Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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COMPOSITION OF MATERIALS FOR PRODUCTION OF ACID
RESISTANT CEMENT AND CONCRETE AND METHODS THEREOF
FIELD OF THE INVENTION
This invention relates in general to compositions
and a method of use of such compositions to produce
cement pastes; mortars and concrete, which are resistant
to corrosion in an acidic environment.
BACKGROUND OF THE INVENTION
The acid corrosion of hardened cement and concrete
materials has drawn more and more attention recently due
to the corrosion of concrete sewer pipes and concrete
structures at municipal wastewater treatment plants,
chemical plants, coke ovens and steel plants. Further
the impact of animal feed and manure are of concern
regarding the acid corrosion resistance of concrete.
Conventional Portland cement concrete corrodes
relatively quickly in an acidic environment. Some
limited research results have indicated that the use of
supplementary cementing materials such as silica fume,
fly ash and ground blast furnace slag can improve the
resistance to acid attack of concrete. pH adjustment
and corrosion resistant linings are often used for
concrete sewer pipes and concrete structures at
municipal wastewater treatment plants at a substantial
additional cost.
A recent study conducted by Shi and Stegemann
entitled "Acid Corrosion Resistance of Different
Cementing Materials" and published in Cement and
Concrete Research, Vol. 30, No. 5, (2000) indicates that
the corrosion of conventional cementing materials in
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acid solutions depends on the nature of the hydration
products rather than the porosity of the hardened
cementing materials. Up to now, the widely held belief
has been that a high alkalinity of cement improves a
cement's acid corrosion resistance and improves the acid
neutralization capacity of the material. For example,
the USEPA Toxicity Characteristic Leaching Procedure
[Federal Register, 1986] examines the solubility of
metals upon addition of a limited amount of acid and is
usually used to evaluate the resistance of cement-
solidified wastes in an acidic environment. In fact,
passivation by deposition of reaction products plays an
important role in corrosion resistance and prevents the
matrix from further corrosion. Some cementing materials
may have low acid neutralization capacity, but high acid
corrosion resistance due to the passivation effect.
Acid resistant cement and concrete are well-known
in the art. Early acid resistant cements mainly
consisted of liquid sodium silicate, sodium
hexafluorosilicate as a setting agent for liquid alkali
silicate and ground quartz or silica flour as a filler.
In the past, sodium hexafluorosilicate was a readily
available by-product from production of phosphate
fertilizers. Now, however, it is difficult to
economically obtain this material due to changes in the
production of phosphate fertilizers. Other
disadvantages with presently known acid resistant
cements are that they exhibit low strength if cured at
temperatures over 35°C, the cement needs to be cured in
a dry environment instead of moist environment, and the
hardened cement does not show good resistance to water
or dilute acids unless an acid treatment is carried out
before being exposed to those environments.
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U.S. Patent No. 4,138,261 to Adrian et al.
discloses the use of condensed aluminum phosphates as
hardeners for liquid alkali silicates. U.S. Patent No.
4,482,380 to Schlegel discloses aluminum iron phosphates
as hardeners for liquid sodium or potassium silicate.
The hardeners have an atomic Al/Fe ratio of 0.052 to 95
and an atomic P/(A1+Fe) ratio of 0.9 to 3, and the
cement is waterproof 16 days after it is manufactured.
This patent does not discuss the acid resistance of the
cement. In fact, both condensed aluminum phosphates and
aluminum iron phosphates are very expensive. U.S.
Patent No. 4,221,597 to Mallow discloses the use of a
spray dried hydrated sodium silicate powder instead of
liquid sodium silicate for the manufacture of acid
resistant cement. However, it does not overcome any
disadvantages as mentioned above.
U.S. Patent No. 5,989,330 to Semler et al.
discloses an acid resistant cement composition composed
of a colloidal silica sol and an acid resistant
particulate aggregate without any setting agent. This
cement has to be pre-cured and is mainly suitable for
use as a mortar in acidic autoclave environments.
U.S. Patent No. 5,352,288 to Mallow discloses an
acid resistant cement comprised of, by weight, 1 to 1.5
parts of calcium oxide material containing at least
about 60~ CaO, 10 to 15 parts of pozzolanic materials
containing at least 30~ amorphous silica and 0.025 to
0.075 parts of alkaline metal catalyst. However, after
an immersion of the invented material in a 0.70 pH
sulfuric acid for two weeks, a white softened skin about
1/32" depth forms on the surface of the tested samples.
Setting agents, which are cheap, environmental
friendly, and technically sound are available. Such
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setting agents include powdered recycled glasses or coal
fly ash. Many cities in North American cannot find
applications for recycled mixed glasses, which are
mainly soda-lime silicate glasses, and must landfill all
or part of them. Coal fly ash is also widely available
at very low cost. Notwithstanding this, the prior art
does not disclose or even hint at the use of sodium-lime
silicate glasses as setting agents for liquid sodium
silicate. Furthermore, the prior art does not mention
improvements in moisture and high temperature curing of
acid resistant cement.
SUMMARY AND OBJECT OF THE INVENTION
In view of the foregoing limitations and
shortcomings of conventional concretes, there exists a
need to develop alternative acid resistant concretes
which use inexpensive and environmentally friendly raw
materials and can be cured at elevated temperatures.
More particularly, it is a purpose of this
invention to provide a method of manufacturing a cement
capable of resistance to water, dilute acid solutions
and strong acid solutions without any prior treatment.
A further objective of this invention is the
ability to cure cement pastes, mortars and concretes in
a moist saturated environment.
A further objective of this invention is the
ability to cure cement pastes, mortars and concretes in
moist conditions and at elevated temperatures to acquire
high early strength.
Yet another objective of this invention is to
provide an alternative which can use inexpensive
recycled materials.
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The aforementioned objectives are achieved by an
acid resistant cement in accordance with the present
invention.
Briefly, therefore, the invention is directed to a
type of cement which can be cured in steam at room and
elevated temperatures, is characterized by excellent
mechanical properties and is resistant to acid attack
corrosion. The cements according to the present
invention are composed of about 50 to about 100 parts of
liquid alkali silicate with a Si02 to Na20 or K20 ratio
ranging from 1.6 to 3.0, up to about 350 parts of
vitreous silicate as a hardener, together with up to
about 50 parts of lime containing material. Preferably,
up to 200 parts of inert filler, including ground silica
or ground ceramics are added to the formulation. Water
may be required to produce workable mixtures. The
amount of water utilized for a particular composition
and manufacturing procedure is readily determined by
routine experimentation. The hardened cement, mortar or
concrete can be cured in either dry or moist environment
at room or elevated temperatures, and can be contacted
by water or dilute acid without any pretreatment.
One of the important constituents of the cement of
the present invention, and which further distinguishes
it from prior art cements, is the use of lime containing
material serving as a property modifier. This
constituent may include hydrated lime, quick lime,
ground granulated blast furnace slag, ground steel slag,
or Portland cement. On one hand, these modifier
materials accelerate the condensation of liquid
silicates and act as a hardener for liquid water glass.
On the other hand, they improve the moisture and high
temperature curing properties of the cement, and enable
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the concrete to withstand direct contact with water and
dilute acid without any pretreatment.
With the forgoing and other objects, features and
advantages of the invention that will become hereinafter
apparent, the nature of the invention may be more
clearly understood by reference to the following
detailed description of presently preferred mechanical
embodiments of the invention and the appended claims
given for the purpose of disclosure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The essential materials in the present invention
are the liquid alkali silicate, setting agent and lime
containing material. An additional component such as
inert filler can be utilized.
The formulation of the present cement composition
includes liquid sodium or potassium silicate with a Si02
to Na20 or K20 ratio ranging from 1.6 to 3Ø A ratio
between 2.0 to 2.8 is preferred in this invention as
being a more practical commercial product and providing
adequate workability for the mixture. If the ratio is
too low, it may result in higher strengths, but the
hardened cement pastes, mortars or concretes have poor
resistance to acid attack. If the ratio is too high,
the viscosity of the liquid silicate and the formulated
mixtures increases, which affects the workability of
cement paste, mortar or concrete mixtures.
As used herein, the setting agent is vitreous
silicates, which include recycled glasses or coal fly
ash. Preferably, a waste material such as recycled
glasses is used. Preferred recycled glass are container
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glasses and plate glasses, which have at least 90~ of
their particles passing 100 Mesh.
Based on ASTM C618, coal fly ash is classified into
Class C and Class F categories. Fly ash belongs to
Class F if it contains greater than 70~ of the sum of
Si02+A1203+Fe203, and to Class C if it contains between
50% and 70°a of the sum of Si02+A1203+Fe203. Usually,
Class F fly ashes have a lower content of Ca0 and
exhibit pozzolanic properties, but Class C fly ashes
contain a high content of Ca0 and exhibit cementitious
properties. Since Class C fly ash has cementitious
properties, it can be used as a binder directly. Class
F fly ash is a pozzolanic material and possesses little
or no cementitious value but will, in the presence of
moisture, chemically react with calcium hydroxides at
ordinary temperatures to form compounds possessing
cementitious properties. In this invention, it is
preferred that a Class F fly ash with a carbon content
of less than 6~ be used.
The lime containing material should contain more
than 20~ CaO. It can be any one or a combination of the
materials such as blast furnace slag, steel slag,
Portland cement, cement kiln dust, quicklime or hydrated
lime. The use of these materials has also been found to
be important to the steam curing properties, and
resistance to water and dilute acid solution of the
product concrete.
Additional water may be required to produce
workable mixtures. The amount of water utilized for a
particular composition and manufacturing procedure is
readily determined by routine experimentation.
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Further illustrations of the characteristics and
practical advantages of the compositions described in
this invention are provided in the following examples:
EXAMPLE I
A batch of samples was made with 100 parts of liquid
sodium silicate (with a ratio of Si02 to Na20 of 2.58),
120 parts of ground recycled plate glass and 270 parts of
fine quartz sand. In another batch, 50 parts of ground
blast furnace slag was added in addition to those
materials described above. The dry materials were first
blended uniformly, and liquid sodium silicate was then
mixed with the dry blended material. No additional water
was added. The mixtures were cast into 2"x2"x2" cubes.
After 4 hours of still time in a sample preparation room,
the cubes with molds were placed into a heated dry
chamber for 15 hours of curing at 85°C.
At the end of the curing period, the cubes were
cooled to room temperature and demolded. Three cubes
from each curing chamber were tested for compressive
strength. Another six samples were immersed in water.
The results in Table 1 indicated that the addition of
ground blast furnace slag increased the strength of the
cement mortars significantly. After 28 days of immersion
in water, the strength of the first batch of the mortars
decreased to approximately 30% of the strength before
water immersion. However, the strength of the batch with
ground blast furnace slag did not show a significant
change in strength. This indicates that the addition of
ground blast furnace slag improves the water resistance
of the hardened cement mortars.
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Table 1
Effect of the Addition of Blast Furnace Slag on the
Strength of the Cement before and after Water Immersion
Batch Batch
1 2
Composition (Parts by weight)
Liquid sodium silicate (ratio of 2.58) 100 100
Ground recycled glass 120 120
Ground granulated blast furnace slag 0 50
Fine quartz sand 270 270
Compressive Strength (MPa)
After 15 hours of dry curing at 85C 36.0 54.4
Immersion in water 28 days after the
dry
X15 curing 13.1 52.1
EXAMPLE II
A batch with 65 parts of liquid sodium silicate
(with a ratio of Si02 to Na20 of 2.58), 80 parts of
ground recycled plate glass, 40 parts of ground quartz,
10 parts of ground granulated blast furnace slag and 270
parts of fine quartz sand was prepared. The dry
materials were first blended uniformly. Water was added
into the liquid sodium silicate and mixed uniformly:
Then, the diluted sodium silicate was mixed into the dry
blended material. The constituents of this batch are set
forth in Table 2.
The mixture was cast into 2"x2"x2" cubes. After 4
hours of still time in a sample preparation room, the
cubes with molds were placed into heated chambers for
curing. Some cubes were cured in a moisture chamber at
85°C, while others were cured in a dry chamber at 85°C.
A batch of conventional Portland cement mortars was also
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prepared and cured in the moisture chamber as a
reference.
After 15 hours of elevated temperature curing, the
test cubes were cooled to room temperature and demolded.
Three cubes from each curing chamber were tested for
compressive strength. The results in Table 3 indicate
that there is no significant difference in strength for
the cubes cured in dry or moisture conditions. Six steam
cured cubes were immersed in water, 10% H2S04 and 40%
H2S04 solutions. The change in mass of these cubes was
then monitored. After 28 days of immersion, the cubes
cured in water and 10% H2S04 solution showed a strength
decrease of 10% and 20%, respectively, while cubes in 40%
H2S04 solution did not exhibit any strength change.
Visual examination did not identify any deterioration on
the surface of any of these test cubes.
The weight of the test cubes immersed in water and
acid was monitored during the immersion test. It was
found that the weight of these acid resistance cement
mortar cubes changed less than 2% during the test in both
10% and 40% H2S04. However, conventional Portland cement
mortars dissolved completely after 2 weeks of immersion
in a 10% H2S04 solution. This means that the cement of
the present invention is resistance to acid attack.
Table 2
Composition (Parts by weight)
Ziquid sodium silicate (ratio of 2.58) 65
Ground recycled glass g0
3 0 Ground granulated blast furnace slag 10
Silica flour 40
Fine quartz sand 270
Water 15
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Table 3
Strength of Acid Resistant Cement Mortar Before and After
Acid Immersion
Compressive Strength (MPa)
After l5 hours of dry curing at 85°C 33.9
After 15 hours of steam curing at 85°C 31.1
Immersion in water 28 days after steam curing 28.8
Immersion in 10~ HZSO4 Solution for 28 days after
1 0 steam curing 24.0
Immersion in 40~ HZSO4 solution for 28 days after
steam curing 31.6
EXAMPLE III
r1 5
The objective of this example was to show the acid
corrosion resistance of concrete according to the present
invention. As set forth in Tables 4 and 5, test sample
preparation and curing of the concrete cubes was similar
20 to that described in Example II, except that coarse
quartz sand and quartz gravel was used instead of fine
quartz sand. It can also see that steam or dry curing
did not show a significant effect on the strength of the
concrete. After 28 days of immersion in loo H2S04
25 solution, both batches of cubes showed a slight increase
in strength. Visual observation did not identify any
deterioration on the surface.
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Table 4
Composition (Parts by weight)
Liquid sodium silicate (ratio of 2.58) 65
Ground recycled glass g0
Ground granulated blast furnace slag 10
Silica flour 40
Coarse quartz sand 241
Quartz gravel 362
Water 15
Table 5
Strength of Acid Resistant Cement Concrete Before and
After Acid Immersion
Compressive Strength (MPa)
After 15 hours of dry curing at 85°C 26.6'
After 15 hours of steam curing at 85°C 24.4
Immersion in lOg HZSO4 Solution for 28 days after 29.7
2 0 dry curing
Immersion in 10$ H2S09 solution for 28 days after 27.5
steam curing
The foregoing has described the invention and
certain embodiments thereof. It is to be understood that
the invention is not necessarily limited to the precise
embodiments described therein but variously practiced
with the scope of the following claims.
