U.S. patent application number 13/467450 was filed with the patent office on 2013-11-14 for chemically active glasses for steel enamels.
The applicant listed for this patent is Richard K. Brow, Genda Chen, Signo T. Reis. Invention is credited to Richard K. Brow, Genda Chen, Signo T. Reis.
Application Number | 20130302607 13/467450 |
Document ID | / |
Family ID | 49548840 |
Filed Date | 2013-11-14 |
United States Patent
Application |
20130302607 |
Kind Code |
A1 |
Brow; Richard K. ; et
al. |
November 14, 2013 |
CHEMICALLY ACTIVE GLASSES FOR STEEL ENAMELS
Abstract
A corrosion resistant steel reinforcing rod system, including a
steel reinforcing rod having a coefficient of thermal expansion of
between about 14 ppm/.degree. C. and about 17 ppm/.degree. C. and a
vitreous shell substantially encapsulating the steel reinforcing
rod. The vitreous shell has a composition selected from the group
consisting essentially, in weight percent, of about 40-45%
SiO.sub.2, 3-5% Al.sub.2O.sub.3, 5-15% B.sub.2O.sub.3, 3-15%
K.sub.2O, 5-20% Na.sub.2O, 4-7% CaO, 1-2% ZrO.sub.2, 0-2% NiO, 0-2%
CoO, and 5-20% P.sub.2O.sub.5. The vitreous shell has a coefficient
of thermal expansion between about 12.5 ppm/.degree. C. and about
13.5 ppm/.degree. C.
Inventors: |
Brow; Richard K.; (Rolla,
MO) ; Reis; Signo T.; (Rolla, MO) ; Chen;
Genda; (Rolla, MO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Brow; Richard K.
Reis; Signo T.
Chen; Genda |
Rolla
Rolla
Rolla |
MO
MO
MO |
US
US
US |
|
|
Family ID: |
49548840 |
Appl. No.: |
13/467450 |
Filed: |
May 9, 2012 |
Current U.S.
Class: |
428/384 ;
106/644; 427/401; 428/390 |
Current CPC
Class: |
E04C 2/06 20130101; Y10T
428/2949 20150115; Y10T 428/296 20150115; E04C 5/015 20130101 |
Class at
Publication: |
428/384 ;
427/401; 428/390; 106/644 |
International
Class: |
E04C 5/01 20060101
E04C005/01; E04C 2/06 20060101 E04C002/06 |
Goverment Interests
GRANT STATEMENT
[0002] The invention was made in part from government support under
Grant No. W911NF-07-2-0062 from the Department of the Army. The
U.S. Government has certain rights in the invention.
Claims
1. A corrosion resistant steel reinforcing rod system, comprising:
a steel reinforcing rod; and a vitreous shell generally
encapsulating the steel reinforcing rod; wherein the vitreous shell
has a composition selected from the group consisting essentially,
in weight percent, of about 40-45% SiO.sub.2, about 5-25%
B.sub.2O.sub.3, about 5-25% Na.sub.2O, and about 5-20%
P.sub.2O.sub.5.
2. The system of claim 1 wherein the vitreous shell has a
P.sub.2O.sub.5 content of between about 9 and about 18 weight
percent.
3. The system of claim 1 wherein the vitreous shell is enveloped in
a cementitious matrix; wherein there are apertures in the vitreous
shell exposing the portions steel rod to the cementitious matrix;
wherein phosphate is released from the vitreous shell; and wherein
hydroxyapatite is deposited onto exposed portions of the steel
reinforcing rod.
4. A composite structural material comprising in combination: a
cementitious matrix; a plurality of steel reinforcing rods
positioned in the cementitious matrix; and a plurality of vitreous
shells, each respective vitreous shell generally covering a
respective steel reinforcing rod; wherein each respective steel
reinforcing rod has a coefficient of thermal expansion of between
about 14 ppm/.degree. C. and about 17 ppm/.degree. C.; and wherein
each respective vitreous shell has a composition selected from the
group consisting essentially, in weight percent, of about 40-45%
SiO.sub.2, 3-5% Al.sub.2O.sub.3, 5-25% B.sub.2O.sub.3, 3-15%
K.sub.2O, 5-25% Na.sub.2O, 4-7% CaO, 1-2% ZrO.sub.2, 0-2% NiO, 0-2%
CoO, and 5-20% P.sub.2O.sub.5; and wherein each respective vitreous
shell has a coefficient of thermal expansion between about 12.5
ppm/.degree. C. and about 13.5 ppm/.degree. C.
5. The composite structural material of claim 4 wherein there are
apertures in the vitreous shell exposing the portions of the steel
rods to the cementitious matrix; wherein phosphate is released from
the vitreous shell; and wherein hydroxyapatite is deposited onto at
least some of the exposed portions of the steel reinforcing
rods.
6. The composite structural material of claim 4 wherein the bond
strength of the steel reinforcing rods in the cementitious matrix
increases over time.
7. A method of reinforcing concrete, comprising: coating a
plurality of steel reinforcing members with phosphate-rich glass
layers for emplacement into a cementitious matrix, wherein the
respective steel reinforcing members have a first coefficient of
thermal expansion and wherein the respective glass layers have a
second coefficient of thermal expansion substantially matching the
first coefficient of thermal expansion; and forming a cementitious
matrix around the plurality of steel reinforcing members; releasing
phosphate from the glass layers; and forming a hydroxyapatite layer
on steel surfaces not coated with glass.
8. The method of claim 7 wherein the glass layers have a
composition selected from glasses consisting essentially, in weight
percent, of about 40-45% SiO.sub.2, 3-5% Al.sub.2O.sub.3, 5-15%
B.sub.2O.sub.3, 3-15% K.sub.2O, 5-20% Na.sub.2O, 4-7% CaO, 1-2%
ZrO.sub.2, 0-2% NiO, 0-2% CoO, and 5-20% P.sub.2O.sub.5.
9. The method of claim 7 wherein the glass layers have a
coefficient of thermal expansion between about 12.5 and 13.5 ppm
per degree Celsius.
10. The method of claim 7 wherein the glass layers contain about 9
to about 18 weight percent P.sub.2O.sub.5.
11. A steel reinforcing rod system, comprising: a steel reinforcing
rod having a coefficient of thermal expansion of between about 14
ppm per degree Celsius and about 17 ppm per degree Celsius; a
vitreous shell generally encapsulating the reinforcing rod; a
plurality of metal particles distributed throughout the vitreous
shell; wherein the vitreous shell has a composition selected from
the group consisting essentially of about 40-45% SiO.sub.2, 3-5%
Al.sub.2O.sub.3, 5-25% B.sub.2O.sub.3, 3-15% K.sub.2O, 5-25%
Na.sub.2O, 4-7% CaO, 1-2% ZrO.sub.2, 0-2% NiO, 0-2% CoO, and 5-20%
P.sub.2O.sub.5; and wherein the vitreous shell has a coefficient of
thermal expansion between about 12.5 ppm per degree Celsius and
about 13.5 ppm per degree Celsius.
12. The system of claim 11 further comprising a cementitious matrix
adjacent to and generally surrounding the vitreous shell; wherein
there are apertures in the vitreous shell exposing portions of the
steel rods to the cementitious matrix; wherein phosphate is
released from the vitreous shell; and wherein hydroxyapatite is
deposited onto at least some of the portions of the steel
reinforcing rods exposed to the cementitious matrix.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims priority to co-pending U.S.
patent application Ser. Nos. 13/040,781, filed Mar. 4, 2011, which
claims priority to Ser. No. 12/623,236, filed Nov. 20, 2009, and
issued on Mar. 8, 2011 as U.S. Pat. No. 7,901,769, which claims
priority to U.S. Provisional Patent Application Ser. No.
61/199,901, filed Nov. 21, 2008.
TECHNICAL FIELD
[0003] The present invention relates to structural materials and,
more particularly, to a new and improved glass composite developed
for coating steel elements for reinforcing concrete structures.
BACKGROUND
[0004] One material very commonly selected for large-scale
construction projects is reinforced concrete (RC). Several years
ago, it was discovered that the use of a modified vitreous enamel
improved the bond strength, and, possibly, the corrosion resistance
of the steel rods reinforcing the concrete. The enamel consisted of
a glass matrix embedded with reactive ceramic particles. The glass
composition was found to strongly adhere to the steel, and the
reactive particles were imbedded to chemically react with the
surrounding cement to form another strong bond.
[0005] The materials used for these initial tests included
commercial alkali-resistant groundcoat enamelss for steels used in
a variety of consumer and industrial applications. The typical
compositional ranges for such enamels are summarized below as Table
1.
TABLE-US-00001 TABLE 1 Compositional ranges for typical
alkali-resistant groundcoats Constituent Range (wt %) Silicon
dioxide SiO.sub.2 40-45 Boron oxide B.sub.2O.sub.3 16-20 Na oxide
Na.sub.2O 15-18 K oxide K.sub.2O 2-4 Li oxide Li.sub.2O 1-2 Ca
oxide CaO 3-5 Aluminum oxide Al.sub.2O.sub.3 3-5 Zr oxide ZrO.sub.2
4-6 Mn dioxide MnO.sub.2 1-2 Ni oxide NiO 1-2 Cobalt oxide
Co.sub.3O.sub.4 0.5-1.5 Phosphorus oxide P.sub.2O.sub.5
0.5-1.sup.
[0006] The ratio of the Na.sub.2O, B.sub.2O.sub.3, and SiO.sub.2
components, as well as the addition of other alkali (K.sub.2O and
Li.sub.2O) and alkaline earth oxides (CaO), have the greatest
effect on the thermal properties of the glass. Constituents like
Al.sub.2O.sub.3 are added to improve the corrosion-resistance of
the glass. ZrO.sub.2 is usually added to an enamel as an opacifier
to affect the visual appearance of the coating. However, zirconia
has the added advantage of improving the chemical resistance of
silicate glasses to attack by alkaline environments.
Alkaline-resistant silicate glass fibers developed for reinforcing
cement composites typically contain 10-20 wt % ZrO.sub.2, and a
protective coating of Zr-oxyhydroxide forms on the glass surface
when exposed to an alkaline environment, further impeding
corrosion. Transition metal oxides, like MnO.sub.2,
Co.sub.3O.sub.4, and NiO, are added to enamels to aid bonding to
the substrate.
[0007] In general, these materials are sodium-borosilicate glasses
modified with various constituents to tailor thermal and chemical
properties. However, the conventional groundcoat enamels (such as
the ones listed in Table 1) only offer limited protection to the
underlying steel if they are cracked or otherwise damaged. If the
cementitious material can directly contact the steel, such as
through chips, holes or cracks in the glass or enamel coating, the
steel is then locally attacked by the corrosive cementitious
material. Therefore, there is a need to provide a new and improved
glass or enamel composition offering enhanced corrosion resistance
to the steel, as well as corrosion resistance even if cracked or
broken. The present novel technology addresses these needs.
SUMMARY
[0008] The present novel technology relates to a chemically-active
glass composition for providing corrosion protection to coated
steels for use in alkaline environments.
[0009] One object of the present novel technology is to provide an
improved steel reinforced concrete system including the same.
Related objects and advantages of the present novel technology will
be apparent from the following description.
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIG. 1 is a cutaway perspective view of a steel rod coated
with a vitreous material according to a first embodiment of the
present novel technology.
[0011] FIG. 2A is a perspective view of a first plurality of steel
rods according to FIG. 1 embedded in a cementitious material to
yield a first composite material according to a second embodiment
of the present novel technology.
[0012] FIG. 2B is an enlarged partial view of one of the embedded
rods of FIG. 2A.
[0013] FIG. 3A is a perspective view of a second plurality of steel
rods according to FIG. 1 embedded in a cementitious material to
yield a second composite material according to a second embodiment
of the present novel technology.
[0014] FIG. 3B is an enlarged partial view of one of the embedded
rods of FIG. 2A.
[0015] FIG. 4 shows weight changes for glasses after up to 28 days
in alkaline Lawrence Solution at 80.degree. C.
[0016] FIG. 5 shows the comparisons of average bond strengths (in
MPa) for steel pins embedded in mortar after up to 60 days.
[0017] FIG. 6 is a graphical representation of the change in linear
dimension vs. temperature of a steel rod and two vitreous coating
compositions for the coated steel rods of FIG. 1.
[0018] FIG. 7 is a cutaway perspective view of a steel rod coated
with a phosphate-releasing glass according to a third embodiment of
the present novel technology.
[0019] FIG. 8A is a perspective view of a second plurality of steel
rods according to FIG. 7 embedded in a cementitious material.
[0020] FIG. 8B is a first enlarged is an enlarged partial view of
one of the embedded rods of FIG. 8A illustrating direct contact of
an exposed portion of a steel rod with cement.
[0021] FIG. 8C is a second is an enlarged partial view of one of
the embedded rods of FIG. 8A illustrating the formation of a
barrier patch at the exposure site.
DETAILED DESCRIPTION
[0022] For the purposes of promoting an understanding of the
principles of the novel technology and presenting its currently
understood best mode of operation, reference will now be made to
the embodiments illustrated in the drawings and specific language
will be used to describe the same. It will nevertheless be
understood that no limitation of the scope of the novel technology
is thereby intended, with such alterations and further
modifications in the illustrated device and such further
applications of the principles of the novel technology as
illustrated therein being contemplated as would normally occur to
one skilled in the art to which the novel technology relates.
[0023] Unless otherwise defined, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs.
[0024] In one embodiment, steel reinforcing rods 10 are coated with
the novel glass composition 20 to yield coated reinforcing rods 30.
The glass coating 20 is particularly suitable for coating the steel
alloys used in the rods 10, as the glass coating 20 typically has a
coefficient of thermal expansion close to but lower than that of
the steel rods 10, such that the glass coating 20 is maintained in
compression. Further, the glass coating 20 is substantially more
corrosion resistant than the conventional enamel coatings known in
the art. Specifically, the thermal properties of the glass coatings
are tailored for the steel alloys used in RC structures, which have
different thermal expansion coefficients than the alloys used in
commercial and industrial applications for which the conventional
groundcoat compositions were designed. Typically, the steel alloys
used in the rods 10 are ASTM A 615, 706, 955, 996 or the like,
which typically have thermal expansion coefficients of from about
14 ppm/.degree. C. to about 17 ppm/.degree. C. The glass coating 20
typically has a thermal expansion coefficient of between about 12.5
ppm/.degree. C. and about 13.5 ppm/.degree. C. at ambient
temperatures typical of most applications.
[0025] In particular, the borate-to-silicate ratio and the fraction
and type of alkali oxide of the coatings 20 has been optimized to
yield coatings 20 characterized by greater CTE to improve the
thermomechanical compatibility with typical reinforcing steel. In
other words, the CTE of the glass coatings 20 has been raised to be
closer to that of typical steel rebars 10 while remaining slightly
lower than the steel CTE, such that the glass coating 20 is put
into compression 20 but not so much so that it fails and disengages
therefrom. Further, this CTE matching was accomplished without
sacrificing chemical durability of the glass coating 20. Thus, by
better matching the thermomechanical properties of the glass
coatings 20 to the steel members 10, the glass coatings 20 are less
prone to failure due to stresses arising from thermal cycling and
thus remain on the steel members 10 where they can participate in
the bonding process with a surrounding cementitious matrix
material.
[0026] Additionally, the corrosion resistance of the glass coatings
20 is especially attractive in alkaline environments. The glass
coatings 20 typically includes substantially increased
concentrations of CaO, K.sub.2O and, more typically, ZrO.sub.2 at
levels substantially greater than the typical enamel compositional
ranges to provide increased corrosion resistance of the glass
coated rods 30 in alkaline environments.
[0027] In some embodiments, as seen in FIGS. 2A-3B, cement-reactive
particles 35, such as calcium silicate, are dispersed in the glass
coatings 20 to enhance bonding with a cement matrix 40 to result in
a steel-reinforced concrete composite material 50 having increased
bond strength between the coated rods 30 and the cement matrix 40.
Such a material 50 will exhibit a substantially increased pull-out
strength and be inherently tougher. Optionally, metal particles 45
such as zinc may be dispersed in the glass coating 20 to act as
sacrificial anodes for further protecting the steel rods 30 from
the corrosive effects of the cementitious matrix 40. Still
optionally, such sacrificial anode particles 45 may be added
directly to the cement, either throughout or preferentially near
the steel rods 10, to react locally with the corrosive cementitious
matrix 40 to divert its attack on the steel rods 10. As they are
corroded, the sacrificial metal particles 45 will expand to provide
both physical as well as chemical protection, chemically reacting
with corrosives and physically blocking the corrosion pathways.
[0028] Table 2 shows the compositions of several embodiments of the
glass coating 20, along with test results of the dilatometric
softening point and the CTE, designated ARE-1 through ARE-5. For
comparison, the composition and properties of a standard
(conventional) alkali-resistant groundcoat composition is presented
and designated ARG.
TABLE-US-00002 TABLE 2 Comparision between the novel glass coating
compositions and ARG ARE- ARE- ARE- ARE- ARE- ARE- wt % 1 2 3 4 5
11 ARG SiO.sub.2 44.5 43.4 39.7 42.0 33.2 39.3 44.0 B.sub.2O.sub.3
17.9 14.4 14.0 13.9 19.2 13.0 19.3 Na.sub.2O 15.9 15.5 15.1 8.9 8.6
8.3 15.8 K.sub.2O 4.3 4.2 4.1 13.5 13.0 12.6 2.8 CaO 5.1 5.0 4.8
4.8 4.6 4.5 4.7 CaF.sub.2 Al.sub.2O.sub.3 3.6 3.8 3.7 3.6 3.5 3.4
4.6 ZrO.sub.2 5.6 10.9 10.6 10.6 15.3 9.9 5.3 MnO.sub.2 0.7 0.6 0.6
0.6 0.6 0.6 1.5 NiO 1.1 1.1 1.1 1.1 1.0 1.0 1.0 CoO 1.1 1.1 1.1 1.1
1.0 1.0 0.9 P.sub.2O.sub.5 0 0 0 0 0 6.4 Soft Temp 600 586 600 600
594 610 576 (.degree. C.) CTE 13.5 12.9 12.5 12.9 12.7 10.8 12.2
(ppm/.degree. C.)
[0029] FIG. 4 shows the change in weight for glass samples after up
to 28 days at 80.degree. C. in Lawrence solution (pH=13). The
K.sub.2O and ZrO.sub.2 contents of the ARE-series glass coatings 20
are each, respecitvely, greater than those of the ARG composition,
and the weight changes of ARE compositions 2 and 5 are respectively
less than that of the ARG glass.
[0030] In another embodiment, reinforced concrete 50 was prepared
by the pouring wet concrete over coated rods 30 and allowing the
concrete to dry and cure to define a concrete matrix 40, yielding a
reinforced concrete composite material 50. The bonding of the
coated rods 30 in the concrete matrix 40 was analytically
measured.
[0031] A series of pull-out tests was conducted to assess the bond
strengths of the embedded coated rods 30 with several compositional
embodiments of the glass coating material 20. The results of
pull-out testing are shown in FIG. 5.
[0032] Preparation of Test Mortar.
[0033] Uncoated steel rods 10 and coated rods 30 were embedded in a
mortar prepared using the guidelines presented in ASTM C109,
Standard Method for Determining Compressive Strength of Hydraulic
Mortars. The proportion of the standard mortar was one part cement
(Type I) to 2.75 parts of standard graded sand. The water-to-cement
ratio was maintained at 0.485. Test cylinders were prepared for
each mortar batch and tested to investigate the compressive
strength at 7 and 30 days.
[0034] Preparation and Testing of Embedded Rods for Pull-out
Testing.
[0035] Each uncoated 10 and glass coated test rod 30 was inserted
in a 50.8-mm in diameter, 101.6-mm long plastic cylinder mold
filled with fresh mortar. The respective rods 10, 30 were clamped
at the top so that a 63.5-mm length of each respective rod 10, 30
was under the mortar; for the coated rods 30, the portion under
mortar was glass coated. Each cylinder was tapped and vibrated to
remove entrapped air and also to consolidate the mortar. The
samples were kept in a 100% humidity environment at room
temperature and cured, with curing times ranging from 7 days and to
60 days. After curing, the test cylinders were de-molded and the
mounted in the test apparatus and the force required to pull each
respective rod 10, 30 out of the mortar was measured.
[0036] The testing pin-pull results for steel after up to 60 days
in mortar indicate that the bond strength of the uncoated pins
decreases from about 4 MPa to about 2.2 MPa between seven days and
28 days of curing. This is consistent with reports in the
literature for decreasing bond strength between cement paste and
reinforcing steel with increasing curing time age, particularly
from 1 to 14 days. However, due the hydration reaction of cement
with the reactive Ca-silicate particles used for the glass coated
samples 30, these bond strengths increase from 1.2 MPa to 6.60 kPa
with an increase of curing time from three days to 60 days.
Further, glass coated steel pins 30 with reactive calcium silicate
have about three times the bond strength of bare steel pins after
60 days in cement.
[0037] Steel-reinforced concrete composite material 50 benefitting
from increased bond strength and decreased degradation of the steel
10 from corrosive attack by the concrete matrix 40 give rise to a
number of uses, such a structural material for floors and decking,
hardened or reinforced civilian and military structures, sewage
pipe, geotechnical anchorages, and the like. Further, the strong
bond formed between the glass-coated steel 30 (with or without
calcium silicate particles or the like dispersed therein as bonding
enhancers) and the cementitious material 40 enables design options
such as concrete-filled steel tubes or casings.
[0038] Further, the glass composition may be optimized to be
self-sealing. As the glasses have relatively low softening
temperatures, they are well suited for low temperature
applications, such as retrofit and remediation applications.
Additionally, glass-tape composites may be made with these
compositions that may be wrapped around steel members and then
fused thereto via the direct application of heat, such as by
induction or a torch, to provide corrosion protection and/or an
enhanced bonding surface.
[0039] Referring to FIG. 6, the change in linear dimension as a
function of time is plotted for both a steel rod 10 and for two
coating compositions (ARE-4 and ARE-11P). The rod 10 has a measured
CTE of 16.9 ppm/degrees Celsius, while the ARE-4 composition has a
CTE of 12.9 ppm/degree Celsius and the ARE-11P has a CTE of 10.8
ppm/degree Celsius. The CTE of the rod 10 is substantially constant
over a temperature range of about 100 to about 700 degrees Celsius,
while the CTE's of the glass coating compositions are substantially
constant over ranges of between about 200 to about 450 degrees
Celsius. Both compositions appear to beging to soften at about 500
degrees Celsius, resulting in a change in CTE in the 500 to 600
degree Celsius range.
[0040] The desired properties of the novel glass composite include
1) a coefficient of thermal expansion (CTE) that is more compatible
with the steel alloy that is to be coated, 2) a softening
temperature that is relatively low (<700 degrees Celsius) to
ensure low processing temperatures that do not degrade the
mechanical properties of the steel, and 3) outstanding
corrosion-resistance to the alkaline environment of wet cement. The
novel glass composite comprises at least 4.0% (wt) K.sub.2O and at
least 5.6% (wt) ZrO.sub.2, with about 4-20% (wt) of K.sub.2O,
and/or about 5-20% (wt) of ZrO.sub.2, whereas both K.sub.2O and
ZrO.sub.2 are significantly increased compared to the conventional
groundcoats.
[0041] In another embodiment, as shown in FIGS. 7-8B,
chemically-active glass compositions 100 may be used to coat steel
rods 10 to provide enhanced corrosion-protection steel members 130
used for reinforcing cementitious matrices 40 or reinforced
concrete 50, while still providing the desired characteristics
(e.g., thermal properties like coefficient of thermal expansion and
softening temperature) for use with the composite enamels to
enhance steel-concrete bond strengths. Specifically, the glass 100
releases phosphate anions when exposed to a corrosive alkaline
environment, such as that characteristic of a cementitious matrix
40. The phosphate anions react at exposed surfaces of steel 10 to
form a barrier against corrosion.
[0042] The chemically-active glass compositions 100 provide added
protection for steel rods 10 used in RC structures. The glasses 100
may be used as the frit component in a reactive enamel formulation
for enhanced bond strengths between the concrete 40 and steel 10.
The glasses 100 contain relatively high concentrations of
P.sub.2O.sub.5 (typically between about 5 and about 20 weight
percent, more typically between about 9 and about 18 weight
percent), far in excess of the concentrations than used in the
conventional groundcoat compositions (typically about 0.5-1 weight
percent, see Table 1). In the present novel technology,
P.sub.2O.sub.5 is released as phosphate ions when attacked by a
corrosive aqueous alkaline solution. The released phosphate anions
react with calcium cations, and other constituents in the corrosive
environment, to form a stable hydroxyapatite (HAp) coating 110 on
exposed metal, such as steel reinforcing rods 10. This HAp coating
110 provides protection of the metal 10 against corrosion.
Representative compositions of phosphate-releasing glasses 100 are
given in Table 2. The glasses 100 are designated as `ARE-xP`
glasses, where `x` is a composition number, and `P` signifies a
phosphate-releasing composition. The coefficient of thermal
expansion (CTE) and dilatometric softening temperature for each
glass is also listed. These properties were determined by
dilatometry.
TABLE-US-00003 TABLE 3 Example compositions and selected properties
of phosphate-releasing glasses for reactive enamel coatings of
steel in RC structures wt % ARE-7P ARE-8P ARE-9P SiO.sub.2 41.5
41.9 41.7 P.sub.2O.sub.5 17.1 13.4 9.1 B.sub.2O3 8.3 10.4 13.8
Na.sub.2O 14.9 15.0 9.2 K.sub.2O 4.0 6.7 14.1 CaO 6.3 4.8 4.8
Al.sub.2O.sub.3 3.6 3.6 3.6 ZrO.sub.2 1.7 1.8 1.7 MnO.sub.2 0.0 0.0
0.0 MO 1.6 1.6 1.1 CoO 1.1 1.1 1.1 Soft. Temp (C.) 625 621 CTE
(ppm/C.) 16.5 13.1 logWt change (g/cm2-min)
[0043] Microscopic and spectroscopic analyses of the surfaces of
the steel 10 enameled with phosphate-releasing glasses, such as the
ARE-8P composition, as well as phosphate-free glasses, such as the
ARE-4 composition, show that the phosphate-releasing glass 100
provides enhanced corrosion protection to the steel 10, even in
regions where glass 100 did not initially coat the steel 10. For
example, micro-Raman spectroscopy revealed that holes 125 in the
ARE-8P enamel coating 100 of up to several hundred microns were
filled with HAp after 24 hours in Lawrence solution, a simulated
cement effluent, whereas only rust (iron oxide) was detected in
similar defects in an ARE-4 enamel on steel 10. Similar results
were noted when the same samples were exposed to a wet salt
environment.
[0044] In general, the glass coating 100 has a composition of
(100-x)(0.25Na.sub.2O.0.25B.sub.2O.sub.3.0.5SiO.sub.2).xP.sub.2O.sub.5
in mole percents,
where x is typically between about 5 and 15, more typically between
about 5 and 13, and still more typically between about 5 and 9. The
glass formulation typically includes small amounts of one or more
of the following oxides, most typically present in amounts of less
than about 6 mole percent: K.sub.2O, CaO, Al.sub.2O.sub.3,
ZrO.sub.2, MnO.sub.2, NiO, and/or CoO.
[0045] In operation, one or more (typically a plurality) steel
reinforcing members 10 are coated with phosphate-rich glass layers
100 for emplacement into a cementitious matrix. The respective
steel reinforcing members 10 have a first coefficient of thermal
expansion and wherein the respective glass layers 100 have a second
coefficient of thermal expansion, typically generally matched to
the first coefficient of thermal expansion. A cementitious matrix
40 is formed around each steel reinforcing member. Once placed into
the cementitious environment 40, phosphate is released from the
glass coatings 100. The phosphate reacts with the cementitious
material 40 to form a hydroxyapatite layer 110 on steel surfaces 10
without glass coatings 100. The glass coatings 100 typically have
compositions, in weight percent, of about 40-45% SiO.sub.2, 3-5%
Al.sub.2O.sub.3, 5-25% B.sub.2O.sub.3, 3-15% K.sub.2O, 5-25%
Na.sub.2O, 4-7% CaO, 1-2% ZrO.sub.2, 0-2% NiO, 0-2% CoO, and 5-20%
P.sub.2O.sub.5 and each coating 120 typically has a coefficient of
thermal expansion between about 12.5 and 13.5 ppm per degree
Celsius.
[0046] While the novel technology has been illustrated and
described in detail in the drawings and foregoing description, the
same is to be considered as illustrative and not restrictive in
character. It is understood that the embodiments have been shown
and described in the foregoing specification in satisfaction of the
best mode and enablement requirements. It is understood that one of
ordinary skill in the art could readily make a nigh-infinite number
of insubstantial changes and modifications to the above-described
embodiments and that it would be impractical to attempt to describe
all such embodiment variations in the present specification.
Accordingly, it is understood that all changes and modifications
that come within the spirit of the novel technology are desired to
be protected.
* * * * *