. However, fructose had a strength retarding effect, as
shown in FIG. 51. Strength at 24 hours was significantly less than
uncarbonated control, but strengths at 7 days was acceptable, with
higher strengths associated with higher fructose contents.
Example 21
[0624] In this example, a variety of different cements were tested
in a mortar mix to determine variations in response to
carbonation.
[0625] Six cements were tested: Holcim GU (Hol), Lafarge Quebec
(LQc), Lafarge Brookfield (LBr), Lehigh (Leh), Illinois Product
(Ipr), and Northfield Fed White (NWh). The properties and
chemistries of the different cements are given in Table 18.
TABLE-US-00018 TABLE 18 Properties and chemistries of different
cements Metric Hol LQc LBr Leh IPr NWh Surface Area - 423 417 392
425 501 408 Blaine (m.sup.2/kg) Free CaO (%) 0.31 0.94 0.16 1.45
1.45 1.47 CaO (%) 62.22 60.56 62.68 61.55 62.61 65.36 Na.sub.2Oe
(%) 0.28 0.38 0.18 0.11 0.41 0.08 SiO.sub.2 (%) 20.30 19.18 20.10
19.53 19.12 21.41 Al.sub.2O.sub.3 (%) 4.62 4.72 5.24 4.45 5.47 4.38
TiO.sub.2 (%) 0.22 0.21 0.26 0.32 0.29 0.08 P.sub.2O.sub.5 (%) 0.14
0.26 0.05 0.25 0.13 0.01 Fe.sub.2O.sub.3 (%) 2.50 2.74 2.27 3.00
2.23 0.20 MgO (%) 2.21 2.80 1.48 3.21 2.70 0.90 Na.sub.2O (%) 0.22
0.32 0.11 0.06 0.34 0.06 K.sub.2O (%) 0.92 0.84 1.09 0.70 1.01 0.28
Mn.sub.2O.sub.3 (%) 0.05 0.09 0.07 0.18 0.19 0.01 SrO (%) 0.08 0.24
0.06 0.04 0.07 0.03 SO.sub.3 (%) 3.63 3.79 4.10 2.96 3.88 3.94 BaO
(%) 0.06 0.05 0.13 0.05 0.05 0.08 ZnO (%) 0.04 0.07 0.00 0.02 0.01
0.00 Cr.sub.2O.sub.3 (%) 0.01 0.03 0.01 0.01 0.01 0.00 Loss on 2.52
4.08 2.38 3.54 1.98 3.00 ignition to 975.degree. C. (%)
[0626] The mortar mix was EN 196 Sand 1350 g, Cement 535 g, Water
267.5 g, w/c Ratio 0.5. CO.sub.2 was added to the mixing bowl at 20
LPM for durations of 0, 2, 4, 6, and 8 minutes. Temperature change,
slump, flow-spread, CO.sub.2 uptake, and 24 hr cube strength were
measured. The results are given in Table 19.
TABLE-US-00019 TABLE 19 Properties of carbonated mortars made with
different cements Hol LQc LBr Leh IPr NWh 0 min CO.sub.2 CO.sub.2
Uptake (% bwc) 0.00 0.00 0.00 0.00 0.00 0.00 Delta T (.degree. C.)
0.0 1.1 1.2 0.7 1.3 1.0 Slump (mm) 110 115 100 110 95 105 Slump (%
of Control) 100% 100% 100% 100% 100% 100% Work (mm) 157 185 144 165
130 180 Strength (MPa) 20.2 15.0 25.1 16.0 33.4 20.4 Strength (% of
Control) 100% 100% 100% 100% 100% 100% 2 min CO.sub.2 CO.sub.2
Uptake (% bwc) 0.87 0.64 0.47 0.67 0.55 0.69 Delta T (.degree. C.)
2.9 3.6 2.8 4.3 3.7 6.5 Slump (mm) 70 105 40 50 10 30 Slump (% of
Control) 64% 91% 40% 45% 11% 29% Work (mm) 83 140 58 60 10 35
Strength (Mpa) 9.9 7.6 12.0 13.1 31.3 17.3 Strength (% of Control)
49% 38% 48% 65% 94% 85% 4 min CO.sub.2 CO.sub.2 Uptake (% bwc) 0.94
0.88 1.10 1.30 1.79 0.88 Delta T (.degree. C.) 4.9 6.1 7.6 7.2 9.3
9.3 Slump (mm) 60 70 20 45 0 8 Slump (% of Control) 55% 61% 20% 41%
0% 8% Work (mm) 75 78 21 45 0 10 Strength (MPa) 9.9 8.1 11.2 10.9
27.5 16.4 Strength (% of Control) 49% 40% 45% 54% 82% 80% 6 min
CO.sub.2 CO.sub.2 Uptake (% bwc) 1.96 1.74 4.06 1.84 2.71 1.57
Delta T (.degree. C.) 7.6 9.2 9.7 11.2 13.2 12.7 Slump (mm) 35 70 0
35 0 0 Slump (% of Control) 32% 61% 0% 32% 0% 0% Work (mm) 35 89 -6
37 0 0 Strength (MPa) 8.8 6.4 11.2 13.4 29.5 -- Strength (% of
Control) 43% 32% 45% 66% 88% -- 8 min CO.sub.2 CO.sub.2 Uptake (%
bwc) 2.76 1.68 1.27 2.23 3.75 2.07 Delta T (.degree. C.) 13.4 9.2
14.8 14.7 22.2 17.3 Slump (mm) 5 40 0 15 0 0 Slump (% of Control)
5% 35% 0% 14% 0% 0% Work (mm) 5 44 -8 13 0 0 Strength (MPa) 8.2 6.8
13.9 14.5 -- -- Strength (% of Control) 41% 34% 56% 72% -- --
[0627] There was considerable variation among the mortars made from
the different cements in slump and strength. The Illinois Product
was notable for its higher compressive strength at all time points
tested. Without being bound by theory, this may be due to its
greater surface area (see TABLE 18), which allows it to absorb
carbon dioxide with relatively less proportional impact on strength
development. Strength vs. surface area of carbonated mortar mixes
with various surface areas is shown in FIG. 52.
Example 22
[0628] In this example, various admixtures were added to cement
paste mixes exposed to carbon dioxide and their effects on slump
after mixing were determined. The paste mix was 500 g cement, 250 g
water. Holcim GU cement. 1% bwc CO2 was dosed, with mixing for one
minute. The results are shown in TABLE 20.
TABLE-US-00020 TABLE 20 Effects of admixtures on slump of
carbonated mortar Condition Paste Spread (cm) (all doses expressed
as 1 Min after Paste Spread (cm) % by weight of cement) mixing 10
Min after mixing Control 11.5 13.75 1% CO.sub.2 8.75 5 1% CO.sub.2
+ 1% Na.sub.2SO.sub.4 9.75 4.25 1% CO.sub.2 + 3% Na.sub.2SO.sub.4
7.25 4 1% CO.sub.2 + 5% Na.sub.2SO.sub.4 4.75 4 1% CO.sub.2 + 0.04%
Citric Acid 6.75 4 1% CO.sub.2 + 0.10% Gluconate 6.5 4.25 1%
CO.sub.2 + 0.15% Gluconate 9.25 9.75 1% CO.sub.2 + 0.20% Gluconate
9.25 10.25 1% CO.sub.2 + 0.05% Gluconate - 9.75 4.75 After
Carbonation 1% CO.sub.2 + 0.10% Gluconate - 10.75 11.775 After
Carbonation 1% CO.sub.2 + 0.15% Gluconate - 13.5 14 After
Carbonation
Example 23
[0629] In this Example, sensors for carbon dioxide and moisture
were used in a mixing operation.
[0630] A precast operation was performed using the following mix
components:
TABLE-US-00021 Aggregate Fine Shaw Resources 602 kg Sand Aggregate
Coarse 3/8'' Coldstream 200 kg Aggregate Coarse Granodiorite 839 kg
Cement Cement Maxcem 286 kg Admix Rheopel Plus 400 ml Admis Rheofit
900 350
[0631] Two carbon dioxide sensors were used, Sensor 1 positioned
adjacent to an access hatch to the mixer and Sensor 2 positioned at
the ejection location of the mixer, at a door that discharges onto
a belt. CO.sub.2 dose was increased or decreased depending on the
overspill, as detected by the two sensors.
[0632] They are involved in a two stage injection approach. [0633]
1. Fill--high flowrate to fill the mixer with CO.sub.2 [0634] 2.
Supply--lower flowrate to maintain a supply as CO.sub.2 is absorbed
by the concrete. [0635] The PLC was programmed as follows to make
changes based on the readings of the CO.sub.2 sensors: [0636]
Sensor 1 to be placed by door, sensor 2 placed by mixer exit
(measure each sensor separately) [0637] If sensor 1 exceeds X ppm
during flow 1, go to flow 2 [0638] If sensor 1 exceeds X ppm during
flow 2, reduce flow by reduce percentage [0639] If sensor 2 exceeds
Y ppm ever, reduce max mix time by reduce time [0640] If either
sensor exceeds 5000 ppm for more than 5 mins, pop-up alarm on
screen [0641] If either sensor exceeds 5000 ppm for more than 10
mins, shut off system [0642] If either sensor exceeds 9000 ppm,
shut system off [0643] X and Y were programmable under each recipe
(this allows change if a plant has a high CO2 baseline due to dust
etc.). Flow 1 was programmable and was the flow that was used to
fill the headspace quickly (usually 1500 LPM). Flow 2 was
calculated by the PLC and was based on max mix time, CO.sub.2 dose
and the total already in the headspace. Max mix time was
programmable and was the total desired injection time. Reduce
percentage and reduce time were programmable and were determine by
what percentage to reduce either the flowrate (thus reducing total
CO2 dosage) or the max mix time (thus increasing flowrate to inject
in shorter time).
[0644] The system was used over several batches and the results are
shown in FIG. 53. The top line of FIG. 53 indicates the actual
CO.sub.2 dosed, and the second line indicates CO.sub.2 detected in
the mix. The efficiency of uptake varied from 60 to 95%. The bottom
two lines indicate maximum values detected at Sensor 1 (all batches
including Batch 3) and Sensor 2 (Batches 4-10). Average values may
produce a better result.
[0645] This example demonstrates that carbon dioxide sensors may be
used to adjust the flow of carbon dioxide in a cement mixing
operation, producing uptake efficiencies up to 95%.
Example 24
[0646] This example demonstrates the use of solid carbon dioxide
(dry ice) as a delivery mode for carbon dioxide in mixing
concrete.
[0647] A solid particle of carbon dioxide will sublimate when in
contact with the mix water, thereby releasing carbon dioxide gas
over the period of time required to consume the particle. To
achieve an extended dosing of carbon dioxide, e.g., in a readymix
truck, solid carbon dioxide can be added in the desired mass and
quantity, and in appropriate shape and size, to effectively provide
a given dose of carbon dioxide over a desired length of time. The
shape and size of the solid carbon dioxide will determine the total
surface area of the solid; the greater the surface area, the
greater the rate of sublimation of the dry ice.
[0648] Two dosing procedures were used. In the first, dry ice in
the form of one inch pellets was used. In the second, a square slab
with a 2'' by 2'' cross section was cut to the appropriate length
to provide the desired dose. Mixing was performed in either a small
drum mixer (17 liters) or large drum mixer (64 liters), and the
mixing was conducted with a cover unless otherwise indicated.
[0649] Pellet Delivery:
[0650] A mix design of 400 kg/m.sup.3 cement, 175 kg/m.sup.3 water,
1040 kg/m.sup.3 stone, and 680 kg/m.sup.3 sand was used. Cement in
one batch was 26.14 kg.
[0651] In a first batch, CO.sub.2 at 0.5% bwc dose of pellets (34
g) was added with the other mix materials and the concrete was
mixed for 2 minutes. Uptake was found to be 014% bwc, and a
1.degree. C. temperature increase was noted. The dry ice pellets
had not completely sublimed after 2 min of mixing.
[0652] In a second batch, CO.sub.2 at 1.0% bwc dose of pellets (68
g) was added with the other mix materials and the concrete was
mixed for 4 minutes. CO.sub.2 uptake was 0.3% bwc with a 1.degree.
C. temperature increase. After 4 min of mixing, all the dry ice
pellets had completely sublimed.
[0653] In a third batch, CO.sub.2 at 2.75% bwc dose of pellets (186
g) was added with the other mix materials and the concrete was
mixed for 4 minutes. CO.sub.2 uptake was 0.6% bwc with a 2.degree.
C. temperature rise; all dry ice pellets were sublimed after 4 min
of mixing.
[0654] With the use of pellets, uptake increased with increasing
pellet dose, and pellets of this size and in these doses took 2 to
4 min to completely sublime. CO.sub.2 uptake was low efficiency,
and the gas uptake was associated with mix stiffening.
[0655] Slab Delivery:
[0656] In a first test, the same mix design as for the pellet tests
was used. The 2.times.2'' slab was cut to 5.5'' long for a dose of
2% CO.sub.2 bwc. In a first batch, water was added in two
additions. A first addition of water to w/c of 0.2 was performed,
the dry ice slab was added and mixed for 40 seconds. Final water
was added to the total water amount and the concrete was mixed for
an additional 6 min. The CO.sub.2 uptake was 0.95% and no
temperature increase was observed. In a second batch, 4 serial
addition of slabs of dry ice were performed. All water was added to
the mix (w/c 0.44) then a dry ice slab was added for a dose of 2%
bwc. The concrete was mixed for 6 min. CO.sub.2 uptake was 0.67%
and no temperature increase was observed. An additional slab of dry
ice was added to the mix, at 2% bwc for a total dose of 4% bwc, and
a further 6 minutes of mixing was performed. CO.sub.2 uptake was
1.67%, and no temperature increase was observed. An additional slab
of dry ice was added to the mix, at 2% bwc for a total dose of 6%
bwc, and a further 6 minutes of mixing was performed. CO.sub.2
uptake was 2.33%, and a 3.5.degree. C. temperature increase was
observed. An additional slab of dry ice was added to the mix, at 6%
bwc for a total dose of 12% bwc, and a further 6 minutes of mixing
was performed. CO.sub.2 uptake was 3.44%, and a 5.degree. C.
temperature increase was observed. In this test, in which mixing
was at full speed, all the carbon dioxide was completely sublimed
at the end of each mixing time. Subsequent tests were performed at
lower speed representative of a truck in transit rather than a
truck in initial mixing stage.
[0657] In a second test, the same mix design as for the pellets was
used except the final proportion of water was 200 kg/m.sup.3. Slow
mixing (.about.1 RPM) in a 65 L mixer was performed, with a dry ice
slab added 2 min after the initial cement and water contact, for a
dose of 2% bwc. Mixing was continued for a total of 36 min.
CO.sub.2 uptake was 0.95%, and a 3.5.degree. C. temperature
increase was observed. The slump of the concrete mix prior to
CO.sub.2 addition was 6'', and 3'' after 36 min of mixing under
CO.sub.2.
[0658] In a third test, the same mix design as for the pellet tests
was used. Water was added to an initial w/c of 0.2, a dry ice slab
was added for a dose of 0.2% bwc, and the concrete mix was mixed
for 40 s at full speed (45 rpm), then the remainder of the water
was added, to a w/c of 0.45 and the mix was mixed for 36 min of
slow (transit, .about.1 RPM) mixing of the batch in a 65 L mixer.
CO.sub.2 uptake was 0.75%, and a 1.5.degree. C. temperature
increase was observed. Slump was 5.5'' after 36 min of mixing. A
control slump (without carbon dioxide) was assumed to be
.about.6''. Then another 2% bwc of dry ice slab was added, and the
concrete was mixed at high speed for an additional 11 min. CO.sub.2
uptake was 1.66%. Slump decreased from 5.5'' to 2.5.''
[0659] In a fourth test, the same mix design as for the pellet
tests was used, except water was 195 kg/m.sup.3. Two batches were
run in which dry ice at a dose of 2% bwc was added 2 minutes after
the initial cement and water contact. In the first batch, the
concrete was mixed with cover on at a fast transit mix (.about.2
RPM) for 30 min. CO.sub.2 uptake was 1.3% bwc, and a 5.degree. C.
temperature increase was observed. Slump was 0'' after mixing,
compared to 6.5'' slump in control (no carbon dioxide). In the
second batch, mixing was done with cover off at a fast transit mix
for 29 min. CO.sub.2 uptake was 0.7% bwc, and a 0.2.degree. C.
temperature increase was observed. Slump was 3'' after 29 min
mixing, compared to 6.5'' slump in control (no carbon dioxide).
[0660] This example demonstrates that the size and shape of dry ice
can be used to control delivery, and that various times of
addition, mix rates, water contents, and other variables may be
manipulated to modulate the amount of carbon dioxide taken up by
the concrete and the effect of the carbon dioxide on such factors
as slump.
Example 25
[0661] This example illustrates the use of low-dose carbon dioxide
to provide accelerated hydration, early strength development and
set, with minimal impact on rheology and later-age strength.
[0662] Mortar Tests
[0663] In a first set of tests, mortars were prepared. Mortars were
prepared with 1350 g sand, 535 g cement, and 267.5 g water, and
homogenized in a paddle-style mixer by mixing on low speed for
.about.2 min, then samples were removed for CO.sub.2 analysis and
calorimetry. The mortar was then exposed to CO.sub.2 gas at a flow
rate of .about.0.15 LPM for 2 minutes and additional samples were
removed. This same mortar was exposed to 3-7 successive rounds of
carbonation total, with samples removed between each round.
[0664] In one test, Holcim GU cement was used. The levels of
carbonation of the mortar achieved in succeeding rounds of carbon
dioxide exposure were 0, 0.05, 0.10, 0.20, 0.48, and 0.70% bwc.
FIG. 54 presents data on isothermal calorimetry power curves for
the different levels of carbonation, showing that by carbonating
the mortar the rate of cement hydration could be accelerated
(curves shift to the left and become steeper with carbonation). The
total heat evolution was also improved at early ages with
carbonation of the mortars (FIG. 55).
[0665] In addition, the onset of both initial and final set was
accelerated by carbonation, as indicated by penetrometer
measurements and shown in FIG. 56. For these measurements, mortar
was prepared as follows: 5.times. batch size in Hobart (normal
batch scaled up 500% to use in a larger mixer) 1337.5 g water, 2675
g cement 5175 g sand. Combined in Hobart mixer and homogenized.
Carbonated at 1.0 LPM for 5 rounds of 2 minutes (i.e. 0, 2, 4, 6,
8, 10 minutes samples). Penetrometer measurement performed on last
sample (10 minutes total CO.sub.2 exposure). Expected dose for 1
LPM for 10 min is about 20 g of CO.sub.2, for a total dose is about
0.74% bwc. From Eltra: carbon dioxide uptake estimated at 0.10%
bwc. The low uptake may have been due to head space/flow rate. A
Control was then cast for comparison afterwards. 2.times. batch
size in Kitchen Aid (smaller mixer): 1070 g cement, 535 g water,
2070 g sand.
[0666] Similar results were seen for mortars prepared with Lafarge
Brookfield GU cement dosed at 0, 0.07 0.14, and 0.22% bwc carbon
dioxide, as shown for hydration in FIG. 57, as well as early
strength development as shown in FIG. 58.
[0667] Concrete Tests
[0668] Tests were extended to concretes. In a typical experiment a
batch of concrete was prepared with the following proportions: 16.0
kg sand, 23.80 kg stone, 9.18 kg cement, 3.15 kg water. The
concrete was homogenized in a drum-style mixer by mixing on low
speed for .about.2 min and samples were removed for CO.sub.2
analysis and calorimetry. The concrete was then exposed to CO.sub.2
gas at a flow rate of .about.2.0 LPM for 2 minutes and additional
samples were removed. This same concrete was exposed to three
successive rounds of carbonation in total, with samples removed
between each round. Total CO.sub.2 uptake for succeeding rounds was
0, 0.10, 0.15, and 0.20% bwc.
[0669] In a first series, LaFarge Brookfield GU cement was used in
the concrete. Calorimetry power curves show acceleration of
concrete. See FIG. 59. Calorimetry energy curves show an increased
amount of heat released at all ages in the carbonated concrete. See
FIG. 60. Early strength development was also accelerated in the
carbonated concretes. See FIG. 61. In addition, set time
measurements confirmed that the observed acceleration of hydration
translated into accelerated initial (500 psi) and final (4000 psi)
set in the carbonated concrete. FIG. 62 shows penetrometer readings
over time for carbonated concrete (approximately 0.20% bwc CO.sub.2
uptake) compared to uncarbonated.
[0670] Similar results were obtained in a second series, where
concrete was produced with St. Mary's B cement; for example,
carbonation at 0.08, 0.17, and 0.35% bwc all produced increased
8-hour and 12-hour compressive strength compared to uncarbonated
control. See FIG. 63.
[0671] Other concretes were produced using St. Mary's HE cement and
Holcim GU cement (carbonated at a single level of CO.sub.2 uptake).
The concretes were carbonated at a constant carbon dioxide exposure
of delivered carbon dioxide at a rate of 0.10-0.15% bwc per minute
over three minutes (2 min with carbon dioxide flow and one minute
of lid on mixing after delivery) for a total dose of 0.20-0.30%
carbon dioxide bwc. Carbonation level was 0.15% bwc in the Holcim
GU mixture and 0.26% bwc in the St Mary's HE mixture. See Table
21.
TABLE-US-00022 TABLE 21 Properties of low dose carbonated concretes
Initial Set Final Set Strength Acceleration Acceleration Strength
at 8 hr at 8 hr Cement ID (minutes) (minutes) (% of control) (MPa)
St. Mary's HE 55 41 133 2.2 Holcim GU 61 70 149 1.3
[0672] In an industrial trial, a truck carrying 2 m3 of concrete
was delivered to the lab, with a mix design of 1930 kg sand, 2240
kg stone, 630 kg LaFarge Brookfield GU cement, and 238 kg water. A
sample of uncarbonated concrete was first removed from the truck to
cast control samples. The truck was then subjected to 6 separate
doses of 0.05% bwc CO.sub.2. Enough concrete was removed to satisfy
casting demands following each dose (.about.60 L). The fresh
properties of the concrete are shown in Table 22.
TABLE-US-00023 TABLE 22 Fresh properties of readymix concrete at
low dose carbonation Total Temp at Air Defoamer Mighty CO.sub.2
dose Time of discharge Slump Content Dose 21ES dose Sample # Sample
ID (bwc) discharge (.degree. C.) (inches) (%) (% bwc) (% bwc) 1
Control 0 8:45 14.7 3.5 1.5 0.10 0.10 2 CO.sub.2-1 0.05 8:50 16.4
3.5 n/a 0.10 0.10 3 CO.sub.2-2 0.10 9:04 16.7 3.5 n/a 0.10 0.10 4
CO.sub.2-3 0.15 9:12 18.0 3.0 n/a 0.10 0.10 5 CO.sub.2-4 0.20 9:26
18.4 3.0 n/a 0.10 0.10 6 CO.sub.2-5 0.25 9:35 18.5 1.5 n/a 0.10
0.10 7 CO.sub.2-6 0.30 9:50 18.7 2.0 n/a 0.10 0.15
[0673] In general, the compressive strength of the concrete
specimens increased with each additional round of carbonation. This
was most evident at early ages (up to 74% increase at 12 hours) but
persisted until later ages (5% compressive strength increase at 7
days). See FIGS. 64 (12 hours), 65 (16 hours), 66 (24 hours), and
67 (7 days).
[0674] This example illustrates that the use of low-dose carbon
dioxide in mortar and concrete mixes can accelerate set and
strength development compared to uncarbonated mortar and concrete
mixes.
Example 26
[0675] This example demonstrates the use of sodium gluconate in a
dry mix concrete, either carbonated or uncarbonated.
[0676] The mix was 200 g stone, 1330 g sand, 330 g Holcim GU
cement, and 130 g water. The mixing cycle was:
[0677] Mix aggregates and water for 30 s [0678] Add cement and mix
30 s [0679] 60 s mixing, with carbonation if called for [0680] add
admixtures and mix 30 s [0681] Compact cylinders using Proctor
hammer [0682] Dosages employed were 0, 0.02%, 0.04% and 0.06%
sodium gluconate by mass of cement.
[0683] FIG. 68 shows the CO.sub.2 uptake of carbonated specimens.
The masses of the cylinders prepared, a proxy for density since all
cylinder volumes are substantially the same, showed that
carbonation resulted in an 8.4% mass deficit in comparison to the
control, but that the addition of sodium gluconate increased the
mass of the carbonated specimens, proportional to the dose, so that
at a dose of 0.06% sodium gluconate, the mass deficit was reduced
to 5.5%, whereas none of the three sodium gluconate doses had an
effect on the compaction of the control samples. See FIGS. 69 and
70. Retardation was quantified through calorimetry by determining
the amount of energy released through the first 6 hours following
the mix start. Carbonation caused a decrease in energy released, as
did the addition of sodium gluconate; in carbonated specimens the
reduction in energy released was 19% at the highest sodium
gluconate dose, whereas in uncarbonated specimens the reduction in
energy released was 53% at the highest sodium gluconate dose. See
FIGS. 71 and 72.
Example 27
[0684] This example demonstrates the effects of increasing free
lime on carbon dioxide uptake and hydration.
[0685] In a first test, mortars were prepared with added CaO (1.5%
bwc), NaOH (2.2% bwc), or CaCl.sub.2 (3% bwc), carbonated, and
compared to control. A standard mortar mix of 535 g cement, 2350 g
sand, and 267.5 g water was used. The sand and water were combined
and mixed for 30 s, followed by cement addition (with added powder
if used) and an additional 60 s mixing. Initial temperature was
recorded, then the mortar was mixed for 60 s under 20 LPM CO.sub.2
flow, mixing was stopped and temperature recorded and sample
removed for CO.sub.2 analysis, then mixing and CO.sub.2 exposure
was resumed for another 60 s and sampling occurred, for a total of
5 min of CO.sub.2 exposure. The results are shown in FIG. 73.
Addition of the alkali species, free lime (CaO) or NaOH, increased
the rate of CO.sub.2 uptake, while the addition of CaCl.sub.2
decreased the uptake rate. The rates of uptake were: 0.34% CO.sub.2
uptake/min (no additive); 0.56% CO.sub.2 uptake/min (CaO), a 66%
increase; 0.69% CO.sub.2 uptake/min (NaOH), a 104% increase; and
0.23% CO.sub.2 uptake/min (CaCl2), a 34% decrease.
[0686] In a second test, two test mortars were compared, one
conventional mortar and one that included an addition of 1.5% CaO
bwc. The mortar mixes were as in the first test. The cement used
had a free lime content of 0.31% bwc before addition of extra CaO;
this is considered to be a low free lime level. The mixing mortar
was subjected to 0, 30, 60, or 90 s of CO.sub.2 at 20 LPM, and
hydration was measured by calorimetry. Energy release was followed
up to 24 hours at 6 hour intervals.
[0687] The results are presented in FIG. 74. When control (no CaO
addition) carbonated vs. uncarbonated mortars were compared, energy
release with 30 s CO.sub.2 was 19% greater in the carbonated
compared to uncarbonated at 6 hours, declining to 7% lower at 24
hours; energy release with 60 s CO.sub.2 was 23% greater in the
carbonated compared to uncarbonated at 6 hours, declining to 12%
lower at 24 hours; energy release with 90 s CO.sub.2 was 21%
greater in the carbonated compared to uncarbonated at 6 hours,
declining to 17% lower at 24 hours. See FIG. 75. In general,
addition of CaO to the mix both increased CO.sub.2 uptake for a
given time of exposure, and increased the energy release at a given
time point, compared to samples without CaO addition. When compared
to a control mortar that contained no added CaO, mortars with added
CaO showed energy release at 97-99% of control at all time points
in uncarbonated samples; in samples exposed to 30 s CO.sub.2,
mortars with added CaO showed energy release 20% higher than
mortars with no added CaO at 6 hours, decreasing to 11% higher at
24 hours, and CO.sub.2 uptake was 56% greater than in mortars with
no added CaO; in samples exposed to 60 s CO.sub.2, mortars with
added CaO showed energy release 33% higher than mortars with no
added CaO at 6 hours, decreasing to 15% higher at 24 hours, and
uptake was 151% greater than in mortars with no added CaO; in
samples exposed to 90 s CO.sub.2, mortars with added CaO showed
energy release 23% higher than mortars with no added CaO at 6
hours, decreasing to 9% higher at 24 hours, and uptake was 151%
greater than in mortars with no added CaO. See FIG. 76.
[0688] This example demonstrates that free lime (CaO) addition to a
mortar both improves the rate of carbon dioxide uptake as well as
hydration, when compared to mortar without added free lime
[0689] Examples 28-32 are directed to delivery of low doses of
carbon dioxide to ready mix trucks, as a gas (Example 27) or liquid
that converts to solid and gas (Examples 29-32), under various
conditions.
Example 28
[0690] This example is an illustration of low dose of gaseous
carbon dioxide treatment of a concrete mix in the drum of a ready
mix truck at a time significantly after the batching of the
concrete, and its effects on early strength.
[0691] The carbon dioxide was dosed into the drum of a ready mix
truck. Carbon dioxide was gaseous. The carbon dioxide was added to
the mix beginning approximately 70 min after batching, in multiple
stages to give a concrete mix with increasingly greater doses of
carbon dioxide so that the final addition was approximately 135 min
post batching. Thus the dosing of CO.sub.2 was well after mixing
started, akin to supplying CO.sub.2 to a truck in transit or at a
job site rather than during batching.
[0692] Mix design was 30 MPa slab mix, 2 m.sup.3 load, truck less
than half full [0693] Sand 1930 kg [0694] Stone 2240 kg [0695] GU
Cement 630 kg [0696] Water 238 kg
[0697] Admixes were added at the test site prior to any
sampling--defoamer 0.10% bwc, superplasticizer (Mighty ES) 0.10%
bwc. Mighty ES was increased for final sample.
[0698] CO.sub.2 was added to the drum from a gas tank with a
regulator. Flow was .about.80 LPM for 2 minutes for each CO.sub.2
dose. Line Pressure was 70 psi. Truck faster mix (25 RPM) "post
dose" for .about.60 s. Transit mix (slow, 5 RPM) remaining
time.
[0699] Dosing was in a serial fashion on the same batch of
concrete--dose, sample, next dose, sample, next dose, etc.
[0700] Time of discharge indicates when concrete was sampled.
Dosing would have occurred within the five minutes immediately
preceding.
[0701] Table 23 shows the conditions for each sample:
TABLE-US-00024 TABLE 23 Conditions for various samples of low dose
carbon dioxide Sample ID Control CO2-1 CO2-2 CO2-3 CO2-4 CO2-5
CO2-6 Time of Discharge 74 79 93 101 115 124 139 (min) Total
CO.sub.2 Dose 0 0.05% 0.10% 0.15% 0.20% 0.25% 0.30% (% bwc)
Temperature (.degree. C.) 14.7 16.4 16.7 18 18.4 18.5 18.7 Slump
(inches) 3.5 3.5 3.5 3 3 1.5 2 Air Content (%) 1.5 n/a n/a n/a n/a
n/a n/a Defoamer 0.10% 0.10% 0.10% 0.10% 0.10% 0.10% 0.10% (% bwc)
Mighty ES 0.10% 0.10% 0.10% 0.10% 0.10% 0.10% 0.15% (% bwc)
CO.sub.2 Uptake -- inconclusive (% bwc)
[0702] 12-hour, 16-hour, 24-hour, 7-day, 28-day strengths are shown
in Tables 24 (absolute values) and 25 (values relative to control,
uncarbonated concrete). Three specimens were taken at each age as
4''.times.8'' cylinders with reusable end caps. Specimens were kept
in moist curing storage until testing. Calorimetry data is shown in
FIGS. 77A (power vs. time) and 77B (energy vs. time) for Control,
CO2-1, 2, and 3 and in FIGS. 78A (power vs. time) and 78B (energy
vs. time) for Control, CO2-4, 5, and 6.
TABLE-US-00025 TABLE 24 Compressive strengths, absolute (MPa) ID
Control CO2-1 CO2-2 CO2-3 CO2-4 CO2-5 CO2-6 12 hr 1.7 2.0 2.0 2.7
2.7 2.4 2.9 16 hr 5.9 6.4 6.0 6.5 6.8 6.0 6.5 24 hr 12.8 13.3 13.3
13.5 13.7 13.5 13.9 .sup. 7 d 31.5 31.7 31.3 33.1 32.9 32.6 33.1 28
d 37.3 37.9 38.7 38.0 38.9 38.7 39.1
TABLE-US-00026 TABLE 25 Compressive strengths, relative to
uncarbonated ID Control CO2-1 CO2-2 CO2-3 CO2-4 CO2-5 CO2-6 12 hr
100% 123% 119% 166% 163% 145% 174% 16 hr 100% 109% 103% 111% 116%
102% 110% 24 hr 100% 104% 104% 105% 107% 105% 109% .sup. 7 d 100%
101% 100% 105% 105% 104% 105% 28 d 100% 101% 104% 102% 104% 104%
105%
[0703] The set also slightly accelerated in highest CO.sub.2
dose.
[0704] The results show that in all cases, even at the lowest dose
of CO2 (0.05% CO2 delivered, bwc), there was an increase in early
strength. In general, the strength benefit of CO.sub.2 broadly
corresponded to increasing dose. The benefit was most pronounced at
the earliest ages, thought there was still a small benefit at 7 and
28 days.
[0705] This example demonstrates that very low doses of carbon
dioxide, added to concrete mixes after batching, cause marked
increases in early strength development. This was true even for the
lowest dose of carbon dioxide, 0.05%; at such low doses carbonation
of the concrete may not be detectable, but nonetheless the carbon
dioxide is acting in a manner similar to an admixture, in this case
as a potent accelerant of early strength development.
Example 29
[0706] This example is an illustration of low dose of gaseous and
solid carbon dioxide treatment of concrete in the drum of a ready
mix truck, from a liquid source of carbon dioxide, at a time
significantly after the batching of the concrete, and its effects
on early strength.
[0707] The 30 MPa slab mix design of Example 28 was used. 2 cubic
meters of concrete were produced, truck was less than half full.
Admixes added at test site TK-ADVA 140 superplasticizer 0.20% bwc,
sodium gluconate 0.05% bwc.
[0708] The CO.sub.2 supplied as a liquid, from a dewar with a hose
attached with a fitting on the end and an orifice of defined size,
5/64 inch. The dosing was calculated based on a series of
assumptions and is approximate. The assumptions were: 1) that the
carbon dioxide was 100% liquid in the line upstream of the orifice,
i.e., no phase 2 flow; 2) the flow was based on an equation (not
directly measured); and 3) that there was no pressure drop in the
line, that it was a constant 300 psi. The tube was directed into
the drum of the ready mix truck so as to deliver the gaseous and
solid carbon dioxide to the surface of the mixing concrete.
[0709] Table 26 shows the conditions for each sample. Staged dosing
was performed, with the first dose was delivered approximately 45
min after batching, and the final dose approximately 110 min after
batching. Thus, as with Example 28, dosing with CO.sub.2 was well
after mixing started, akin to supplying CO.sub.2 to a truck in
transit or at a job site rather than during batching.
TABLE-US-00027 TABLE 26 Conditions for each sample Sample ID
Control CO2-1 CO2-2 CO2-3 CO2-4 CO2-5 CO2-6 Time of Discharge 28 48
63 78 88 99 113 (min) Total CO.sub.2 Dose 0 0.10% 0.20% 0.30% 0.40%
0.50% 0.60% (% bwc) Temperature (.degree. C.) 19.5 20.7 20.8 21.2
21.5 22.3 23.2 Slump (inches) 7 4.5 3.75 4 3 2.75 2 Air Content (%)
1.8 -- -- -- -- -- 1.8 CO.sub.2 Uptake (% bwc) 0.00 -0.09 0.01
-0.01 0.01 0.07 0.10
[0710] 8-hr, 12-hour, 24-hour, 7-day, and 28-day strengths are
shown in Tables 27 (expressed as absolute strengths) and 28
(expressed as relative to uncarbonated control). Three specimens
were taken at each age as 4.times.8'' cylinders with reusable end
caps. Specimens were kept in moist curing storage until testing.
Calorimetry data is shown in FIGS. 79A (power vs. time) and 79B
(energy vs. time) for control, CO2-1, 2, and 3 and in FIGS. 80A
(power vs. time) and 80B (energy vs. time) for control, CO2-5 and
6.
TABLE-US-00028 TABLE 27 Compressive strengths, absolute (MPa)
Control CO2-1 CO2-2 CO2-3 CO2-4 CO2-5 CO2-6 8 hr 1.8 1.9 1.7 1.8
1.8 1.8 1.9 12 hr 6.1 6.4 6.1 6.4 6.3 6.8 7.0 24 hr 13.9 14.1 14.9
14.9 15.2 15.6 15.4 7 day 24.8 25.7 27.0 26.1 28.0 27.7 28.7 28 day
34.5 34.0 34.0 33.8 35.6 35.8 35.8
TABLE-US-00029 TABLE 28 Compressive strengths, relative to
uncarbonated Control CO2-1 CO2-2 CO2-3 CO2-4 CO2-5 CO2-6 8 hr 100%
107% 91% 97% 100% 98% 104% 12 hr 100% 104% 100% 105% 103% 112% 114%
24 hr 100% 101% 107% 108% 110% 113% 111% 7 day 100% 104% 109% 105%
113% 112% 116% 28 day 100% 99% 99% 98% 103% 104% 104%
[0711] Calorimetry shows that the carbonation treatment has
increased the heat release associated with the hydration of
aluminates, see FIGS. 79A, B and 80A, B, and Tables 27 and 28,
supporting the use of calorimetry as an alternative or additional
marker to strength measurements in determining desired or optimal
dosing conditions for carbonation of a concrete mix.
[0712] Strength benefit of CO.sub.2 broadly corresponded to
increasing dose. Set was slightly accelerated in highest CO.sub.2
dose.
[0713] This example demonstrates that dosing carbon dioxide into a
ready mix drum by using a liquid to solid/gas conversion as the
carbon dioxide is dosed is viable.
Example 30
[0714] This example is an illustration of low dose of gaseous and
solid carbon dioxide treatment of concrete in the drum of a ready
mix truck, from a liquid source of carbon dioxide, at a time
significantly after the batching of the concrete, and its effects
on early strength. The concrete mix included an SCM (slag). Two
trials were conducted on consecutive days. On the first day the
carbon dioxide was dosed at various times up to about 70 minutes
after batching. On the second day the carbon dioxide was dosed much
earlier after batching, at about 20 minutes.
[0715] One truck of 4 m.sup.3 of concrete was batched filled with a
25 MPa floor mix design, below:
TABLE-US-00030 Component Mass (kg/m.sup.3) Sand 959 Stone 1080
Cement 212 Slag 53 Water 155 SuperP (mL) 190
[0716] On the first day of the trial, one truck received three
serial doses of CO.sub.2 after the control sample. On the second
day of the trial, there was only one dose of CO.sub.2. The
injection of CO.sub.2 proceeded for 30-90 seconds with an
additional 90-180 seconds of high speed mixing after the injection
was completed. The requested load of concrete was first batched
into the truck before transport to the wash rack where the batch
received final water adjustments by the truck operator. Upon
completion of the batch adjustments a sample of uncarbonated
(control) concrete was removed, a slump test was performed, and
test specimens were cast. The truck was then subjected to three
sequential doses of carbon dioxide with assessment of slump and
casting of the treated concrete between each round. The time
between the start of mixing and the carbon dioxide application was
recorded. All of the test samples came from the same truck to
maximize the experimental results from a single batch and to
minimize any batch-to-batch variation that may have arisen. The
sequential dosing of carbon dioxide was pursued to determine an
optimum dose.
[0717] Whereas the trial of example 29 involved a tube held in
position, the trials from hereafter used a rigid injector tube. A
clamp allowed it to be fixed to the truck structure and held in
place. This type of system is similar to a portable system for
dosing carbon dioxide that could be mounted on the truck itself, so
that dosing can be done at any time before, during or after
batching, as a single dose or as staged doses.
[0718] Conditions are summarized in Table 29
TABLE-US-00031 TABLE 29 Conditions in trial Estimated Discharge
Total CO.sub.2 Truck Sample Time CO.sub.2 Dose Uptake Slump Temp
(day) Code Condition (min) (% bwc) (% bwc) (inches) (.degree. C.) 1
1401 Control 23 -- -- 3.5 23.9 1402 CO.sub.2 45 0.10% inconclusive
3.0 -- 1403 CO.sub.2 59 0.30% inconclusive 3.0 25.6 1404 CO.sub.2
74 0.60% inconclusive 2.0 26.5 2 1501 Control 10 -- -- 2.5 23.7
1502 CO.sub.2 20 0.30% inconclusive 2.0 24.9
[0719] Trials were run on two consecutive days. Compressive
strengths at 1, 3, 7, 28, and 56 for samples taken on the first day
are shown in FIGS. 81-85 and calorimetry for first-day samples is
shown in FIGS. 86A (power vs. time) and 86B (energy vs. time).
Three specimens were used for 1 day, two specimens at all other
ages. 4.times.8'' cylinders were subjected to end grinding to
create planar faces and kept in moist curing storage prior to
testing. For the second day, FIGS. 87-91 show strength at 1, 3, 7,
28, and 56 days and FIGS. 92A (power vs. time) and 92B (energy vs.
time) show calorimetry. It can be seen that for both days, shifts
in the calorimetry curves match the increases in strength, with the
greatest shift seen for the dose of carbon dioxide on a given day
that gave the greatest acceleration of strength development, see,
e.g., FIG. 86A. Three specimens were used for 1 day, two specimens
at all other ages. 4.times.8'' cylinders were subjected to end
grinding to create planar faces and kept in moist curing storage
prior to testing.
[0720] The carbon dioxide injection did not appear to have any
effect on the induction period. The acceleratory stage of hydration
for each sample was underway by 4 hours. By 7 hours the heat
evolution of the carbonated samples occurred at an increased rate
(as noted in a shift to the left of the shape of the curves) where
the effect was greater with the greater dose of carbon dioxide.
Further, the heat release at the peak of the early hydration was
found to increase in magnitude and be shifted to earlier times as
the carbon dioxide dose increased. An alternate interpretation of
the data considers the total energy released with time. The energy
release relative to the control can be quantified at various ages
and used as a metric of hydration progress. It is shown that at 6
hours the carbonated batches had released about 10% less energy
than the control. The low dose had matched the control by 11 hours
and remained equivalent thereafter. The second dose of CO.sub.2
reached 101% of the control at 9 hours before improving to 12%
better at 12 hours and finishing at 6% more energy released through
20 hours. The highest dose reached 102% of the control at 10 hours,
13% greater at 12 hours and 4% increase through 20 hours. It is
observed that the carbon dioxide may have slightly slowed the
hydration in the first 8 hours but in the 10 to 14 hour range an
accelerating effect could be realized in the two higher doses. This
potentially corresponds to a performance benefit such as a higher
strength at these times.
[0721] Resistance testing was also performed, following AASHTO TP
95-11 "Surface Resistivity Indication of Concrete's Ability to
Resist Chloride Ion Penetration" Electrical resistivity and
assessed risk of chloride penetration were measured.
[0722] Standards are summarized in Table 30, below.
TABLE-US-00032 TABLE 30 ASTM and AASTO standards AASHTO TP95-11
ASTM C1202 28 day Electrical 56 day RCPT Resistivity Chloride
Penetration Coulombs .OMEGA.m High >4000 <45.93 Moderate
2000-4000 45.93-91.86 Low 1000-2000 91.86-183.7 Very Low 100-1000
183.7 to 1837 Negligible <100 >1837
[0723] Results are summarized in Table 31.
TABLE-US-00033 TABLE 31 Resistivity results for carbonated
concretes Average Bulk Electrical Resistivity (.OMEGA.m) and
Chloride Penetration Risk for five test ages (days) Sample 1 3 7 28
56 1401 8.9 19.3 33.6 78.7 106.5 1402 8.8 18.9 25.5 74.1 112.0 1403
8.7 18.8 24.7 67.1 97.7 1404 8.9 20.3 24.1 70.2 101.8 1401 High
High High Moderate Low 1402 High High High Moderate Low 1403 High
High High Moderate Low 1404 High High High Moderate Low 1501 9.1
16.2 22.9 54.7 85.0 1502 8.9 16.1 22.0 50.8 82.8 1501 High High
High Moderate Moderate 1502 High High High Moderate Moderate
[0724] The CO.sub.2 treatment did not impact the resistivity with
values for the control & CO.sub.2 "moderate" at 28 days and
"low" at 56 days.
[0725] The use of staggered vs. single batch indicates that the
staggered batch (1403), when compared to the single dose (1502),
both at 0.30%, produced a more robust increase in strength. This
may be due to the batching, or it may be due to the time the carbon
dioxide was applied after mixing (60 min vs 20 min), or both. The
highest benefit was in the batch with the three-stage dose (1404),
with benefit from 13 to 26% across the test period. Calorimetry
results showed acceleration and greater energy release for the
staggered samples.
[0726] This example demonstrates that carbon dioxide at low doses
increases early strength with benefits maintained at later time
points, that the carbon dioxide did not affect resistivity, and
that the time after batching of carbon dioxide addition and/or
staging may affect the magnitude of the increase in early strength.
Finally, the Example illustrates the use of carbon dioxide in a mix
containing an SCM (slag), with beneficial results seen for the
carbonated vs. uncarbonated concrete.
Example 31
[0727] This example is a repeat of Example 30, with some
modifications. The same mix design was used (i.e., concrete with
SCM). One truck of 4 m.sup.3 of concrete received three serial
doses of CO.sub.2 after the control sample. The injection of
CO.sub.2 proceeded for 30-90 seconds with an additional 90-180
seconds of high speed mixing after the injection was completed. The
same carbon dioxide injection system as Example 30 was used. The
trial of Example 31 was a repeat of Example 30 to increase
confidence in the results. However, while delivering a CO.sub.2
injection to a truck stopped at the wash rack (as in Example 30) is
potentially feasible, breaking the delivery into multiple doses
represents a possible delay that is preferably avoided and is not
universally applicable. Many examples exists wherein concrete is
batched and mix centrally thereby precluding the need for a wash
rack and a related pause. Thus Example 31 included an alternate
CO.sub.2 injection mode (sample code 805, below) wherein the gas
was added during the initial batching/mixing phase.
[0728] The second truck had one dose of CO.sub.2, equivalent to two
doses of the first truck (0.30% carbon dioxide bwc) but was dosed
during mixing. Conditions for the samples in the trial are given in
Table 32.
TABLE-US-00034 TABLE 32 Conditions for samples Est Discharge Total
CO.sub.2 Sample Time CO.sub.2 Dose Uptake Slump Temp Truck Code
Condition (min) (% bwc) (% bwc) (inches) (.degree. C.) 1 801
Control 21 -- -- 3.5 22.4 802 CO.sub.2 30 0.10% inconclusive 3.0
24.0 803 CO.sub.2 46 0.30% inconclusive 2.5 24.7 804 CO.sub.2 55
0.60% inconclusive 1.5 27.3 2 805 CO2 -- 0.3% -- 3.0 23.3
[0729] Absolute compressive strengths are shown in Table 33 and
compressive strengths relative to uncarbonated control are shown in
Table 34. FIGS. 93A (power vs. time) and 93B (energy vs. time) show
calorimetry data for the various carbon dioxide doses.
TABLE-US-00035 TABLE 33 Compressive strengths, absolute Compressive
Strength (MPa) Control CO2 CO2 CO2 CO2 0801 0802 0803 0804 0805 1
day 8.0 8.0 8.6 8.7 9.2 3 day 14.8 15.8 16.6 16.1 18.6 7 day 19.2
20.4 21.4 22.1 23.2 28 day 30.8 32.0 33.9 32.8 35.5 56 day 32.8
27.9 37.9 36.4 38.7 91 day 36.9 38.4 39.1 39.5 42.5
TABLE-US-00036 TABLE 34 Compressive strengths, relative Strength
Relative to the Control Control CO2 CO2 CO2 CO2 0801 0802 0803 0804
0805 1 day 100% 99% 106% 108% 114% 3 day 100% 107% 112% 109% 126% 7
day 100% 106% 111% 115% 121% 28 day 100% 104% 110% 107% 115% 56 day
100% 85% 116% 111% 118% 91 day 100% 103% 106% 107% 115%
[0730] As in Example 30, when carbon dioxide was dosed in stages,
an increasing early (1 day) strength benefit was seen with
increasing dose, though the effect was not consistent at the later
time points. However, unlike Example 30, the single dose sample,
0805, was superior in strength at every time point to the same
dose, delivered in two stages (0803). In this Example, the single
dose was given during batching rather than after batching. This
method outperformed all of the staged doses at every time
point.
[0731] Calorimetry trends were consistent with Example 30, that is,
doses giving the greatest acceleration of strength also showed the
greatest shift in the calorimetry curves. The data considered as
energy shows the magnitude of the effect from the carbon dioxide.
The lowest dose released 20% more energy than the control through 2
hours. The benefit declined to 7% at 7 hours before increasing to
13% at 10 hours and thereafter the declining to be equivalent to
the control. The middle dose of CO.sub.2 was 41% higher than the
control at 2 hours with the benefit declining to 9% at 8 hours. The
energy release jumped to 16% ahead of the control at 10 hours
before declining to be equivalent to the control. For the highest
dose the energy was between 92% and 99% of the control in the first
9 hours before spiking to be 9% ahead and thereafter declining to
be equivalent to the control. It is evident that the lower doses of
CO.sub.2 had an effect on the very early hydration and all doses
had an effect notably around the 10 hour mark. The shape of the
power curves suggests that this time period is consistent with the
end of the acceleration period when the initial silicate hydration
starts to slow down.
[0732] The batch that was dosed with CO.sub.2 during batching (805)
showed a calorimetry response that appeared to show some
retardation relative to the control (data not shown). Heat
evolution was slower across the 7 to 13 hour interval. After
lagging to 83% of the control through 11 hours the hydration
accelerated and was 5% ahead at 15 hours thereafter increasing to
7% at 20 hours.
[0733] Bulk resistivity measurements were taken according to the
protocol used in Example 31. The results are shown in Table
34A.
TABLE-US-00037 TABLE 34A Bulk Resistivity (.OMEGA. m) and chloride
penetrability risk for test specimens at five different ages Sample
Code Condition 1 day 3 day 7 day 28 day 91 day 801 Control 9.6 14.9
21.0 58.3 123.4 802 0.1% CO.sub.2 9.6 16.4 21.6 56.8 122.2 803 0.3%
CO.sub.2 9.2 15.9 20.9 59.6 123.7 804 0.6% CO.sub.2 9.2 16.1 20.7
50.3 112.9 805 0.3% CO.sub.2 10.1 18.0 23.3 61.8 129.8 801 Control
High High High Moderate Low 802 0.1% CO.sub.2 High High High
Moderate Low 803 0.3% CO.sub.2 High High High Moderate Low 804 0.6%
CO.sub.2 High High High Moderate Low 805 0.3% CO.sub.2 High High
High Moderate Low
[0734] The bulk resistivity measurements were consistent with what
was observed in Example 31 insofar as the assessments of the
carbonated batches were equivalent to the control. The chloride
penetrability risk for all samples was assessed to be moderate at
28 days and low at 91 days.
[0735] This example confirms the consistent benefit of low dose
carbon dioxide on early strength development and demonstrates the
effect of time of carbon dioxide addition on the magnitude of the
strength benefit. The carbon dioxide addition during batching would
be equivalent of dosing done at the yard, whereas the other times
of carbon dioxide addition during the staged addition are akin to
dosing during transit and/or at the job site.
Example 32
[0736] In this example, carbon dioxide was added to concrete in
ready mix trucks almost immediately after batching, using the same
dose in two different trucks but different time for delivery of the
carbon dioxide. A mix design was used containing an SCM, in this
case, fly ash.
[0737] Three trucks were used, each 8.5 m.sup.3, thus these were
full trucks;
[0738] The mix design was: [0739] Sand 868 kg [0740] Stone 1050 kg
[0741] Cement 282 kg [0742] Fly ash 68 kg
[0743] CO.sub.2 was supplied as a liquid using a wand directing it
into the drum. In this Example the system would be equivalent to a
permanent system at the batching plant.
[0744] The CO.sub.2 was supplied to the concrete immediately after
the truck left the batch house. There was approximately 4 min of
batching/mixing in the house, 2 min reorientation of the truck, and
then the CO.sub.2 was added, as a single dose per truck. This would
be the equivalent of a dosing scheme at the batching plant. Only
one dose was given per truck, which was the same dose for each
truck but given over two different time periods. Conditions for the
trucks in the trial are given in Table 35.
TABLE-US-00038 TABLE 35 Conditions for samples in trial Total
CO.sub.2 Dose CO.sub.2 Uptake Slump Temp Truck Condition (% bwc) (%
bwc) (inches) (.degree. C.) 1 Control -- -- 5.5 21.1 2 CO.sub.2-1
0.50% over 4 min inconclusive 2.0 20.7 3 CO.sub.2-2 0.50% over 2
min inconclusive 6.0 21.6
[0745] Compressive strengths were measured at 1, 4, 7, and 28 days.
Absolute compressive strengths are given in Table 36; compressive
strengths relative to control are given in Table 37. Calorimetry
data is shown in FIGS. 94A (power vs. time) and 94B (energy vs.
time). Three specimens were used at all ages as 4.times.8''
cylinders with reusable end caps. Moist curing storage was used
prior to testing.
TABLE-US-00039 TABLE 36 Compressive strengths, absolute Compressive
Strength (MPa) Control CO2-1 CO2-2 1 day 15.2 18.9 14.2 4 day 31.4
33.4 28.3 7 day 31.7 37.6 33.1 28 day 44.9 47.8 42.0
TABLE-US-00040 TABLE 37 Compressive strengths, relative to control
Strength Relative to control Control CO2-1 CO2-2 1 day 100% 125%
93% 4 day 100% 107% 90% 7 day 100% 119% 105% 28 day 100% 106%
94%
[0746] The strength at every time point was superior in the
concrete from the truck dosed over 4 min (CO2-1) compared to the
truck dosed over 2 min (CO2-2), possibly because the slower
delivery allowed the fresh concrete more time to react without
swamping the system.
[0747] The example illustrates that another possibility for carbon
dioxide dosing can be after water is added to the mix and mixing
starts, but within minutes after mixing starts. In facilities with
a wash rack, where the truck is rinsed prior to departure and the
consistency of the concrete is checked, a truck may pause for about
ten minutes. This offers an opportunity for carbon dioxide dosing
in this time frame. This Example also illustrates the use of the
low dose carbon dioxide with a mix containing an SCM, and
beneficial results in early strength development compared to
uncarbonated control. Finally, this example further illustrates
that changes in calorimetry data correlate with early strength
changes.
Example 33
[0748] In this example, a method for screening a particular cement
to determine optimal carbon dioxide dosing was performed.
[0749] The mix design was Sand 1350 g, Cement 535 g, Water 267.5
g
[0750] The procedure was: [0751] Combine sand and water in kitchen
aid mixer--mix 30 s on setting #2 [0752] Add cement--mix 30 s on
setting #2 [0753] Remove uncarbonated sample for calorimetry and
CO.sub.2 analysis [0754] Carbonate for 2 minutes at 0.15 LPM [0755]
Remove sample #2 for calorimetry and CO.sub.2 analysis [0756]
Repeat steps 4 and 5 as many times as desired
[0757] In this example, Lafarge Brookfield cement was used, but the
procedure may be used for any cement to screen for optimal carbon
dioxide dosing.
[0758] An increase in heat released at early ages (acceleration)
was observed for all CO.sub.2 doses. Lower uptakes are better at
later ages; higher doses had negative impact on total energy. See
FIGS. 95-99. FIG. 95 shows calorimetry curves (power vs. time) for
5 mortars with varying levels of CO.sub.2 uptake (1 sample before
carbonation followed by 5 rounds of carbonation, each for 2 min at
0.15 LPM). FIGS. 96-99 give the results of the analysis of energy
released relative to the uncarbonated control at 4, 8, 12, and 16
hours.
[0759] This example illustrates a method for rapidly determining
optimal carbon dioxide dose for a particular cement to be used in,
e.g., a concrete mix, by using calorimetry as an alternative or
additional marker to strength development.
Example 34
[0760] In this example, delivery of CO.sub.2 via carbonated water
was tested with the carbonated water being used as the sole water
source for a concrete.
[0761] If some or all of the mix water in a wet mix concrete is
carbonated, it can contain an amount of CO.sub.2 that can be
sufficient to obtain a desired dose of carbon dioxide in the
concrete by the use of carbonated mix water alone, depending on the
desired dose; this is certainly true for many low dose mixes. For
example, consider a mix that is 350 kg/m.sup.3 of cement. A dose of
CO.sub.2 of 0.5% bwc would be 1.75 kg of CO.sub.2. At w/c of 0.45
there is 157.5 kg of water in a cubic meter. So a dose of CO.sub.2
of 0.5% would be 11.1 g CO.sub.2/L water. This amount of carbon
dioxide could be carried by carbonated water at about 94 psi and
25.degree. C. Cooler water could carry more, particularly if a
fraction of the water is to remain uncarbonated. Lower doses than
0.5% are easily achievable using carbonation of the mix water, or a
portion of the mix water.
[0762] Thus, we explored the use of carbonated water as a carrier
of the low dose of CO.sub.2.
[0763] Mix Procedure A--Control [0764] 1. Combine 1350 g sand and
53.5 g water in bowl--mix 30 s [0765] 2. Add 535 g cement to
bowl--mix 30 s [0766] 3. Add 214 g water to bowl over .about.10
s--mix 30 s [0767] 4. Mix mortar for additional 2 minutes
[0768] Mix Procedure B--CO.sub.2 [0769] 1. Combine 1350 g sand and
535 g cement in bowl--mix 30 s [0770] 2. Add 267.5 g carbonated
water to bowl--mix 30 s. Carbonated water was Perrier water. [0771]
3. Mix mortar for additional 2 minutes
[0772] In this trial, the mix water in the carbonated case was
added as one addition, and all of the mix water was carbonated.
[0773] Surprisingly, calorimetry indicated retardation of about 2
to 4 hours. See FIGS. 100 (power vs. time) and 101 (energy vs.
time). The time at which the carbonated mix water is introduced may
be important, and that a "pre wet" step before the carbonated water
addition can be used in order to "prime" the reactions in the
hydrating cement so that when the carbonated water is then added
the desired effect on strength acceleration is seen.
Example 35
[0774] In this example the effects of low dose carbonation on
reversing the retardation of early strength development in
concretes containing an SCM, in this case, fly ash, was
studied.
[0775] The procedure was as follows: [0776] Combine 1350 g sand and
267.5 g water in bowl--mix 30 s [0777] Add 428 g cement and 107 g
fly ash (80/20 blend)--mix 60 s [0778] Remove sample for
calorimetry and bakeoff [0779] Dose CO.sub.2 at 0.15 LPM for 2
minutes [0780] Remove sample for calorimetry and bakeoff [0781]
Dose CO.sub.2 at 0.15 LPM for 2 minutes (4 minutes total CO.sub.2
dose) [0782] Remove sample for calorimetry and bakeoff [0783] Dose
CO.sub.2 at 0.15 LPM for 2 minutes (6 minutes total CO2 dose)
[0784] Remove sample for calorimetry and bakeoff
[0785] Cements used in the trials were: Argos, Cemex, Holcim, Titan
Roanoake.
[0786] Fly ashes used in the trials were: Venture Belews creek,
SEFA Wateree.
[0787] The results are shown in FIGS. 102-109. In each Figure, the
CO.sub.2 uptake for the particular mix is given for the three
different carbon dioxide doses, and calorimetry, reported as total
energy released at a discrete time interval (8, 16, and 23 hours
after mixing) is shown, as a percent of uncarbonated control. FIG.
102 shows results for an Argos cement+Venture FA mix. FIG. 103
shows results for a Cemex cement+Venture FA mix. FIG. 104 shows
results for a Holcim cement+Venture FA mix. FIG. 105 shows results
for a Titan Roanoake cement+Venture FA mix. FIG. 106 shows results
for an Argos cement+SEFA FA mix. FIG. 107 shows results for a Cemex
cement+SEFA FA mix. FIG. 108 shows results for a Holcim cement+SEFA
FA mix. FIG. 109 shows results for a Titan Roanoake cement+SEFA FA
mix. In summary, for Venture ash: In all four cements an increased
heat of hydration release was observed at 8 and 16 hours. Generally
equivalent at 23 hours. For SEFA ash: Observed similar effect as
Venture ash in 3 cements. Holcim was behind at the early ages and
equivalent at 23 hours.
[0788] The greater energy release detected by calorimetry in the
carbonated samples indicates probable early strength increase. This
is important in SCM mixes, because producers in many markets stop
using fly ash or slag during colder weather due to slower strength
development.
[0789] Greater strength increases for the carbonated batches allows
producers to use fly ash or slag in colder weather when slower
strength development associated with SCMs would otherwise cause
them to opt against using fly ash or slag.
[0790] This example demonstrates the use of low dose carbonation to
accelerate strength development in concrete mixes utilizing an SCM,
thus potentially partially or completely offsetting the retardation
of strength development seen in these mixes when they are not
carbonated.
Example 36
[0791] In this example the effects of low dose carbonation on
reversing the retardation of early strength development in
concretes containing an SCM, in this case, fly ash, was further
studied.
[0792] One fly ash was used, Class F Trenton fly ash. Two ordinary
portland cements were used, St Mary's Bowmanville (STMB) and
Roanoake. The blend fraction was 80% cement, 20% fly ash
[0793] The procedure was as follows: [0794] Combine 1350 g of sand
and 267.5 g of water in bowl and for mix 30 s [0795] Add 428 g of
cement 107 g of fly ash and mix for 30 s [0796] For carbonated
mortar, mix an additional 2, 4 or 6 minutes with a CO.sub.2 flow
rate of 0.15 LPM [0797] For control mortar mix an additional 4
minutes [0798] Cast samples
[0799] The batch was then sampled and calorimetry performed as
described herein. Values derived from calorimetry were used as an
alternative marker to strength development, also as described
herein.
[0800] The calorimetry results for the Roanoake-Trenton blend are
shown in FIGS. 110 (power) and 111 (energy) and in Table 38 (energy
relative to control). The results for STMB cement are shown in
FIGS. 112 (power) and 113 (energy) and in Table 39 (energy relative
to control).
TABLE-US-00041 TABLE 38 Energy, via calorimetry, relative to
control at specific time intervals for an 80/20 blend of Roanoake
cement and Trenton fly ash Time After CO.sub.2 CO.sub.2 CO.sub.2
Mixing (h) Control 2 min 4 min 6 min 1 -- -- -- -- 2 100% 49% 73%
67% 3 100% 74% 95% 86% 4 100% 90% 113% 99% 5 100% 103% 126% 107% 6
100% 112% 130% 109% 7 100% 117% 130% 107% 8 100% 120% 127% 105% 9
100% 121% 125% 102% 10 100% 121% 122% 100% 11 100% 120% 120% 99% 12
100% 120% 117% 98% 13 100% 119% 114% 97% 14 100% 117% 112% 96% 15
100% 116% 110% 96% 16 100% 115% 108% 96% 17 100% 114% 107% 96% 18
100% 114% 106% 96% 19 100% 113% 105% 96% 20 100% 112% 104% 96% 21
100% 112% 104% 96% 22 100% 112% 103% 96% 23 100% 111% 103% 96% 24
100% 111% 102% 97%
TABLE-US-00042 TABLE 39 Energy, via calorimetry, relative to
control at specific time intervals for an 80/20 blend of St Mary's
Bowmanville cement and Trenton fly ash Time After CO.sub.2 CO.sub.2
CO.sub.2 Mixing (h) Control 2 min 4 min 6 min 1 -- -- -- -- 2 100%
80% 68% 48% 3 100% 83% 81% 73% 4 100% 88% 88% 83% 5 100% 94% 93%
89% 6 100% 98% 95% 91% 7 100% 100% 95% 90% 8 100% 101% 94% 88% 9
100% 101% 92% 87% 10 100% 101% 92% 86% 11 100% 100% 91% 85% 12 100%
100% 91% 85% 13 100% 99% 90% 84% 14 100% 99% 90% 83% 15 100% 98%
89% 83% 16 100% 98% 89% 82% 17 100% 97% 89% 82% 18 100% 97% 89% 82%
19 100% 96% 89% 82% 20 100% 96% 89% 82% 21 100% 96% 89% 82% 22 100%
95% 89% 82% 23 100% 95% 89% 82% 24 100% 95% 89% 82%
[0801] There was strong acceleration observed in the
Roanoake-Trenton blend. The 2 min dose (0.06% bwc CO.sub.2 uptake)
saw more energy released than the control at ages beyond 5 hours,
with at least 20% more energy observed through the interval of 8 to
12 hours. Total energy released at 24 hours was 111% of the
control. The 4 min dose (0.26% bwc CO.sub.2 uptake) saw more energy
released than the control at all times greater than 4 hours with
the benefit exceeding 10% from 6 hours to 15 hours. The maximum
reached 30% more at 6 to 7 hours. Total energy released at 24 hours
was 102% of the control. The 6 min dose (0.38% bwc CO.sub.2 uptake)
released slightly more energy that the control through the ages 5
to 9 hours (max 9% ahead at 6 hours). Total energy released at 24
hours was 97% of the control.
[0802] In contrast, there was no acceleration observed in the St
Mary's-Trenton blend. The 2 min dose (0.14% bwc CO.sub.2 uptake)
saw less energy released than the control at all ages except the
interval of 7 to 12 hours when it was equivalent. Total energy
released at 24 hours was 95% of the control. The 4 min dose (0.27%
bwc CO.sub.2 uptake) saw less energy released than the control at
all ages. The maximum was 95% in the interval of 6 to 7 hours.
Total energy released at 24 hours was 89% of the control. The 6 min
dose (0.48% bwc CO.sub.2 uptake) saw less energy released than the
control at all ages. The maximum was 91% at 6 hours. Total energy
released at 24 hours was 82% of the control.
[0803] This Example is a further demonstration of the effects of
mix type on the carbonation results, with markedly different
results being obtained depending on the cement used in the
mix--virtually no effect of carbonation in the STMB-Trenton mix,
and a pronounced effect in the Roanoke-Trenton mix. The effect of
carbonation in a given mix is best studied in that mix; this may be
especially important in cement/SCM blends, in which both the
specific type of cement and the specific type of SCM may contribute
reactive species that influence the course and/or effect of
carbonation. This Example also illustrates that, with the proper
cement/SCM mix, carbonation of the mix, e.g., with low doses of
carbon dioxide, can accelerate the development of early strength,
as indicated by calorimetry; in some cases the acceleration can be
quite marked, even at a relatively low dose of carbon dioxide.
Finally, a given mix may demonstrate different time courses of
acceleration of strength development; this can be useful in certain
field conditions when a particular operation is desired to be
carried out at a particular time after the mix is poured, e.g.,
removal of molds, finishing, and the like, which require a certain
strength of the concrete. Earlier times of accelerated strength
development could be desired to, e.g., shorten the time that the
concrete is in the mold, while later times of accelerated strength
development could be desired to, e.g., allow concrete finishing to
occur earlier.
Example 37
[0804] In this Example the use of bicarbonate as a source of
carbonate in the carbonation of cement mixes was studied.
[0805] As described elsewhere herein, and without being bound by
theory, the relevant reactions in carbonation of cement mixes or
other mixes containing the requisite reactive species are: [0806]
1. Dissolution of gas in water to form dissolved carbon
dioxide:
[0806] CO.sub.2(g).fwdarw.CO.sub.2(solution) [0807] 2. Reaction of
dissolved carbon dioxide with water to form carbonic acid:
[0807] H.sub.2O+CO.sub.2(solution).fwdarw.H.sub.2CO.sub.3(aq)
[0808] 3. Reaction of carbonic acid with hydroxide or other base to
form bicarbonate:
[0808]
H.sub.2CO.sub.3(aq)+OH.sup.-(aq).fwdarw.HCO.sub.3.sup.-(aq)+H.sub-
.2O(l) [0809] 4. Reaction of bicarbonate with hydroxide or other
base to form carbonate:
[0809]
HCO.sub.3.sup.-(aq)+OH.sup.-(aq).fwdarw.CO.sub.3.sup.2-(aq)+H.sub-
.2O(l) [0810] 5. Reaction of carbonate with calcium (or alternative
ion) to form solid carbonate:
[0810] CO.sub.3.sup.2-(aq)+Ca.sup.2+(aq)CaCO.sub.3(s)
[0811] There are a number of points where the conditions under
which the reactions are taking place can affect various steps in
the carbonation. The dissolution of carbon dioxide in water, 1, is
affected by temperature, the presence or absence of catalysts, and
other factors. Similarly, the formation of carbonic acid, 2, is
affected by the pH of the water, etc., as is the reaction of
carbonic acid with hydroxide or other base to form bicarbonate, 3.
The base for the reaction of 3 need not be a strong base, as the
pK.sub.a for this reaction is relatively low, around 7 or so, so
that the reaction could be occurring even in the mix water in
embodiments in which carbon dioxide is added to the mix water. The
processes of 1 and 2 may be circumvented by using carbon
dioxide-charged water (e.g., mix water) in a test; depending on the
pH of the mix water, process 3 may also be partially or completely
circumvented as well. The use of bicarbonate solution does
circumvent all of processes 1, 2, and 3, allowing just carbonation
of the cement mix to be tested.
[0812] In the present Example, a bicarbonate solution is used as a
source of substrate to be converted o carbonate in tests of
carbonation of cement mixes. By removing the variables associated
with dissolution and conversion to carbonic acid and bicarbonate,
just the effects of the cement and other reactive components of the
mix may be analyzed, to get a rapid and accurate picture of cement
and other effects alone. It is possible to determine whether or not
carbonation is effective with a given cement or cement mix, and to
determine the optimum or desired level of carbonation to be
achieved, since all or substantially all of the bicarbonate is
converted to carbonate in the reactions in the mixing cement mix.
The effects of various doses on the timing of strength increase can
also be observed. In this way, the focus in the field can be
shifted to achieving the desired carbonation, given the conditions
of mix water, mix time, timing of batch operations, source of
carbon dioxide, potential feedback control, and the like, to
achieve consistent and efficient carbonation in the field. Lab
results can be used in preliminary field test to confirm the
carbonation dose and to demonstrate the effectiveness of
carbonation, before relying on delivery of carbon dioxide to the
cement mix in the field.
[0813] Where one CO.sub.2 molecule forms a single bicarbonate
molecule, an effective CO.sub.2 dose as sodium bicarbonate can be
calculated as follows: [0814] CO.sub.2 (as bicarb)=(dose
CO.sub.2)*(Molar Mass Sodium Bicarbonate/Molar Mass CO.sub.2)
[0815] Thus: CO.sub.2 (as bicarb)=(dose CO.sub.2)*(84/44)=(dose
CO.sub.2)*1.91 [0816] For example, a 0.10% bwc CO.sub.2 dose would
require a 0.191% bwc dose of sodium bicarbonate
[0817] Two different cements were used in the tests, Lafarge
Brookfield (LAFB) and St Mary's Bowmanville (STMB), with the batch
plan shown in Table 40
TABLE-US-00043 TABLE 40 Dosage plan for bicarbonate testing Mass
Mass Dosage Equivalent Total Cement Water 1 Water 2 NaHCO.sub.3
NAHCO.sub.3 CO.sub.2 dose Water Mass Batch (g) (g) (g) (g) (% bwc)
(bwc) (g) 1 535 53.5 250 0 -- -- 303.5 2 535 53.5 250 0.5 0.09%
0.05% 303.5 3 535 53.5 250 1.0 0.18% 0.10% 303.5 4 535 53.5 250 2.0
0.37% 0.20% 303.5
[0818] The mix procedure was as follows:
[0819] Add sodium bicarbonate (NaHCO.sub.3) into water 2 and stir
thoroughly to dissolve
[0820] Combine sand and water 1 (10% of cement mass) in bowl and
mix 30 s
[0821] Add cement to bowl and mix 30 s
[0822] Add water 2 over designated timeframe (4 minutes)
[0823] Mix an additional 30 s
[0824] The batch was then sampled and calorimetry performed as
described herein. Values derived from calorimetry were used as an
alternative marker to strength development, also as described
herein.
[0825] The results for STMB cement are shown in FIGS. 114 (power)
and 115 (energy) and in Table 41 (energy relative to control). The
results for LAFB cement are shown in FIGS. 116 (power) and 117
(energy) and in Table 42 (energy relative to control).
TABLE-US-00044 TABLE 41 Energy, via calorimetry, relative to
control at specific time intervals for STMB cement mixed with
sodium bicarbonate Time After 0.09% 0.18% 0.37% Mixing (h) Control
bicarb bicarb bicarb 1 -- -- -- -- 2 100% 95% 116% 100% 3 100% 99%
104% 102% 4 100% 101% 104% 102% 5 100% 103% 104% 101% 6 100% 103%
103% 98% 7 100% 103% 103% 97% 8 100% 103% 102% 95% 9 100% 103% 101%
94% 10 100% 103% 101% 94% 11 100% 103% 101% 94% 12 100% 103% 101%
94% 13 100% 103% 101% 94% 14 100% 103% 101% 94% 15 100% 103% 101%
94%
TABLE-US-00045 TABLE 42 Energy, via calorimetry, relative to
control at specific time intervals for LAFB cement mixed with
sodium bicarbonate Time After 0.09% 0.18% 0.37% Mixing (h) Control
bicarb bicarb bicarb 1 -- -- -- -- 2 100% 92% 141% 163% 3 100% 95%
133% 155% 4 100% 103% 134% 151% 5 100% 107% 130% 140% 6 100% 109%
123% 129% 7 100% 108% 116% 120% 8 100% 106% 110% 112% 9 100% 105%
106% 107% 10 100% 104% 103% 104% 11 100% 103% 100% 101% 12 100%
102% 98% 98% 13 100% 100% 96% 96% 14 100% 99% 94% 95% 15 100% 99%
93% 94% 16 100% 98% 92% 93% 17 100% 98% 92% 92% 18 100% 97% 91% 91%
19 100% 97% 90% 91% 20 100% 96% 90% 90%
[0826] The results confirm those of previous Examples that show
that the effects of carbonation are highly dependent on cement type
used. In the batches in which STMB cement was used, the bicarbonate
had almost no effect on the calorimetry, at any dose, whereas in
the LAFB batches, carbonation at all doses caused an increase in
early hydration, similar to Example 33, with the effect being
dose-dependent. 2.0 g of bicarbonate was the best of three doses
with a 63% increase in energy at two hours gradually declining to
12% at 8 hours.
[0827] This Example demonstrates the use of bicarbonate in testing
of carbonation of different cement mixes, in order to examine
effects of carbonation alone, without dissolution and early
reaction effects, and demonstrates that different cements react
differently to carbonation. The results of the use of bicarbonate
with the LAFB and STMB cements were in agreement with results from
carbonation using carbon dioxide with these cements, confirming
that bicarbonate can be used as a carbonation testing tool.
Example 38
[0828] In this Example, carbonated mix water was used as the source
of carbon dioxide for carbonation of cement mixes, and the effects
of delaying the addition of the carbonated mix water, or duration
of addition of the carbonated mix water were tested.
[0829] In a first test, carbonated mix water was added at the
beginning of mixing or after a short delay. This allows the testing
to concern itself with timing of the CO.sub.2 in the mixing process
rather than with a gas-to-solution reaction, i.e., to circumvent
reactions 1 and 2 shown in Example 37 Carbonated water was
Perrier.
[0830] The mix procedure was as follows: [0831] Combine sand, tap
water 1 (53.5 g), carbonated water 1 (either no carbonation or
carbonated) and cement in bowl--mix 60 s [0832] Add both tap water
2 and carbonated water 2 (carbonated) to bowl over 10 s--mix 60 s
[0833] Mix mortar for an additional 1 min [0834] Cast for strength,
CO.sub.2 and calorimetry
[0835] The batch plan was as shown in Table 43.
TABLE-US-00046 TABLE 43 Carbonated timing work batches Tap Carb Tap
Carb. Total Cement Water 1 Water 1 Water 2 Water 2 pre- Batch (g)
(g) (g) (g) (g) wet 1 535 267.5 0 0 0 267.5 2 535 53.5 0 214 0 53.5
3 535 53.5 214 0 0 267.5 4 535 53.5 0 0 214 53.5
[0836] The batch was then sampled and calorimetry performed as
described herein. Values derived from calorimetry were used, also
as described herein.
[0837] The results for STMB cement are shown in FIGS. 118 (power)
and 119 (energy) and in Table 44 (energy relative to control). The
results for LAFB cement are shown in FIGS. 120 (power) and 121
(energy) and in Table 45 (energy relative to control).
TABLE-US-00047 TABLE 44 Energy, via calorimetry, relative to
control at specific time intervals for STMB cement subjected to
different mix water compositions and timings. Time After Control -
CO2 CO2 - Mixing (h) Control split water up front split water 2
100% 94% 0% 134% 3 100% 103% 37% 122% 4 100% 103% 46% 124% 5 100%
103% 54% 125% 6 100% 103% 62% 123% 7 100% 103% 70% 119% 8 100% 103%
76% 116% 9 100% 103% 81% 112% 10 100% 103% 85% 110% 11 100% 103%
88% 108% 12 100% 103% 90% 106% 13 100% 103% 91% 104% 14 100% 103%
92% 103% 15 100% 103% 93% 101% 16 100% 103% 93% 100% 17 100% 103%
94% 99% 18 100% 103% 94% 98% 19 100% 103% 94% 97%
TABLE-US-00048 TABLE 45 Energy, via calorimetry, relative to
control at specific time intervals for LAFB cement subjected to
different mix water compositions and timings. Time After Control -
CO2 CO2 - Mixing (h) Control split water up front split water 2
100% 227% 0% 41% 3 100% 137% 51% 94% 4 100% 122% 53% 107% 5 100%
117% 65% 115% 6 100% 114% 75% 115% 7 100% 112% 82% 111% 8 100% 110%
88% 107% 9 100% 109% 92% 104% 10 100% 108% 95% 102% 11 100% 107%
98% 100% 12 100% 107% 101% 98% 13 100% 106% 103% 97% 14 100% 106%
104% 96% 15 100% 106% 105% 95% 16 100% 106% 106% 95% 17 100% 106%
107% 95% 18 100% 106% 107% 95% 19 100% 106% 108% 95% 20 100% 106%
108% 95% 21 100% 106% 108% 95% 22 100% 106% 108% 94% 23 100% 106%
108% 94%
[0838] For the STMB cement, the addition of carbonated water as
part of the mix water showed a retardation up to 10 hours (less
than 85% of the energy released by the control) before reaching 93%
of the energy released by the control at ages greater than 15
hours. In contrast, the delayed addition of the same amount of mix
water showed that energy release was more than 15% ahead of the
control through the first 8 hours of hydration before being
equivalent to the control after 15 hours. There was no appreciable
difference in the uncarbonated system whether the water was added
all at once or in an 80/20 split.
[0839] For the LAFB cement the addition of carbonated water as part
of the mix water showed a retardation across the first 7 hours
(wherein less than 85% of the energy released by the control)
before reaching an 8% increase in energy released versus the
control at ages greater than 19 hours. For the delayed addition of
the same amount of carbonated water the hydration energy release
was more than 15% ahead of the control by the 5.sup.th and 6.sup.th
hours of hydration before being slightly behind the control after
15 hours. In this case, the 80/20 split addition of uncarbonated
mix water showed a marked acceleration at early time points, as
compared to the all at once addition.
[0840] These results demonstrate again that results vary depending
on the cement used. Both the STMB and the LAFB showed a marked
retardation of hydration, as shown by calorimetry, when the
carbonated mix water was added without a delay; however, the LAFB
cement had recovered and even accelerated hydration by 12 hours,
whereas the STMB did not recover in the 23 hours tested. In both
STMB and LAFB, delaying the addition of the carbonated mix water
resulted in acceleration of hydration, but at different times and
to different degrees. For STMB, there was marked acceleration at
the first hour time point, continuing to 15 hours. In contrast, the
acceleration of hydration in the LAFB system was not apparent until
4 hours and ended by 11 hours, and was moderate compared to that of
STMB.
[0841] In a second test, the delay until addition of carbonated
water and the amount of carbonated water were kept constant, and
the overall duration of addition of the water was varied. LAFB
cement was used. The carbonated water was Perrier. The mix
procedure was as follows:
[0842] Combine sand and water 1 in bowl--mix 30 s
[0843] Add cement to bowl--mix 30 s
[0844] Add both water 2 and carbonated water over designated
timeframe (2-5 minutes)
[0845] Mix mortar for total of 2 minutes
[0846] Note for batches 4 and 5 the total mix time was 5
minutes
[0847] The batch plan was as shown in Table 46.
TABLE-US-00049 TABLE 46 Batch plan for various durations for
addition of carbonated water. Mass Carbonated Total Cement Water 1
water Dose Water Mass Addition Batch (g) (g) (g) (g) time 1 535
53.5 250 303.5 30 seconds 2 535 53.5 250 303.5 60 seconds 3 535
53.5 250 303.5 120 seconds 4 535 53.5 250 303.5 180 seconds 5 535
53.5 250 303.5 300 seconds
[0848] The calorimetry results are shown in FIGS. 122 (power) and
123 (energy) and in Table 47 (energy relative to control).
TABLE-US-00050 TABLE 47 Energy, via calorimetry, relative to
control at specific time intervals for LAFB cement with different
durations of time for carbonated water addition Time After Mixing
(h) 0.5 min 1 min 2 min 3 min 5 min 1 -- -- -- -- -- 2 -- -- -- --
-- 3 100% 109% 122% 186% 228% 4 100% 117% 141% 192% 229% 5 100%
116% 137% 166% 191% 6 100% 111% 125% 140% 156% 7 100% 107% 117%
124% 135% 8 100% 104% 112% 114% 122% 9 100% 102% 109% 108% 114% 10
100% 101% 107% 104% 109% 11 100% 101% 106% 102% 106% 12 100% 100%
105% 100% 104% 13 100% 100% 104% 99% 102% 14 100% 99% 104% 98% 101%
15 100% 99% 103% 97% 100% 16 100% 99% 103% 97% 100% 17 100% 99%
102% 97% 99%
[0849] As compared to the quickest addition of carbonated water,
the slower the addition the greater the benefit. Benefits were
observed mostly in hydration periods up to 9 hours after
mixing.
[0850] This Example demonstrates that varying the duration of
addition of carbonated mix water to a cement mix can have marked
effects on early hydration.
Example 39
[0851] In this Example, carbonated mix water was derived from
artificial wash water and used as the source of carbon dioxide for
carbonation of cement mixes.
[0852] In concrete production, process water is produced in various
stages of the production and packaging process, such as truck
cleanout and other processes, where the process water has a high pH
that can be necessary to reduce before the water can be discharged.
Current treatment methods include the use of HCl, but the process
is difficult to control and has safety issues involved with
handling a concentrated acid. An alternative method utilizes carbon
dioxide addition to the process water. The carbon dioxide forms
carbonic acid, a weak acid, that is converted to bicarbonate and
ultimately carbonate (e.g., calcium carbonate). As the pH is
lowered by these reactions, it eventually reaches 7 or 8, and the
precipitated calcium carbonate dissolves, creating calcium
bicarbonate. Because of the pKas of the various reactions, the
system is buffered and it is easier to achieve the desired pH for
discharge. Thus, certain embodiments provide treatment of process
water from a manufacturing process that produces high-pH process
water, such as concrete manufacture, with carbon dioxide, such as
carbon dioxide produced in lime and/or cement manufacture to lower
the pH of the process water. This Example tests whether the
carbonated wash water could then be used as mix water in the
concrete batching process.
[0853] The following procedure was used: [0854] A synthetic "wash
water" was prepared by mixing a 2% cement by weight solution with
0.20% bwc sodium gluconate, in water. The gluconate was added since
the addition of a retarder is a conventional part of the wash
process to prevent the concrete from setting up in the ready-mix
truck prior to washing. [0855] The mixture was shaken periodically
and allowed to sit for 24 hr. [0856] Combine sand (1350 g) and
water 1--mix 30 s [0857] Add cement (STMB, 535 g)--mix 30 s [0858]
Add both water 2 and wash water to bowl--mix 2 minutes [0859] Cast
samples
[0860] The testing compared unfiltered vs filtered wash water, in
both uncarbonated and carbonated variations. Wash water was
carbonated by treating it in a home soda making device according to
the manufacturer's instructions to make carbonated water. The wash
water was filtered through filter paper to remove suspended solids.
Batching is shown in Table 48. The carbonated wash water
represented over 60% of the total water used in the cement
mixes.
TABLE-US-00051 TABLE 48 Carbonated wash water work batches Wash
Total Cement Water 1 Water Water 2 Water Wash Batch (g) (g) (g) (g)
(g) water 1 535 53.5 171.2 42.8 267.5 Filtered, uncarbonated 2 535
53.5 171.2 42.8 267.5 Filtered, carbonated 5 535 53.5 171.2 42.8
267.5 Unfiltered, uncarbonated 6 535 53.5 171.2 42.8 267.5
Unfiltered, carbonated
[0861] The calorimetry results are shown in FIGS. 123 (power) and
124 (energy) and in Tables 49 (unfiltered) and 50 (filtered).
TABLE-US-00052 TABLE 49 Energy, via calorimetry, relative to
uncarbonated control at specific time intervals for STMB cement
with filtered simulated wash water used as 80% of the mix water
Time After Filtered, Filtered, Mixing (h) uncarbonated carbonated 2
100% 194% 3 100% 110% 4 100% 111% 5 100% 109% 6 100% 109% 7 100%
108% 8 100% 107% 9 100% 105% 10 100% 103% 11 100% 102% 12 100% 101%
13 100% 100% 14 100% 99% 15 100% 98% 16 100% 96% 17 100% 96% 18
100% 95%
TABLE-US-00053 TABLE 50 Energy, via calorimetry, relative to
uncarbonated control at specific time intervals for STMB cement
with unfiltered simulated wash water used as 80% of the mix water
Time After Unfiltered, Unfiltered, Mixing (h) uncarbonated
carbonated 2 100% 28% 3 100% 62% 4 100% 77% 5 100% 88% 6 100% 95% 7
100% 99% 8 100% 101% 9 100% 102% 10 100% 103% 11 100% 103% 12 100%
104% 13 100% 103% 14 100% 103% 15 100% 103% 16 100% 102% 17 100%
102% 18 100% 102%
[0862] When the wash water was filtered the carbonation treatment
resulted in some early hydration acceleration (94% more energy
released through 2 hours, 10% through 3 hours, 11% through 4 hours)
before trending downwards to be 8% lower at 22 hours. When the wash
water was unfiltered the carbonation treatment resulted in early
hydration retardation (not until 6 hours was the energy within 10%
of the control) before the energy release became comparable to the
control.
[0863] This Example illustrates that carbonated wash water can be
used as part or all of the mix water in a cement mix with
acceleration of hydration in the subsequent mix compared to
uncarbonated control. The use of carbonated wash water can allow
the simultaneous treatment of the wash water, its disposal in a
cement mix, and a beneficial or at least neutral effect on the
subsequent mix. If the carbon dioxide comes from the cement making
process itself, it also represents an avenue for decreasing the
carbon footprint of the overall cement process.
Example 40
[0864] In this Example, the effect of carbonation on early
hydration was tested for two different low temperature
conditions.
[0865] Industrially produced concrete can vary in temperature, both
at the batching facility and at the job site. Typically, a concrete
mix is required to be between 10-30.degree. C. at time of delivery,
though it can potentially be hotter or colder at time of
batching
[0866] In this test, a series of mortar samples were carbonated at
low temperatures to observe if the effect of CO.sub.2 on cement was
sensitive to mix temperature. Two temperature ranges were used, 5
to 10.degree. C. and 10 to 15.degree. C. Isothermal calorimetry was
performed in the same temperature range as mixing.
[0867] The procedure was as follows: [0868] Combine 1350 g of sand
and 267.5 g of water in bowl and for mix 30 s [0869] Add 535 g of
cement and mix for 30 s [0870] For carbonated mortar, mix an
additional 2, 4 or 6 minutes with a CO.sub.2 flow rate of 0.15 LPM
[0871] For control mortar mix an additional 4 minutes [0872] Cast
samples
[0873] Two ordinary portland cements were used: St Mary's
Bowmanville (STMB) or Lafarge Brookfield (LAFB)
[0874] For LAFB cement mortars, FIGS. 125 and 126 show power and
energy curves, respectively at 5 to 10.degree. C., and FIGS. 127
and 128 and show power and energy curves, respectively at 10 to
15.degree. C., while Table 51 shows summary of energy compared to
control system at 5 to 10.degree. C. and Table 52 shows summary of
energy compared to control system at 10 to 15.degree. C.
TABLE-US-00054 TABLE 51 Energy, via calorimetry, relative to
control at specific time intervals for LAFB cement hydrated at a
temperature between 5 and 10.degree. C. Time After Control CO2 CO2
CO2 Mixing (h) 5.degree. C. 2 min 4 min 6 min 1 -- -- -- -- 2 100%
80% 45% 22% 3 100% 73% 46% 38% 4 100% 73% 40% 35% 5 100% 75% 45%
41% 6 100% 78% 57% 53% 7 100% 80% 69% 64% 8 100% 83% 79% 74% 9 100%
85% 86% 81% 10 100% 88% 92% 86% 11 100% 89% 95% 90% 12 100% 90% 99%
93% 13 100% 91% 102% 96% 14 100% 92% 104% 98% 15 100% 93% 106% 100%
16 100% 93% 107% 101% 17 100% 94% 109% 102% 18 100% 94% 110% 103%
19 100% 94% 110% 103% 20 100% 94% 111% 104% 21 100% 95% 111% 104%
22 100% 95% -- -- 23 -- -- -- -- 24 -- -- -- --
TABLE-US-00055 TABLE 51 Energy, via calorimetry, relative to
control at specific time intervals for LAFB cement hydrated at a
temperature between 10 and 15.degree. C. Time After Control CO2 CO2
CO2 Mixing (h) 10.degree. C. 2 min 4 min 6 min 1 100% 106% 160% 0%
2 100% 84% 108% 36% 3 100% 82% 95% 73% 4 100% 89% 102% 97% 5 100%
95% 107% 107% 6 100% 97% 107% 107% 7 100% 99% 105% 104% 8 100% 100%
102% 100% 9 100% 100% 101% 98% 10 100% 100% 99% 95% 11 100% 100%
97% 93% 12 100% 100% 95% 91% 13 100% 100% 94% 89% 14 100% 99% 92%
88% 15 100% 99% 92% 87% 16 100% 99% 91% 86% 17 100% 99% 90% 86% 18
100% 98% 90% 85% 19 100% 98% 89% 85% 20 100% 98% 89% 84% 21 100%
98% 88% 84% 22 100% 98% 88% 84% 23 100% 97% 88% 83% 24 100% 97% 87%
--
[0875] For STMB cement mortars, FIGS. 129 and 130 show power and
energy curves, respectively at 5 to 10.degree. C., and FIGS. 131
and 132 and show power and energy curves, respectively at 10 to
15.degree. C., while Table 53 shows summary of energy compared to
control system at 5 to 10.degree. C. and Table 54 shows summary of
energy compared to control system at 10 to 15.degree. C.
TABLE-US-00056 TABLE 53 Energy, via calorimetry, relative to
control at specific time intervals for STMB cement hydrated at a
temperature between 5 and 10.degree. C. Time After Control CO2 CO2
CO2 Mixing (h) 5.degree. C. 2 min 4 min 6 min 1 -- -- -- -- 2 100%
62% 67% 76% 3 100% 56% 64% 68% 4 100% 57% 67% 74% 5 100% 60% 72%
83% 6 100% 64% 78% 91% 7 100% 68% 83% 97% 8 100% 72% 88% 100% 9
100% 75% 91% 102% 10 100% 79% 93% 103% 11 100% 82% 95% 103% 12 100%
84% 96% 103% 13 100% 86% 97% 102% 14 100% 88% 98% 102% 15 100% 89%
99% 102% 16 100% 90% 100% 102% 17 100% 92% 101% 102% 18 100% 93%
102% 103% 19 100% 94% 103% 103% 20 100% 95% 104% 103% 21 100% 96%
105% 103% 22 100% 96% 105% 103% 23 100% 97% -- -- 24 -- -- --
--
TABLE-US-00057 TABLE 54 Energy, via calorimetry, relative to
control at specific time intervals for STMB cement hydrated at a
temperature between 10 and 15.degree. C. Time After Control CO2 CO2
CO2 Mixing (h) 10.degree. C. 2 min 4 min 6 min 1 -- -- -- -- 2 100%
26% 47% 61% 3 100% 54% 80% 87% 4 100% 67% 100% 103% 5 100% 75% 109%
110% 6 100% 80% 112% 111% 7 100% 83% 112% 109% 8 100% 85% 109% 106%
9 100% 88% 107% 104% 10 100% 90% 106% 103% 11 100% 92% 105% 102% 12
100% 93% 104% 101% 13 100% 94% 103% 100% 14 100% 94% 102% 99% 15
100% 94% 100% 98% 16 100% 95% 99% 98% 17 100% 95% 99% 98% 18 100%
95% 98% 97% 19 100% 96% 98% 97% 20 100% 96% 97% 97% 21 100% 96% 97%
97% 22 100% 96% 96% 97% 23 100% 96% 96% 97% 24 100% 97% 96% 97%
[0876] For the LAFB mortar, at both temperatures, the middle (4
min) dose produced the greatest enhancement of hydration, and at
both temperatures the effect started earlier than the effect for
the highest dose (6 min); in the 10 to 15 temperature, there was
already a 60% increase in hydration at the one hour time point for
the 4 min dose of carbon dioxide. For the STMB mortar, the middle
and high doses produced roughly equivalent moderate increases in
hydration at both temperatures, but the start of the effect was
markedly different for the two doses at the lower temperature,
beginning at about 9 hours for the 6 min dose and at 17 hours for
the 4 min. dose.
[0877] This Example demonstrates that carbonation of a cement mix
can have an effect on early strength development in concretes to be
batched and used at low temperatures, and that the optimal dose can
be temperature- and cement type-dependent. In addition, the timing
of onset of increased strength development can be manipulated by
manipulating the dose in some circumstances.
Example 41
[0878] This Example demonstrates the in situ formation of
nanocrystals of calcium carbonate under specific carbonation
conditions in cement.
Oil Well Cement
[0879] Laboratory scale experiments were performed on a model
system in order to better understand the impacts of the carbon
dioxide. The testing used oil well cement due to its low initial
calcite content (below detection limits on XRD). Therefore small
quantities of carbonate reaction product development could be
readily distinguished.
[0880] Samples were generated by mixing 250 g of water with 500 g
of untreated oil well cement in a blender for 30 seconds. The
blender was flooded with continuous supply of 100% CO.sub.2 gas for
a one minute during blending. Samples were flash frozen with liquid
nitrogen following the mixing period and then freeze dried to
arrest the hydration and carbonation reactions. The early hydration
was examined by sampling the batch at five distinct times
(t=immediately after the end of mixing, 5 minutes, 4 hours, 10
hours, and 24 hours after the end of mixing). A parallel set of
samples for an uncarbonated (control) system were also prepared.
Quantitative X-ray Diffraction (QXRD) was employed to characterize
the constituents of the prepared samples. Total inorganic carbon
was used to quantify the carbon dioxide.
GU Cement
[0881] An investigation was conducted to characterize the carbonate
reaction products through carbonation of a simple cement system. A
high degree of carbonation was achieved to allow for direct
observation of the crystalline reaction products.
[0882] The experiment mixed 450 g of GU cement and 50 g of
distilled deionized water in an airtight, resealable plastic bag.
The materials were hand-agitated through the bag until homogenously
blended and the cement was moistened (30 seconds). The bag was
inflated with 100% CO.sub.2 gas and sealed. The system was allowed
to react until all of the carbon dioxide had reacted (over several
minutes) and the bag had deflated. This process was repeated a
total of ten times over the course of 1 hour. A separate bag was
prepared identically, but no carbon dioxide gas was added into the
plastic bag. Carbonate content was quantified by QXRD and the
microstructure was imaged using SEM.
Oil Well Cement QXRD Results
[0883] The QXRD results of the oil well cement samples are
summarized in Table 55 (hydrated samples) and Table 56 (carbonated
series). Results are presented as percentage mass fraction per
normalized starting mass. Statistical analysis of the data
collected through QXRD suggested that the percentage error is
controlled by analytical error. An equation representing this
distribution was used to calculate all errors based on absolute
abundance. The developments of C3S, calcite, ettringite, calcium
hydroxide, and amorphous content were tracked. The Rietveld
identification of amorphous content was interpreted, in part, to
represent C--S--H gel. While the amorphous content of the anhydrous
samples would not adhere to this interpretation, the C--S--H
development would generally be associated with the net increase in
amorphous content as hydration proceeds.
TABLE-US-00058 TABLE 55 Phase Abundance Summary (wt %) via QXRD for
hydrated oil well cement series Phase Anhydrous 0 min 5 min 4 hours
10 hours 24 hours C3S 54.9 .+-. 1.2 54.5 .+-. 1.2 53.4 .+-. 1.2
49.9 .+-. 1.2 46.0 .+-. 1.2 26.4 .+-. 1.0 Calcite n/d n/d n/d n/d
0.9 .+-. 0.4 1.0 .+-. 0.4 Amorphous 8.6 .+-. 0.7 8.39 .+-. 0.7 7.6
.+-. 0.7 13.5 .+-. 0.8 20.0 .+-. 0.9 34.1 .+-. 1.1 Ettringite 0.6
.+-. 0.3 0.7 .+-. 0.4 1.1 .+-. 0.4 1.4 .+-. 0.4 1.8 .+-. 0.5 4.4
.+-. 0.6 Gyspum 4.0 .+-. 0.6 3.3 .+-. 0.6 4.5 .+-. 0.6 3.6 .+-. 0.6
3.3 .+-. 0.6 0.9 .+-. 0.4 Ca(OH).sub.2 n/d n/d n/d n/d n/d 6.0 .+-.
0.7
TABLE-US-00059 TABLE 56 Phase Abundance Summary (wt %) via QXRD for
carbonated oil well cement series Phase Anhydrous 0 min 5 min 4
hours 10 hours 24 hours C3S 54.9 .+-. 1.2 53.7 .+-. 1.2 52.3 .+-.
1.2 51.6 .+-. 1.2 42.3 .+-. 1.1 27.9 .+-. 1.0 Calcite n/d 0.8 .+-.
0.4 0.5 .+-. 0.3 1.0 .+-. 0.4 1.5 .+-. 0.4 2.8 .+-. 0.5 Amorphous
8.6 .+-. 0.7 10.4 .+-. 0.8 11.2 .+-. 0.8 13.0 .+-. 0.8 25.4 .+-.
1.0 38.3 .+-. 1.1 Ettringite 0.6 .+-. 0.3 0.6 .+-. 0.3 0.5 .+-. 0.3
0.7 .+-. 0.4 1.1 .+-. 0.4 2.5 .+-. 0.5 Gypsum 4.0 .+-. 0.6 4.1 .+-.
0.6 4.5 .+-. 0.6 4.3 .+-. 0.6 3.0 .+-. 0.6 n/d Ca(OH).sub.2 n/d n/d
n/d n/d 1.0 .+-. 0.4 5.2 .+-. 0.6
[0884] The progress of C3S dissolution and reaction is monitored by
the change in its relative abundance (decrease) with time. The
carbonated case is shown to be parallel the hydrated case wherein
the two values are equivalent within the range of error at the
initial measurement, 5 minutes and 4 hours. A greater amount C3S
has reacted in the carbonated sample (potentially 8% more) at 10
hours but by 24 hours the C3S in the two conditions is again
functionally equivalent. The carbon dioxide is shown to only have a
small effect on the overall C3S dissolution or reaction kinetics
given that that total reaction of C3S was largely the same. The
increased reaction of C3S in the carbonated oil well cement at 10
hours as observed by the QXRD agreed with the field ready-mix
concrete calorimetry (previous Examples) wherein greater energy was
released in the 7 to 11 hour interval. This stage of hydration is
associated with the end of the acceleration period when the initial
silicate hydration starts to slow down. It is possible that the
carbonate reaction products are providing a seeding role to boost
the hydration or are otherwise affecting the kinetics of the
hydration reaction.
[0885] Initial concentrations of calcite in the anhydrous cement
were below detection limits. Calcite appears in the hydrated system
after 600 min at a level of 0.90.+-.0.40%. It was unchanged through
to the end of the analysis. The large relative error (44%) is due
to the uncertainty at such low concentrations of calcite. In the
carbonated sample an increase calcite concentration is observed
immediately following the carbon dioxide gas injection
0.80.+-.0.37% by weight calcite. This level of calcite remains
relatively constant in the system through the first 4 hours. In the
sample at 10 hours the concentration of calcite increases to
1.52.+-.0.45% by weight before ultimately reaching its maximum
observed concentration of 2.83.+-.0.55% at 24 hours. The amount of
calcite in the system appears to increase but it is recognized that
no additional carbon dioxide was added to the system after the
initial mixing. The observed increase with time is likely
attributable to the calcite reaction products initially being
poorly crystalline or too small (xrd-invisible) before developing
increased crystallinity or size wherein they could be detected
through xrd.
[0886] The amorphous content of the carbonated sample is 24% higher
than that of the hydrated control immediately after carbonation. At
5 minutes it is 47% greater. It fell 4% behind at 4 hours before
accelerating to 27% ahead at 10 hours and 12% ahead at 24 hours.
The small lag at 4 hours was mirrored by the C3S content whose
consumption was shown to be slightly less for the carbonated paste
at 4 hours. The amorphous content, as it would parallel C--S--H
content and taken as a proxy for hydration progress, mirrors some
of the field observations. The field calorimetry provided evidence
of a pivot wherein hydration was slightly behind at 4 hours and
notably ahead at 10 hours before showing a strength benefit at 24
hours.
[0887] The ettringite content of the carbonated paste was found to
be lower than in the hydrated paste. If the quantification is
considered as a net increase over the trace found in the anhydrous
state then the carbonated paste contained 90% less ettringite at 4
hours, 56% at 10 hours and 49% at 24 hours. The implication is that
the ettringite was slower to form in the carbonated sample.
[0888] The gypsum content of both samples did not conclusively
change through the four hour samples. The decrease, via consumption
during hydration, was greater in the carbonated sample than the
hydrated sample. It appeared that all of the gypsum had been
consumed in the carbonated sample at 24 hours but less than 80% had
reacted in the hydrated sample.
[0889] The first detection of calcium hydroxide was in the 10 hour
sample, but only in the carbonated paste. At 24 hours the
carbonated sample had 88% of the portlandite that was detected in
the control paste.
[0890] The small dose of carbon dioxide creates nano-calcite but
does not prevent the conventional hydration reaction pathways from
proceeding. The calcium silicates continue to hydrate, while
portlandite and ettringite continue to form.
[0891] Oil Well Cement Total Inorganic Carbon Analysis
[0892] Total Inorganic Carbon (TIC) measurements were conducted for
the three states (anhydrous, hydrated and carbonated). The analysis
would account for carbon in amorphous nanoparticles of calcite that
would be insufficiently crystalline and/or too small to be observed
through QXRD.
[0893] The TIC for the anhydrous cement was 0.098%. Upon the
carbonation treatment the carbon had increased to 0.264%. At the
equivalent age the carbon content of the hydrated sample was
0.097%. and unchanged from the anhydrous sample. The TIC data
proves that carbon dioxide had entered the system even if the QXRD
was only detecting some of the ultimate value. A net increase of
0.166% was observed. This represents 0.377% CO.sub.2 by weight of
cement.
[0894] GU Cement SEM
[0895] The production of a heavily carbonated paste sample
succeeded in increasing the calcite content (normalized over the
anhydrous state) from 6.7% in the anhydrous to 37.7% in the
carbonated. Converting the calcite in % CaCO.sub.3 to % CO.sub.2,
shows that the carbonated sample had a net CO.sub.2 content of
13.6% by weight of the anhydrous cement. This level of carbonation
ensures that the reaction products are found in considerably
greater abundance than what is achieved in the industrial case.
Nonetheless, it serves as an effective system for analysis given
that the reaction products are easy to observe in a neat paste
system that has a high degree of reaction.
[0896] The electron microscopy of the carbonated sample (shown in
the micrograph of FIG. 137) revealed that numerous rhombohedral
nanocrystals were present in the system. The primary dimension of
the particles generally exceeded 10 nm and was predominantly less
than 150 nm. The sizes of the particles were too small to allow for
an effective direct chemical assessment through EDS. However, the
particle geometry is consistent with calcite and the QXRD
identified the presence of large amounts of calcite so the
conclusion is made that the carbonation process has achieved in
situ formation of nano-crystalline calcite. The production method
(extensive and aggressive carbonation) resulted in reaction
products that are likely in larger sizes and in greater quantities
than what would have been found in the industrial samples.
[0897] This Example revealed that the hydration pathways were
broadly the same with and without carbonation. The conventional
hydration phases formed after the carbonation reaction occurred.
The impact of the carbonation may have been to increase the
formation of C--S--H in the 10 to 24 hour timeframe.
Nanocrystalline, homogeneously distributed calcium carbonate was
formed in situ in the process.
Example 42
[0898] This Example outlines a liquid CO.sub.2 injection system,
for example, to accommodate dry batch ready mix plants for
efficient delivery of CO.sub.2 into the concrete trucks and
seamless installation of components. The system applies to
operations that utilize a loading boot to deposit materials into
the drum of a ready-mix truck; a loading boot is generally a
flexible, enclosed shoot that can be positioned into the hopper of
the ready-mix truck and guides materials into the drum of the
truck.
[0899] The system uses components in addition to the standard boot
components.
[0900] Additional Component Descriptions:
[0901] Rigid pipe, e.g., steel pipe (for example, ID=21/4'')
[0902] Flexible hose, e.g., flexible rubber hose (for example,
ID=P/2'')
[0903] Vacuum jacketed hose (for example, ID=3/4'')
[0904] 5-port, 4-way air solenoid valve
[0905] Telescopic air cylinder rod
[0906] Plastic slider
[0907] 3/4'' 90.degree. FNPT swivel elbow
[0908] 1/4'' Rubber air hose (.times.2)
[0909] The liquid CO.sub.2 injection system includes a flexible
hose, e.g., a rubber hose, housed in a steel pipe. The flexible
hose may be made of any suitable material that possesses sufficient
flexibility for the operations of the system, as well as the
ability to withstand the temperatures of the solid and gaseous
carbon dioxide that pass through it. The steel pipe is aligned so
that it does not extend further than the bottom of the aggregate
bin (see FIG. 135), however, the hose extends through the loading
boot and into the concrete truck's chute through the action of a
telescopic air cylinder rod (or rotary device), or other device
suitable for extending the hose, during injection. Once extended
into the chute of the concrete truck, the hose aligns itself with
the central axis of the truck to maximize concrete CO.sub.2 uptake,
but not so far as to be in contact with the destructive fins of the
truck.
[0910] The steel pipe is installed directly above the loading boot
and is mounted to, or near, the cement hopper. See FIG. 135 for an
idea of where the steel pipe should be mounted.
[0911] The pipe is positioned so that it is free of falling
materials entering the truck through the loading boot. Inside the
steel pipe is a telescopic air cylinder and rod that determines the
position of the flexible hose. The rod is controlled by an air
solenoid valve that permits the flow of air to the air cylinder at
two separate ports, one to retract the rod and the other to extend
it. The rod is connected to a plastic slider that sits inside the
steel pipe. A 90.degree. female NPT swivel elbow is installed in
the plastic slider that will be used to connect the flow of
CO.sub.2 from the CO.sub.2 supply system to the flexible rubber
hose. A long slot is cut on the side of the steel pipe to allow the
CO.sub.2 line to follow the rubber hose into its extended position.
A vacuum jacketed hose is used from the elbow to ensure the
CO.sub.2 line connected to the plastic slider remains flexible even
after injection. Due to the extreme cold of liquid CO.sub.2 a
regular hydraulic line would freeze during injection and would
become completely rigid. The vacuum jacketed hose is slightly
longer than the distance the rubber hose must travel from its
retracted to extended position, after this a copper line or
insulated hydraulic hose is permitted to the CO.sub.2 supply
system.
[0912] The injection system can be controlled manually or by any
suitable control system, such as a direct logic system, as
described below.
Direct Logic
[0913] The air solenoid valve has one input port and two output
ports. Each output port controls one end of the telescopic air
cylinder and are wired to a single pole, double throw (SPDT) relay
switch. When the relay switch does not have power it permits the
flow of air through the first solenoid valve output and keeps the
air cylinder rod retracted. The use sends a continuous 120 VAC
signal from their system to the injection system to commence the
injection sequence. Once the signal is received by the injection
system the relay switch receives power, closes one output port and
opens the other. This causes air to flow through the second output
on the air solenoid valve and allows the rod to extend. A delay is
used in the mix recipe to ensure CO.sub.2 does not start injecting
until the rod is completely extended and the flexible rubber hose
is in its correct position inside the truck. At this point the
injection system begins permitting the flow of CO.sub.2 through the
system and into the concrete truck. See FIG. 136 for a schematic of
the air cylinder rod inside the steel pipe in its retracted and
extended position. It should be noted that rotary solenoids, or
other suitable device, could also be used to extend the flexible
rubber hose into the truck, e.g., if space is an issue. This design
can be custom fitted to meet the requirements from most if not all
ready mix producers. Cleanliness permitting, the air solenoid valve
can also be mounted outside of the steel pipe and run alongside it
to reduce the length.
[0914] The user's system counts pulse signals that are sent from
the injection system that equate to a predetermined mass of
CO.sub.2. Once the required dosage of CO.sub.2 is achieved, the
user ceases the continuous 120 VAC signal and the relay switch
loses power. This causes the air cylinder rod to retract and remove
the flexible hose from the concrete truck. The injection sequence
is not complete until the rod is sufficiently retracted to be out
of the way of the trucks and falling materials. This is achieved by
a visible message on the Human Machine Interface (HMI) screen when
the retracted rod triggers a proximity sensor (or time
dependent).
Injection Sequence
[0915] The air solenoid valve is triggered once all materials have
passed though the loading boot and into the concrete truck. It is
typically the last step in the batching sequence. The injection
sequence is generally not complete until the rod has been
sufficiently retracted and out of the way of other materials
entering the loading boot. At this time a message will be displayed
to the plant's batcher that loading is complete and the driver can
leave from under the loading boot.
[0916] Typical injection sequence: [0917] 1. A concrete truck
drives under the loading boot and receives all of its materials
(aggregate, cement, water, etc.) [0918] 2. The user sends a
continuous 120 VAC signal to the injection system once all
materials have been loaded to commence the injection of CO.sub.2
[0919] 3. The injection system uses a single pole, double throw
(SPDT) relay switch to control an air solenoid valve [0920] a. When
the relay switch is normally closed, one port of the air cylinder
rod is powered to remain in its retracted position [0921] b. Once
the signal is received from the user (continuous 120 VAC signal
which stays on for the entire injection duration) the relay switch
opens and sends power to the other port on the air cylinder rod to
fully extend the rod [0922] 4. The air cylinder rod moves the
plastic slider inside the steel pipe, which pushes the rubber hose
through the boot and into the truck's chute [0923] 5. After a
pre-determined delay (generally, the time it takes for the rod to
fully extend) the injection system begins injecting CO.sub.2 into
the truck [0924] 6. The user receives pulses that equate to a mass
of injected CO.sub.2. Once the truck has received its required
dosage, the continuous 120 VAC user signal is removed and the relay
switch goes back to normally closed [0925] 7. The air cylinder rod
retracts, pulling the rubber hose back into the steel pipe away
from any falling materials in the boot [0926] 8. Once the rod is
sufficiently retracted, an "Injection Complete" message displays on
the HMI screen signaling to the driver that he is clear to pull his
truck out from under the boot
Example 43
[0927] This Example provides information on pore water composition
in cement slurries treated with various amount of carbon dioxide to
carbonate the slurry.
[0928] A slurry was made by combining 500 g of cement and 500 g of
water in a blender and mixing for 30 s. Combining cement and water
was considered the start of the experiment. In the case of the
control and lowest CO.sub.2 dosages samples were removed 2 minutes
after the experiment started. Where required CO.sub.2 was
introduced to the blender headspace over 2 minutes while mixing.
This occurred 5 minutes after the experiment started. In all cases
samples were removed from the blender at 8 and 30 minutes after the
start of the experiment, representing the period after carbonation.
Samples were filtered through a 0.22 .mu.m filter cartridge to
remove particulate producing a clear filtrate. The filtrate was
acidified using nitric acid and submitted for chemical
analysis.
[0929] The results are shown in FIGS. 138 and 139. The silicon
concentration of the pore water at an early time point (8 min)
increased with increasing dose of carbon dioxide; even a dose of
carbon dioxide as low as 0.05% bwc produced a noticeable increase
in pore water silicon concentration at this time; however, by 30
min, the silicon concentration in the pore water was virtually the
same no matter what the dose of carbon dioxide used. Power curves
generally shifted to the left with increasing dose of carbon
dioxide.
Example 44
[0930] In this Example, the effects of various degrees of
carbonation on early and late set time were examined in two
different types of cement.
[0931] The mix design was: 2700 g sand, 1070 g cement, and 535 g
water. The mixing procedure was as follows: Add sand &
water--mix 30 s; add half of cement--mix 30 s; add other half of
cement--mix 30 s; mix for additional 2 minutes applying CO.sub.2,
if required. CO.sub.2 was applied at a flow rate of 20 SLPM for
periods of 15-120 s to achieve desired level of carbonation.
Testing Procedure: Transfer all mix to set time cylinder and allow
to sit for .about.2 hrs; perform standard set time test in
accordance with ASTM C40.
[0932] The results are shown in FIGS. 140 and 141. Both initial
(FIG. 140) and final (FIG. 141) set were accelerated by
carbonation, and, generally, the greater the degree of carbonation,
the greater the acceleration of set. This was true for both
Illinois Product cement and St. Mary's Bowmanville cement, though
the magnitude of the effect was different for each.
[0933] This Example illustrates that carbonation of a cement mix
during mixing can accelerate set in a manner that is generally
dependent on the degree of carbonation, and also that the magnitude
of the effect on set time varies depending on the type of cement
used.
Example 45
[0934] In this Example the effects of addition of SCM to carbonated
mixes was investigated.
[0935] In a first test, the binder in the mix design was cement
only: 1350 g sand; 535 g cement; 241 g water; 3 mL ADVA 140
admixture. In a second test, the binder in the mix design was
cement and fly ash: 8100 g sand; 2407 g cement; 802.5 g class C fly
ash; 1445 g water; 8.4 mL Zyla 620 admixture. In each case, two
different cements were used. The mixes were carbonated at three
different doses of carbon dioxide and the 24-hour compressive
strength was compared to non-carbonated mix.
[0936] In the mixes with cement only as binder, all doses of carbon
dioxide resulted in a lower 24-hour compressible strength compared
to control for both types of cement (FIG. 142). In contrast, in the
mixes with cement and class C fly ash as binder, all doses of
carbon dioxide resulted in higher 24-hour compressive strength
compared to control for both types of cement (FIG. 143).
[0937] This Example demonstrates that the effect of carbon dioxide
is highly mix-dependent, and, in particular, subtle changes in mix
chemistry (addition of fly ash) results in noticeable changes to
strength response at 24 hours. A strength improvement was realized
when the mix contained fly ash.
Example 46
[0938] In this Example, data from 12 different industrial trials
were combined and presented graphically.
[0939] Industrial tests of carbonation of concrete mixes were
conducted in 12 different industrial locations. In most cases, at
least two or three different doses of carbon dioxide were used; the
results for the best dose are shown. Thus, the conditions can be
considered "semi-optimized," as a careful determination of the
optimum dose was generally not done. The outcomes represent a
variety of injection modes (e.g., during batching or at a wash
rack, single or serial dose); for each different injection mode,
the results for the best dose are represented. FIG. 144 represents
strength results, outliers in circles, inner darker band represents
middle 50% of results, outer darker band represents 90% of all
results, average result noted. At all time points (1, 3, 7, and 28
days) the average compressive strength of the carbonated concrete
(best dose in each trial; best dose size varied with mix design,
trial conditions) was 8-12% greater than uncarbonated control. The
highest outlier was about 190% of control compressive strength (1
day) whereas the lowest outlier was about 98% of control
compressive strength (1 day and 28 days). FIG. 145 represents
slump--the average result for CO2 conditions were 0.57'' lower than
the control, median was 0.50'' lower. This difference was
acceptable and within normal variation. FIG. 146 represents
air--average results for CO2 conditions was 0.40% lower than the
control, median was 0.20% lower. This difference was acceptable and
within normal variation.
[0940] This Example demonstrates that carbonation of concrete mixes
during mixing consistently produces a mix that has greater
compressive strength, both early and late, compared to
non-carbonated mix, with acceptable slump and air characteristics,
so long as an optimum dose for the mix and conditions is
chosen.
[0941] While preferred embodiments of the present invention have
been shown and described herein, it will be obvious to those
skilled in the art that such embodiments are provided by way of
example only. Numerous variations, changes, and substitutions will
now occur to those skilled in the art without departing from the
invention. It should be understood that various alternatives to the
embodiments of the invention described herein may be employed in
practicing the invention. It is intended that the following claims
define the scope of the invention and that methods and structures
within the scope of these claims and their equivalents be covered
thereby.
* * * * *