U.S. patent application number 09/789155 was filed with the patent office on 2001-08-16 for manufacture of improved metakaolin by grinding and use in cement-based composites and alkali-activated systems.
Invention is credited to Gruber, Karen Ann, Mathur, Sharad, Reid, Harry J..
Application Number | 20010013302 09/789155 |
Document ID | / |
Family ID | 23784958 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010013302 |
Kind Code |
A1 |
Mathur, Sharad ; et
al. |
August 16, 2001 |
Manufacture of improved metakaolin by grinding and use in
cement-based composites and alkali-activated systems
Abstract
In one embodiment, the present invention relates to a method of
making a highly reactive pozzolan, involving the steps of forming a
slurry comprising metakaolin and a liquid; wet milling the slurry;
and separating the metakaolin from the liquid to provide the highly
reactive pozolan. In another embodiment, the present invention
relates to a method of making a cement-based composition involving
the steps of providing a highly reactive pozzolan by forming a
slurry comprising metakaolin and a liquid, wet milling the slurry,
and separating the metakaolin from the liquid; and combining the
highly reactive pozzolan with at least one cementitious
material.
Inventors: |
Mathur, Sharad; (Macon,
GA) ; Gruber, Karen Ann; (Hamilton, NJ) ;
Reid, Harry J.; (Macon, GA) |
Correspondence
Address: |
AMIN ESCHWEILER & TUROCY, LLP
24TH FLOOR, NATIONAL CITY CENTER
1900 EAST 9TH STREET
CLEVELAND
OH
44114
|
Family ID: |
23784958 |
Appl. No.: |
09/789155 |
Filed: |
February 20, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09789155 |
Feb 20, 2001 |
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09449650 |
Nov 30, 1999 |
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6221148 |
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Current U.S.
Class: |
106/484 |
Current CPC
Class: |
C04B 14/106 20130101;
Y02P 40/10 20151101; C04B 28/006 20130101; C04B 28/26 20130101;
Y02P 40/165 20151101; C04B 28/04 20130101; C04B 14/106 20130101;
C04B 20/026 20130101; C04B 20/04 20130101; C04B 28/04 20130101;
C04B 2103/0088 20130101; C04B 2103/408 20130101; C04B 28/04
20130101; C04B 14/106 20130101; C04B 2103/408 20130101; C04B 28/006
20130101; C04B 14/106 20130101 |
Class at
Publication: |
106/484 |
International
Class: |
C04B 014/04 |
Claims
What is claimed:
1. A method of making a highly reactive pozzolan, comprising:
forming a slurry comprising metakaolin and a liquid; wet milling
the slurry; and separating the metakaolin from the liquid to
provide the highly reactive pozzolan.
2. The method of making a highly reactive pozzolan according to
claim 1, wherein the liquid comprises water.
3. The method of making a highly reactive pozzolan according to
claim 1, wherein the slurry comprises from about 10% to about 90%
by weight of metakaolin and from about 10% to about 90% by weight
of liquid.
4. The method of making a highly reactive pozzolan according to
claim 1, wherein the slurry further comprises a dispersant.
5. The method of making a highly reactive pozzolan according to
claim 1, wherein wet milling is conducted for a period of time from
about 1 minute to about 60 minutes at a temperature from about
-10.degree. C. to about 150.degree. C.
6. The method of making a highly reactive pozzolan according to
claim 1, wherein the metakaolin is separated from the liquid by one
of spray drying, flash drying, rotary drying, apron drying, oven
drying, and mixing the slurry.
7. The method of making a highly reactive pozzolan according to
claim 1 further comprising pulverizing the metakaolin separated
from the liquid to provide the highly reactive pozzolan.
8. A method of making a cement-based composition comprising:
providing a highly reactive pozzolan by forming a slurry comprising
metakaolin and a liquid, wet milling the slurry, and separating the
metakaolin from the liquid; and combining the highly reactive
pozzolan with at least one cementitious material.
9. The method of making a cement-based composition according to
claim 8, wherein the highly reactive pozzolan is made by heat
treating hydrous kaolin, forming a slurry comprising the heat
treated hydrous metakaolin and water, wet milling the slurry, and
separating the metakaolin from the liquid by spray drying.
10. The method of making a cement-based composition according to
claim 8, wherein the highly reactive pozzolan further comprises a
dispersant.
11. The method of making a cement-based composition according to
claim 10, wherein the dispersant comprises at least one of an
ammonia-based dispersant, a phosphate-based dispersant, a sulfonate
dispersant, a carboxylic acid dispersant and a polymeric
dispersant.
12. The method of making a cement-based composition according to
claim 8, wherein the cement-based composition comprises from about
50% to about 99.5% of the cementitious material and from about 0.5%
to about 50% of the highly reactive pozzolan.
13. The method of making a cement-based composition according to
claim 8, wherein the highly reactive pozzolan comprises from about
0.1% to about 20% by weight of the dispersant.
14. The method of making a cement-based composition according to
claim 8, wherein the cementitious material comprises portland
cement.
15. The method of making a cement-based composition according to
claim 8, wherein the separated metakaolin is pulverized prior to
being combined with at least one cementitious material.
16. The method of making a cement-based composition according to
claim 8, wherein the metakaolin is separated from the liquid by one
of spray drying, flash drying, and oven drying.
17. A method of making a highly reactive pozzolan composition,
comprising: forming a slurry comprising from about 20% to about 80%
by weight of metakaolin and from about 20% to about 80% by weight
of a liquid; and wet milling the slurry for a period of time from
about 1 minute to about 60 minutes to provide the highly reactive
pozzolan composition.
18. A highly reactive pozzolan made according to the method of
claim 1.
19. A cement-based composition made according to the method of
claim 8.
20. A highly reactive pozzolan composition made according to the
method of claim 17.
21. A method of making an alkali-activated composition comprising:
providing a highly reactive pozzolan by forming a slurry comprising
metakaolin and a liquid, wet milling the slurry for a period of
time from about 2 minutes to about 30 minutes, and separating the
metakaolin from the liquid; and combining the highly reactive
pozzolan with at least one geopolymeric material.
22. The method of making an alkali-activated composition according
to claim 21, wherein the wet milling is conducted using a Chaser
mill, Cowles mill, a Colloid mill, a Duncan mill, a Kady mill, a
Morehouse mill, a Muller mill, a Netzsch mill, a Premier mill, a
Kotthoff mill and a sedimentary delaminator.
23. The method of making an alkali-activated composition according
to claim 21, wherein the geopolymeric material is one or more of
alumino-silicate oxide, sodium hydroxide, potassium hydroxide,
water, sodium silicate, potassium silicate, Na.sub.2O, K.sub.2O, a
zeolite, silica, and alumina.
24. The method of making an alkali-activated composition according
to claim 21, wherein the alkali-activated composition comprises
from about 40% to about 99.5% by weight of one or more geopolymeric
materials and from about 0.5% to about 60% by weight of the highly
reactive pozzolan.
25. The method of making an alkali-activated composition according
to claim 21, wherein the metakaolin separated from the liquid after
wet milling has from about 5% to about 75% reduction in pore volume
compared to the metakaolin combined with water.
26. An alkali-activated composition made according to the method of
claim 21.
Description
FIELD OF THE INVENTION
[0001] This invention relates to novel methods of making a
metakaolin material well suited for cement-based composites and
alkali-activated systems.
BACKGROUND OF THE INVENTION
[0002] The use of metakaolin in cement is known. For example, U.S.
Pat. No. 4,793,861 describes a cement-based product which is
reinforced with glass fibers having good resistance to alkaline
environments. The product contains, for each 100 parts by weight of
cement, about 10 to 40 parts by weight of metakaolin, the latter
exhibiting a reactivity to the modified Chapelle test greater than
500 mg of CaO per gram of metakaolin.
[0003] U.S. Pat. No. 4,842,649 describes a blended hydraulic cement
composition composed of portland cement, slag, pozzolans including
metakaolin, and admixtures including potassium carbonate and water
reducing compositions.
[0004] U.S. Pat. No. 4,975,396 describes a process for producing
reinforced cementitious compositions in which the following
constituents are mixed in the aqueous phase in the following order:
about 35-55 parts by weight of water mixed with about 3-12 parts of
a polymer, by weight of dry polymer; up to about 5 parts of a
water-reducing auxiliary agent and/or a liquefying agent; from
about 15-30 parts of metakaolin; from about 50-120 parts of silica
sand; and about 100 parts of cement. Continuous mixing is
maintained until a homogeneous, thixotropic paste is obtained. Then
between 2 and 15% by weight of alkaline-resistant glass fibers,
relative to the weight of the paste, is introduced into the
paste.
[0005] U.S. Pat. No. 4,994,114 describes method for selecting a
pozzolan (for example metakaolin) for incorporation into a
composite material comprising cement and glass.
[0006] U.S. Pat. No. 5,167,710 describes a process for making a
cement mixture containing fibers wherein a paste is formed by
mixing cement and, per 100 parts by weight of cement, approximately
5 to 20 parts by weight of a first pulverized material of which the
grains have an average diameter of between 1/5 and {fraction
(1/10)} of the average diameter of the grains of the cement and
approximately 20 to 35 parts by weight of water. The paste is then
mixed with reinforcing fibers. The paste may also include a second
pulverized material the average grain diameter of which is between
1/5 and {fraction (1/10)} of the average diameter of the first
pulverized material.
[0007] U.S. Pat. No. 5,372,640 describes cement-based products
reinforced with alkali-resistant glass fibers that become almost
insensitive to aging when 30 to 40 parts by weight of a metakaolin
composition are added for each 100 parts of cement.
[0008] U.S. Pat. No. 5,624,489 describes a conversion-preventing
additive for high-alumina cement-based compositions, the additive
comprising: siliceous pozzolanic powder, e.g. zeolite, granulated
blast-furnace slag, fly ash, silica fume, rice hulls, metakaolin;
inorganic salts containing sodium or potassium cations and
sulphate, carbonate, nitrate, silicate, phosphate, chloride or
bromide anions, and optionally other chemical admixtures, e.g.
superplasticizers.
[0009] U.S. Pat. No. 5,626,665 describes cementitious systems
comprised of gypsum, calcined clay, and clinker.
[0010] Pozzolans are finely divided materials which can react with
alkali to form cementitious products. The fine particle size and
large pore volume of pozzolans, however, can lead to an increase in
water demand. In cement-based systems, the addition of extra water
can reduce the performance of the system by reducing the strength
and increasing the permeability of the resultant cement-based
structures. The diminished strength is undesirable for several
reasons. Initially, delay in early strength development results in
surface cracking due to evaporation. Secondly, jobs take longer
because the concrete form must remain in place substantially
longer, and finishing is delayed.
[0011] Reactive pozzolans can be made by dry grinding metakaolin
using ball milling. However, ball milling is an expensive and time
consuming process. In this connection, ball milling often requires
6 hours of milling time. Such long processing times restricts the
commercial manufacturability of dry milled pozzolans. Dry milling
is not therefore frequently employed on the raw metakaolin.
However, the addition of metakaolin to finishing mills or mills for
clinker or slag grinding (dry milling) is employed for
incorporating pozzolans into cement-based systems.
[0012] Nevertheless, there is still a need for pozzolans having
improved activity to provide cement-based systems and alkali
activated systems having lower water demand and higher compressive
strength, as well as improved flowability as a dry powder and a
higher bulk density to reduce shipping and storage costs.
SUMMARY OF THE INVENTION
[0013] This invention relates to cement-based compositions
containing a highly reactive pozzolan based upon a wet milled
metakaolin. The cement-based compositions have lower water demand
and equivalent or improved flowability in dry form compared to
conventional cement-based compositions. Resultant structures or
composites made from the cement-based compositions according to the
present invention have high compressive strength compared to
structures made from cement-based compositions made with
conventional pozzolans (dry milled metakaolin and unprocessed
metakaolin).
[0014] In one embodiment, the present invention relates to a method
of making a highly reactive pozzolan, involving the steps of
forming a slurry comprising metakaolin and a liquid; wet milling
the slurry; and separating the metakaolin from the liquid to
provide the highly reactive pozzolan.
[0015] In another embodiment, the present invention relates to a
method of making a cement-based composition involving the steps of
providing a highly reactive pozzolan by forming a slurry comprising
metakaolin and a liquid, wet milling the slurry, and separating the
metakaolin from the liquid; and combining the highly reactive
pozzolan with at least one cementitious material.
[0016] In yet another embodiment, the present invention relates to
a method of making an alkali-activated composition involving the
steps of providing a highly reactive pozzolan by forming a slurry
comprising metakaolin and a liquid, wet milling the slurry for a
period of time from about 2 minutes to about 30 minutes, and
separating the metakaolin from the liquid; and combining the highly
reactive pozzolan with at least one geopolymeric material.
[0017] In still yet another embodiment, the present invention
relates to a method of making a highly reactive pozzolan
composition involving the steps of forming a slurry comprising from
about 20% to about 80% by weight of metakaolin and from about 20%
to about 80% by weight of a liquid and wet milling the slurry for a
period of time from about 1 minute to about 60 minutes to provide
the highly reactive pozzolan composition.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The cement-based compositions of this invention are intended
for use in cement-based applications such as swimming pool
plasters, grouts, mortars and concrete. The alkali-activated
compositions of this invention are intended for use in geopolymer
and zeolitic applications such as the formation of cast and molded
bodies, the storage of toxic chemicals and radioactive waste, and
in specialty concretes. The cement-based composites or compositions
of the present invention contain at least one cementitious
material, at least one highly reactive pozzolan, and optionally at
least one dispersant. The cement-based composition is the total
combined dry mixture of the cementitious composition and highly
reactive pozzolan materials which react with water to form the
binder in concrete or other material. Concrete is a construction
material comprised of the cement-based composition, water, optional
admixtures, and aggregates.
[0019] Cementitious materials include those materials typically
required to make cement; that is, those materials that can react
with lime or other alkali and exhibit cementing properties.
Generally speaking, cementitious materials are binder materials
that harden to form a connecting medium between solids.
Cementitious materials include cements, which are any mixture of
finely-ground lime, alumina, and silica that will set to a hard
product that combines with other ingredients to form a hydrate such
as portland cement, hydraulic cements, blended cement, and masonry
cement, mortar, and related aggregate, admixtures and/or additives
including hydrated lime, limestone, chalk, calcareous shell, talc,
slag or clay.
[0020] Ordinary portland cement is a hydraulic cement produced by
pulverizing portland cement clinker. Portland cements are
classified under ASTM standards .COPYRGT.150-95 into eight types,
including: Type I for use in general concrete construction where
the special properties specified for Types II, Ill, IV and V are
not required; Type II for use in general concrete construction
exposed to moderate sulphate action, or where moderate heat of
hydration is required; Type III for use when high early strength is
required; Type IV for use when low heat of hydration is required;
Type V for use when high sulphate resistance is required; and Types
IA, IIA and IIIA, which are the same as Types I, II and III,
respectively, except that they have an air entraining agent added.
"Ordinary portland cement" in the context of this invention
includes all types (I-V and IA-IIIA) of portland cement as
referenced in ASTM C 150-95, including any cement blends
thereof.
[0021] In one embodiment, the cement-based compositions of the
present invention contain from about 50% to about 99.5% by weight
of a cementitious material. In another embodiment, the cement-based
compositions of the present invention contain from about 75% to
about 99% by weight of a cementitious material.
[0022] The alkali-activated systems of the present invention
contain at least one geopolymeric material, at least one highly
reactive pozzolan, and optionally at least one dispersant. Many
geopolymeric materials are described in U.S. Pat. Nos. 4,509,985;
5,342,595; and 5,352,427, which are incorporated by reference for
their teachings in this regard. Geopolymeric materials include one
or more of alumino-silicate oxide, strong alkalis such as sodium
hydroxide and potassium hydroxide, water, sodium and potassium
silicates, M.sub.2O compounds such as one or more of Na.sub.2O,
K.sub.2O, zeolites, silica, alumina and other metal oxides.
Generaly, alkali-activated compositions are formed by reacting
specific ratios of silica and alumina with various alkali
compounds. In the present invention, the amount of alkali that is
placed in an aqueous slurry containing metakaolin while remaining
fluid is primarily dependent upon the absorption/adsorption
characteristics of the metakaolin.
[0023] In one embodiment, the alkali-activated systems of the
present invention contain from about 40% to about 99.5% by weight
of one or more geopolymeric materials. In another embodiment, the
alkali-activated systems of the present invention contain from
about 70% to about 99% by weight of one or more geopolymeric
materials.
[0024] The cement-based compositions and the alkali-activated
systems contain at least one highly reactive pozzolan. The
cement-based compositions and the alkali-activated systems
according to the present invention have at least one of lower water
demand, higher compressive strength, and higher flowability in the
fluid state compared with cement-based compositions and
alkali-activated systems that do not contain a highly reactive
pozzolan according to the present invention.
[0025] In one embodiment, the cement-based compositions of the
present invention contain from about 0.5% to about 50% by weight of
a highly reactive pozzolan. In another embodiment, the cement-based
compositions of the present invention contain from about 1% to
about 25% by weight of a highly reactive pozzolan. In yet another
embodiment, the cement-based compositions of the present invention
contain from about 2% to about 20% by weight of a highly reactive
pozzolan.
[0026] In one embodiment, the alkali-activated systems of the
present invention contain from about 0.5% to about 50% by weight of
a highly reactive pozzolan. In another embodiment, the
alkali-activated systems of the present invention contain from
about 1% to about 25% by weight of a highly reactive pozzolan. In
yet another embodiment, the alkali-activated systems of the present
invention contain from about 2% to about 20% by weight of a highly
reactive pozzolan.
[0027] The highly reactive pozzolan is highly reactive in that the
highly reactive pozzolan has an increased dissolution of silicon
and aluminum and a decreased absorption of water and potassium
silicate in comparison to conventional metakaolin.
[0028] The highly reactive pozzolan is highly reactive further in
that composites having at least one of high compressive strengths
and low water demand are obtainable as a result of the present
invention. That is, the components of the cement-based compositions
and the alkali-activated systems of the present invention
containing the highly reactive pozzolan react and set in such a
manner that composites having high compressive strengths are
obtained compared with cement-based compositions and the
alkali-activated systems that do not contain the highly reactive
pozzolan as described herein. Although the highly reactive pozzolan
possesses little or no cementitious value, in the presence of
moisture it chemically reacts with a hydroxide, such as calcium
hydroxide, at ordinary temperatures to form compounds possessing
cementitious properties.
[0029] The highly reactive pozzolan is in the form of particles
and/or agglomerated beads of microparticles of metakaolin treated
in the manner described below. The highly reactive pozzolan may be
pulverized or non-pulverized. In one embodiment, the particles
and/or agglomerated beads have a median particle size from about 10
microns to about 100 microns (above about 10 microns). In another
embodiment, the particles and/or agglomerated beads have a median
particle size from about 15 microns to about 75 microns (above
about 15 microns). In yet another embodiment, the particles and/or
agglomerated beads have an average particle size from about 20
microns to about 50 microns (above about 20 microns).
[0030] In a preferred embodiment, the particle size distribution of
the particles and/or agglomerated beads is about 95% by weight of
the microparticles are from about 10 microns to about 75 microns.
In another preferred embodiment, the particle size distribution of
the particles and/or agglomerated beads is about 95% by weight of
the agglomerated beads are from about 15 microns to about 50
microns.
[0031] There are a number of methods and devices for measuring
particle sizes in this range. For the purposes of this invention
particle size is determined by conventional sedimentation
techniques using Micromeretics, Inc.'s SEDIGRAPH(.RTM. 5100
particle size analyzer. Particles are slurried in water with a
dispersant and pumped through the detector with agitation to
disperse loose agglomerates.
[0032] In one embodiment, the highly reactive pozzolans suitable
for use in the present invention may be prepared by a process which
comprises forming a liquid slurry comprising at least one
metakaolin, and wet grinding the metakaolin liquid slurry. Such a
slurry may be stored, and subsequently used to form a cement-based
composition or an alkali-activated composition just prior to its
intended use. In another embodiment, the highly reactive pozzolans
suitable for use in the present invention may be prepared by a
process which comprises forming a liquid slurry comprising at least
one metakaolin, wet grinding the metakaolin liquid slurry, drying
the wet milled metakaolin liquid slurry, and optionally pulverizing
the dried wet milled metakaolin. In a preferred embodiment, the
metakaolin combined with a liquid to form a slurry has a particle
size from about 0.1 micron to about 5 microns. The desired particle
size distributions of the metakaolin can be obtained by grinding or
pulverizing larger particles of metakaolin and/or through
screening, centrifuging, air classification, or other separating
means for removing undesirably sized particles, such as those
larger than about 10 microns.
[0033] Metakaolin is known to those of ordinary skill in the art
and can be prepared by calcining hydrous kaolin, which is generally
represented by the formula
Al.sub.2O.sub.3.circle-solid.2SiO.sub.2.circle-solid.2H.su- b.2O,
where the water is present as interstitial water. The metakaolin of
this invention is typically made by calcination at temperatures
from about 350.degree. C. to about 1000.degree. C., more typically
from about 500.degree. C. to about 900.degree. C. The terms
"metakaolin" and "metakaolinite" are used herein to mean an
activated product of kaolinite, produced thermally or by any other
means. The abbreviated formula for metakaolin can be written by
using the standard symbols A and S (A.dbd.Al.sub.2O.sub.3and
S.dbd.SiO.sub.2) as AS.sub.2. In a preferred embodiment, the
hydrous kaolin is not milled before it is heat treated to form
metakaolin.
[0034] A suitable amount of metakaolin is combined with a liquid to
form a slurry. The liquid is typically water but may also include
organic liquids and especially water-organic liquid mixtures.
Optionally, an effective amount of at least one dispersant is
included in the slurry to facilitate the dispersion of the
metakaolin in the liquid. These dispersants may be preformed and
added to the slurry or formed within the slurry. In one embodiment,
the cement-based compositions and/or the alkali-activated systems
also contain at least one dispersant.
[0035] The slurry is typically neutral, e.g., having a pH from
about 6 to about 8, and preferably from about 6.5 to about 7.5. The
pH of the slurry may be adjusted, if necessary, by the addition of
an acid or base so that the final pH of the slurry is approximately
neutral. Formation of the slurry is typically conducted at ambient
temperature and at atmospheric pressure. Higher or lower
temperatures and pressures may be used but are not necessary.
[0036] In one embodiment, the slurry contains from about 10% to
about 90% by weight of metakaolin and from about 10% to about 90%
by weight of liquid. In another embodiment, the slurry contains
from about 20% to about 80% by weight of metakaolin and from about
20% to about 80% by weight of liquid. In yet another embodiment,
the slurry contains from about 30% to about 70% by weight of
metakaolin and from about 30% to about 70% by weight of liquid.
[0037] Dispersants suitable for use in the present invention
include organic dispersants and inorganic dispersants. Dispersants
generally include ammonia-based dispersants and phosphate-based
dispersants. Dispersants further include sulfonate dispersants,
carboxylic acid dispersants and polymeric dispersants, such as
polyacrylate dispersants.
[0038] In one embodiment, from about 0.1% to about 20% by weight of
the metakaolin of one or more dispersants is added to the slurry.
In another embodiment, from about 0.5% to about 10% by weight of
the metakaolin of one or more dispersants is added to the slurry.
In yet another embodiment, from about 1% to about 8% by weight of
the metakaolin of one or more dispersants is added to the
slurry.
[0039] Inorganic phosphate-based dispersants include diammonium
phosphate, dipotassium phosphate, disodium phosphate, monoammonium
phosphate, monopotassium phosphate, monosodium phosphate, potassium
tripolyphosphate, sodium acid pyrophosphate, sodium
hexametaphosphate, sodium tripolyphosphate, tetrapotassium
pyrophosphate, tetrasodium pyrophosphate, tripotassium phosphate,
trisodium phosphate, urea phosphate and mixtures thereof.
[0040] Sulfonate dispersants include naphthalene sulfonates,
alkylnaphthalene sulfonates, ethoxylated alkylphenol sulfonates,
petroleum sulfonates, fatty acid sulfonates, lignosulfonates,
olefin sulfonates, amine sulfonates, and alkylaryl sulfonates.
Specific examples include those under the trade designation
Morwet.RTM. available from Witco Corp., those under the trade
designation Sellogen available from Henkel Corp., and those under
the trade designation Emkapon available from Emkay Chemical Co.
[0041] Carboxylic acids typically include organic acids and their
corresponding salts containing from about 6 to about 25 carbon
atoms. In another embodiment, carboxylic acids include organic
acids and their corresponding salts that contain from about 8 to
about 20 carbon atoms.
[0042] Polyacrylates include polyacrylic acid, salts of acrylic
copolymers, acrylic acid copolymers (for example with maleic acid),
and ammonium or alkali metal polyacrylates and polycarboxylate
salts. Specific examples include those under the trade designations
Acumer.RTM. and Acusol available from Rohm & Haas Co., those
under the trade designation Colloid available from Rhone-Poulenc
Corp., and those under the trade designation Mayosperse available
from Mayo Chemical.
[0043] In one embodiment, the cement-based compositions, the
alkali-activated systems and/or the highly reactive pozzolan also
contain at least one of water reducers and superplasticizers. A
minor amount of a flocculating agent may also be incorporated into
the mixture to facilitate dispersion/suspension of the particles in
the liquid medium. In addition, materials other than metakaolin may
be incorporated into the mixture. For example, a minor amount of
special water-soluble or water-dispersible sorbents (e.g., silicas,
aluminas or other clays) to selectively adsorb sulfur, soaps,
phosphorous or other deleterious compounds may be incorporated into
the mixture and end up in the agglomerated beads. Additional
additive materials include gypsum, alkali salts, hydrated kiln
dust, hydrated lime, fly ash, plasticizing agents, etc.
[0044] In one embodiment, the cement-based compositions, the
alkali-activated systems and/or the highly reactive pozzolans
contain a binder such as carboxymethyl cellulose, polyvinyl alcohol
and/or polyvinylpyrrolidone. In another embodiment, the
cement-based compositions, the alkali-activated systems and/or the
highly reactive pozzolans do not contain a binder such as
carboxymethyl cellulose, polyvinyl alcohol and/or
polyvinylpyrrolidone. In a preferred embodiment, the highly
reactive pozzolan composition does not contain a binder such as
carboxymethyl cellulose, polyvinyl alcohol and/or
polyvinylpyrrolidone.
[0045] In another embodiment, the cement-based compositions, the
alkali-activated systems and/or the highly reactive pozzolans
contain a minor amount of at least one binder material, preferably
a water dispersible binder. As used herein, a "water dispersible
binder" shall mean that under typical process conditions, the
binder is soluble in water or other liquid medium or is
sufficiently dispersed or suspended therein. Binders suitable for
use within the context of the present invention include alginates,
dextrin, glucose, gums, starch, waxes, glues; polymeric compounds
such as poly(vinylacetate); mineral acids such as sulfuric acid and
phosphoric acid; phosphates such as ammonium phosphate; silica
compounds such as alkaline silicates and silica hydrosol; and
colloidal clays such as attapulgite. These binder materials are
typically present in an amount up to about 10% by weight of the
highly reactive pozzolan on a moisture-free basis, preferably from
about 1% to about 5% by weight. Typically, the polymer compound, if
present as the only binder, is present in an amount up to about 3%
by weight of the highly reactive pozzolan on a moisture-free basis;
and the colloidal clay, if present as the only binder, is present
in an amount up to about 5% by weight of the highly reactive
pozzolan on a moisture-free basis (as used herein in this context
means the weight achieved after heating to a constant weight at
about 250.degree. F.).
[0046] The metakaolin slurry is then wet milled. Wet milling
procedures are known. Typically wet milling employs a drum mill,
vertical media mills, a sedimentary delaminator, or
colloid/dispersion mill. Wet milling may involve one or more of
high intensty milling, moderate intensity mill and low intensity
milling. Specific examples of wet mills include a Chaser mill,
Cowles mill, a Colloid mill, a Duncan mill, a Kady mill, a
Morehouse mill, a Muller mill, a Netzsch mill, a Premier mill, a
Kofthoff mill and various sedimentary delaminators.
[0047] In one embodiment, the metakaolin slurry is wet milled for a
period of time from about 1 minute to about 60 minutes (less than
about 1 hour). In another embodiment, the metakaolin slurry is wet
milled for a period of time from about 2 minutes to about 30
minutes (less than about 30 minutes). In yet another embodiment,
the metakaolin slurry is wet milled for a period of time from about
2.5 minutes to about 15 minutes (less than about 15 minutes). In
still yet another embodiment, the metakaolin slurry is wet milled
for a period of time from about 3 minutes to about 10 minutes (less
than about 10 minutes).
[0048] In one embodiment, the metakaolin slurry is wet milled at a
temperature from about -10.degree. C. to about 150.degree. C. In
this embodiment, an aqueous slurry contains an additive that either
lowers the freezing point or raises the boiling point of water. In
another embodiment, the metakaolin slurry is wet milled at a
temperature from about 10.degree. C. to about 80.degree. C. In yet
another embodiment, the metakaolin slurry is wet milled at a
temperature from about 15.degree. C. to about 70.degree. C.
[0049] Wet milling decreases the pore volume of the particles
and/or agglomerated beads of metakaolin. Comparing the metakaolin
used to form the slurry, and the highly reactive pozzolan made in
accordance with the present invention (metakaolin after required
processing), in one embodiment, there is from about 5% to about 75%
reduction in pore volume. In another embodiment, there is from
about 10% to about 60% reduction in pore volume. In yet another
embodiment, there is from about 20% to about 50% reduction in pore
volume.
[0050] The wet milled metakaolin slurry is dried in any suitable
manner. For example, drying may be conducted by spray drying the
slurry, flash drying the slurry, rotary drying, apron drying the
slurry, oven drying the slurry, mixing the slurry or other drying
techniques. The time required for drying varies, and primarily
depends upon the amount and identity of the liquid in the slurry.
Flash drying techniques are known in the clay industry. Spray
drying techniques are known in the clay industry. As a reference,
consult, e.g., "Atomization and Spray Drying," by W. R. Marshall
(Chemical Engineering Monograph Series, No. 2, Vol. 50 (1954)),
which is hereby incorporated by reference for its teachings in this
regard.
[0051] In spray drying, the mixture of metakaolin, liquid
(preferably water) and optional additives or ingredients is
adjusted, if necessary, by the addition of liquid so that the
metakaolin slurry is pumpable and sprayable. In one embodiment, the
concentration of metakaolin in the slurry is at least 40% by weight
of the slurry. In another embodiment, the concentration of
metakaolin in the slurry is at least 50% by weight of the slurry.
In yet another embodiment, the concentration of metakaolin in the
slurry is at least 60% by weight of the slurry. It is noted that
due to rheological considerations, smaller interactive particles
tend to make a viscous mix, so transport properties depend on the
size of the particles as well as their concentration. The mixture
or slurry is then sprayed into an atmosphere of hot, inert gases
(to this product).
[0052] Spray dryers of various designs can be used. These dryers
may be of the concurrent, countercurrent, or mixed flow type.
Nozzles, disks or the like can be used to disperse the slurry into
droplets. The temperature of the inlet and outlet air of the spray
dryer will depend, of course, on the design of the dryer. The
actual internal temperature of the agglomerated beads in the drying
chamber should be below 225.degree. F., for example from about
180.degree. F. to 200.degree. F. At these temperatures, there is
very little or no change in the crystal structure of the clay (free
water is eliminated but interstitial water is not eliminated). The
droplets thus become porous agglomerated beads of metakaolin and
are collected downstream of the drying chamber, by the usual
methods. Using a concurrent dryer, the air inlet temperature and
the clay slurry feed rate are adjusted to produce an air outlet
temperature within the range from about 250.degree. F. to about
300.degree. F.
[0053] In another embodiment, the wet milled metakaolin (mixture of
metakaolin, liquid and optional ingredients) can be agglomerated in
a mechanical mixer prior to drying. Mixing typically involves using
a high-shear mixer. A preferred type of mixer employs pins or
blades mounted radially on a rotating shaft, so that the tip of the
pin or blade, traveling at high speed, causes solid particles,
binder and water to impinge upon or contact each other in such a
way as to form an agglomerate. In time, nominally-spherical
particles tend to grow larger and larger. This phenomenon is
enhanced by the tips of the blades or pins coming very close to a
stationary wall or to a solid object (e.g., another blade or pin)
moving at a different relative rate. The vortexes set up by this
shearing motion tend to enhance the sphericity of the growing
beads.
[0054] Other less energy-intensive mechanical contacting processes
are known to those skilled in the art, including the use of drum or
dish granulators, fluidized or spouted bed granulators, or
tumbling, rotary, vibratory or gyratory granulators. For
descriptions of these processes, see, for example, Sherrington, P.
J., Granulation, Heyden & Son, Ltd., (1981), which is
incorporated herein by reference for its teaching in this regard.
These and similar devices can be used to produce granules, although
not all are optimum for making the instant invention.
[0055] Optionally after drying the wet milled metakaolin, the
metakaolin product is pulverized in any suitable manner.
Pulverization methods and apparatuses are known to those skilled in
the art. For example, pulverization may be conducted using a high
energy impact mill.
[0056] The highly reactive pozzolan contains from about 70% to
about 100% by weight of processed metakaolin (wet milled, dried,
and optionally pulverized) and from about 0% to about 30% of one or
more dispersants and additives. In another embodiment, the highly
reactive pozzolan contains from about 80% to about 99.5% by weight
of metakaolin microparticles and from about 0.5% to about 20% of
one or more dispersants and additives. In yet another embodiment,
the highly reactive pozzolan contains from about 90% to about 99%
by weight of metakaolin microparticles and from about 1% to about
10% of one or more dispersants and additives.
[0057] In one embodiment, the highly reactive pozzolan is combined
with one or more cementitious materials to form a cement-based
composition. Cement paste is made by adding water to the
cement-based composition. Swimming pool plaster, grouts, concrete
and mortar are made by combining water, the cement-based
composition, and any desired aggregate, admixtures or additives. In
another embodiment, the highly reactive pozzolan is combined with
one or more geopolymeric materials including alkali containing
products to form an alkali-activated system or composition for cast
and molded bodies, the storage of toxic chemicals and radioactive
waste, and in specialty concretes.
[0058] ASTM C 109/109M-95 quantifies the compressive strength of
hydraulic cement mortars. The number following the ASTM test method
number indicates that it is the ASTM test method in effect during
that specific year, such as 1995 in the case where 95 follows the
ASTM test method. The compressive strength is the measured maximum
resistance of a specimen to axial compressive loading normally
expressed as force per unit cross-sectional area. Although the ASTM
test methods are set out specifically, those skilled in the art may
be aware of alternative methods which could be used to test for the
referenced qualities or results. The only difference being, the
results or qualities may be reported in a different manner wherein
a conversion system could be used to give comparable results.
Consequently, the invention should not be limited by the referenced
test methods and the results thereof, but rather only to the claims
as set forth below taking into account equivalent testing methods
and results.
[0059] Examples of this invention are included hereinbelow. Of
course, the examples are not intended as limiting this invention as
modification of the examples by ordinary expedient will be readily
apparent to those of ordinary skill in the art. Unless otherwise
indicated in the following examples and elsewhere in the
specification and claims, all parts and percentages are by weight,
temperatures are in degrees Celsius, pressures are at or near
atmospheric.
[0060] Several mortar compositions, both according to the present
invention and not according to the invention are made and compared.
In the compositions, a cement-based composition of 80% by weight
mortar cement and 20% by weight of a metakaolin (the metakaolin is
varied as specified below) is combined with water with a
water-to-cement ratio of 0.4. Sand is added as aggregate in an
amount so that the sand:cementitious weight ratio is 2.75
(cementitious in these examples refers to mortar cement and
metakaolin). Comparative Example 1 is made with metakaolin
(untreated). Comparative Example 2 is made with dry milled
metakaolin (ball milled for 6 hours). Comparative Example 3 is made
with metakaolin that is slurried and spray dried. Example 1 is made
with metakaolin that is wet milled (in a Netzsch mill for 5
minutes), spray dried, and pulverized. Example 2 is made with
metakaolin that is wet milled (in a Netzsch mill for 5 minutes) and
spray dried. Example 3 is made with metakaolin that is wet milled
(in a sedimentary delaminator for 15 minutes), oven dried, and
pulverized.
[0061] The extent of dissolution of aluminum and silicon ions in
compositions made with pozzolans manufactured according to the
present invention and not according to the invention is examined.
Generally, the higher dissolution of aluminum and silicon ions, the
faster the composition reacts. Dissolution is measured by
quantifying the amount of leaching in a 30% KOH solution. The
results are reported in Table 1.
1 TABLE 1 5 minute leach 15 minute leach Example Al, ppm Si, ppm
Al, ppm Si, ppm C. Ex. 1 50 60 -- -- C. Ex. 2 418 318 462 379 C.
Ex. 3 69 69 90 90 Ex. 1 272 245 364 348 Ex. 2 180 162 258 246 Ex. 3
136 122 170 158
[0062] The extent of potassium silicate absorption in compositions
made with pozzolans made according to the present invention and not
according to the invention is examined next. Generally, the lower
the potassium silicate absorption, the lower the water demand of
the composition (and thus a higher resultant compressive strength).
Potassium silicate absorption is measured by quantifying the amount
of potassium silicate absorbed in a 30% KOH solution. The results
are reported in Table 2. Although Comparative Example 2 has a low
potassium silicate absorption, it involves dry milling metakaolin
for 6 hours while Examples 1, 2, and 3 involve wet milling
metakaolin for 5 minutes, 5 minutes, and 15 minutes, respectively,
which is an enormous time savings in the manufacturing process.
2 TABLE 2 Example potassium silicate absorption C. Ex. 1 0.9 C. Ex.
2 0.6 C. Ex. 3 0.83 Ex. 1 0.62 Ex. 2 0.63 Ex. 3 0.58
[0063] The flowability of compositions made with pozzolans made
according to the present invention and not according to the
invention is examined in accordance with ASTM 230. Generally, the
higher the flow, the lower water demand of the composites made in
accordance with the present invention. Flowability of the fresh
mortar can also be used as a measure of the workability of a given
mixture. The results are reported in Table 3.
3 TABLE 3 Example Flow C. Ex. 1 47 mm Ex. 3 56 mm
[0064] The compressive strength over time is examined. Each mortar
composition is formed into a 2 inch cube and the compressive
strength is tested. The reported compressive strengths represent
the average of testing two cubes (for each composition at each
testing age). When not under testing, the mortar cubes are stored
in lime water. The results are reported in Table 4.
4 TABLE 4 Compressive Strength (psi) Testing Age (days) Ex. 3 C.
Ex. 1 1 3,665 3,810 3 6,840 6,500 7 8,845 8,385 28 9,710 9,455
[0065] Two additional mortar compositions, one according to the
present invention and one not according to the invention are made
and compared. In the two compositions, a cement-based composition
of 80% by weight mortar cement and 20% by weight of a metakaolin
(the metakaolin is varied as specified below) is combined with
water with a water-to-cement ratio of 0.4. The same amount of water
is added to each of the two compositions. Sand is added as
aggregate in an amount so that the sand:cementitious weight ratio
is 2.75 (cementitious in these examples refers to mortar cement and
metakaolin). Comparative Example 4 is made with metakaolin
(untreated). Example 4 is made with metakaolin that is wet milled
(in a Netzsch mill for 5 minutes) and spray dried.
[0066] The flowability of the two compositions is examined in
accordance with ASTM 230. Generally, the higher the flow, the lower
water demand of the composites made in accordance with the present
invention. Flowability can also be used as a measure of the
workability of a given mixture. The results are reported in Table
5.
5 TABLE 5 Example Flow C. Ex. 4 40 mm Ex. 4 47 mm
[0067] The compressive strength over time is examined. Each mortar
composition is formed into a 2 inch cube and the compressive
strength is tested. The reported compressive strengths represent
the average of testing two cubes (for each composition at each
testing age). When not under testing, the mortar cubes are stored
in lime water. The results are reported in Table 6.
6 TABLE 6 Compressive Strength (psi) Testing Age (days) Ex. 4 C.
Ex. 4 1 3,930 3,840 3 6,785 6,675 7 8,425 8,335 28 9,630 9,630
[0068] In one embodiment, the amount of water combined with the
cement-based compositions and alkali-activated systems according to
the present invention is about 5% less than that required to obtain
the same flowability compared to conventional cement-based
compositions and conventional alkali-activated systems such as
those made with conventional pozzolans including untreated
metakaolin (other than water, the amounts of other components, such
as optional additives, are the same). In another embodiment, the
amount of water combined with the cement-based compositions and
alkali-activated systems according to the present invention is
about 10% less than that required to obtain the same flowability
compared to conventional cement-based compositions and conventional
alkali-activated systems such as those made with conventional
pozzolans including untreated metakaolin (other than water, the
amounts of other components, such as optional additives, are the
same). In yet another embodiment, the amount of water combined with
the cement-based compositions and alkali-activated systems
according to the present invention is about 20% less than that
required to obtain the same flowability compared to conventional
cement-based compositions and conventional alkali-activated systems
such as those made with conventional pozzolans including untreated
metakaolin (other than water, the amounts of other components, such
as optional additives, are the same). This is a notable improvement
since a lower water demand is typically associated with an increase
in density and an increase in strength.
[0069] The mortar compositions made in accordance with the present
invention not only exhibited superior workability, but also
superior compressive strength. It is difficult to simultaneously
improve both workability and compressive strength, yet the present
invention provides cement-based compositions and alkali-activated
systems exhibiting both improved workability and compressive
strength.
[0070] While the invention has been explained in relation to its
preferred embodiments, it is to be understood that various
modifications thereof will become apparent to those skilled in the
art upon reading the specification. Therefore, it is to be
understood that the invention disclosed herein is intended to cover
such modifications as fall within the scope of the appended
claims.
* * * * *