Note: Descriptions are shown in the official language in which they were submitted.
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VOLUME-STABLE HARDENED HYDRAULIC CEMENT
Field of the Invention
This invention relates to improvements in the
composition of hydraulic cement. More particularly, it
relates to improvements in cement which consists of blends of
Portland cement~ calcium aluminate cement and a sulfate
compound, preferably of a calcium or aluminum sulfate or
gypsum.
Definitions
The term "hydraulic cement" as used herein is
intended to mean portland cements, expansive cements, air
entraining portland cements, pozzolanic cements, slag cement,
masonry cement, white portland cement, colored cement,
antibacterial cement, waterproof cement, refractory cement,
self-stressing cement, aluminous cement, and similar
materials.
The term "gypsum" as used herein is intended to
include gypsum such as is normally understood in the art.
This would include calcium sulfate (CaSO4) and its various
forms such as calcium sulfate anhydrate, calcium sulfate
hemihydrate, and calcium sulfate dihydrate, as well as
calcined gypsum, pressure calcined gypsum, and plaster of
Paris.
The term "aluminous cement" as used herein is
intended to include those cementitious materials normally
understood in the art to contain as the main cementitious
constituent, mono calcium aluminate (CaO x Al2~3). This
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would include high alumina cement (HAC), calcium aluminate
cement, and many other commercially available alumina
cements.
The term "Portland cement" as used herein is
intended to include those cements normally understood in the
art to be "Portland cement," such as thos~ described in ASTM
Standard C-150. The Portland cement component of these
cementitious mixtures acts to reduce drying shrinkage and
increase wet expansion. Other cements which act as drying
shrinkage inhibitors, although not specifically referred to
as Portland cement, are also suitable for use herein so that
the term "Portland Cement" should be understood as
encompassing those other cements. Examples of drying
shrinkage înhibitors include expansion promoters such as
expansive cements which are compatible with the other
constituents of the system.
BACKGROUND OF THE INVENTION
There have been numerous prior attempts at
providing cementitious systems to meet the needs of the
construction industry, particularly in the protection,
waterproofing, and repair of concrete stru~tures. The
optimum system should set within a relatively short period of
time into a hard mass or coating that has sufficient
strength, abrasion resistance, and corrosion resistance. It
is also highly desirable that these systems possess
impermeability to fluids, particularly aqueous solutions.
Also, such systems should not undergo excessive hardened
volume changes under either wet or dry conditions.
For commercial use, these types of cementitious
systems must also possess good bonding characteristics to
damp or dry surfaces, early as well as long term strength,
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and practical field worXability. They should be capable o~
withstanding freezing and thawing, as well as the action of
salts, solvents and other corrosive substances. Although
there have been a number of cementitious mixtures that
possess one or more of the above-described desirable
properties, none of the prior art to date has been able to
achieve all of the foregoing in one composition arld previous
attempts have had only limited success. U.S. Patent No.
4,357,166 discusses some of the limitations of these prior
art compositions in columns 2 and 3.
While mixtures of Portland cement, ~alcium
aluminate cement and gypsum have been in use for years,
various problems concerning their use have been encountered.
Previous compositions containing other hydraulic
cements such as aluminous cement and gypsum have been shown
to exhibit long term wet expansion. For e~ample, U.S. Patent
No. 4,357,166 discloses a cementitious composition which,
~hen mixed with water, is capable of setting rapidly to a
hard mass of high compressive strength without substantial
shrinkage during setting and which exhibits reduced wet and
dry volume change~ in the hardened state. That invention
also possesses a degree of impermeability to ~luids along
with abrasion, erosion, and chemical resistance, as well as
other characteristics which are desirable in a composition
having commercial usefulness in the construction industry.
The advantages of that invention are achieved by a
cementitious composition comprising a mixture of an aluminous
cement, a gypsum, a drying shrinkage inhibitor, and a wet
expansion inhibitor. The compositions of that invention
preferably use Portland cement as a drying shrinkage
inhibitor and a lithium salt as the wet expansion inhibitor.
However, various accelerators, retarders and other
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admixtures, when added to aluminous cement and gypsum
compositions, can significantly affect the haxdened volume
change (wet or dry), thus limiting their usefulness~
Additionally, previous attempts to blend yypsum
with other hydraulic cements, while produciny the desired
effect such as fast-setting or reduced shrinkage, have also
affected the hydraulic cement's soundness, durability,
workability, resistance to water or wet/dry cycling ~tability
or permanence of the resulting cement.
U.S. Patent No. 4,045,237 discloses a cementitious
composition which, when mixed with water, is capabla of
setting into a hard mass in a short period of time without
substantial shrinkage during setting and early hardening and
possessing a high degree of impermeability to fluids. The
composition comprises a particulate admixture of calcined
gypsum, high alumina cement and portland cement, or it may
comprise a mixture of particles of high alumina cement and
pressure calcined gypsum, without the use of Portland cement.
Portland cement consists mainly of tri-calcium
silicate and dicalcium silicate. To prepar~ this compound,
two types of raw materials are usually required - one high in
calcium content, such as limestone or chalk, and the other
2 rich in silica, such as clay or shale. These raw materials
ordinarially contain an appreciable concentration of iron~
bearing compounds. The presence of these compounds during
the heating process leads to the formation of a clinker
containing several percent of iron oxide.
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The structure of this Portland cement clinker will,
therefore, vary considerably due to variations in the
composition and particle size of the raw materials as well as
inconsistencies in the burning conditions, which leads to
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variations in clinker porosity as well as differences in
crystalline sizes and forms found in the aggregates of
crystallites.
Thus, the Portland cement component of the
cementitious compositions disclosed in U.S. Patent Nos.
4,357,166 and 4,045,237 contains an appreciable quantity of
iron oxide as described above~ In U.S. Patent No. 4,045,237
for example, it is critical to employ between 0.1-10% oE
Portland cement in the mixture. The addition of greater than
10~ of Portland cement leads to difficulties with the cement
hydration reactions due to the resulting proportion of ferric
oxide in the Portland cement-calcined gypsum-high alumina
cement mixture.
U.S. Patent No. 4,157,263, which is a division of
the application leading to the issuance of the '237 patent
discloses a method for using the compositions claimed in the
'237 patent for use in repairing and waterproofing concrete
structures and for filling voids and holes to form stable
underpinnings or foundations for machinery or heavy
equipment. The Portland cement utilized in the performance
of this method contains, as noted above, appreciable
quantities of ferric oxide, which restricts the amount of
Portland cement which may be added to the mixture, thus
reducing the strength of the composition.
Applicants have discovered that the hardened volume
changes which occur in concrete, grout, patching material and
water-proofing material made from blends of calcium sulfate
hemihydrate, calcium aluminate cement and Portland cement can
be reduced by using Portland cement containing reduced levels
of iron oxide. Applicants have further determined that such
a reduction of the iron oxide used in the Portland cement
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component dramatically increases the compressive strength of
this composition and improves its bonding capacity to
previously set concrete.
The maximum iron oxide content may vary, but as a
general principle it should be a maximum of about 2 weiyht
percent. Preferably, the iron oxide content should be as low
as possible, but as a practical matter, amounts lower than
o.1 weight percent are difficult to achieve.
SUMMARY OF THE INVENTION
This invention relates to improvements in the
composition of hydraulic cement. More particularly it
relates to improvements in cement which consists of blends of
Portland cement, calcium aluminate cement and a calcium or
aluminum sulfate compound.
The composition disclosed by the applicants
0 comprises from about 0.1 to about 80 parts by weight of a
Portland cement manufactured from raw materials containing
low levels of iron compounds so as to have a low iron oxide
content; from about 0.1 to about 40 parts by weight of a
sulfate compound, praferably gypsum, and from about 2 to
about 90 parts by weight of an aluminous cement. The most
advantageous composition includes about 2 to 20 parts by
weight of the low iron Portland cement, 55 to 95 parts by
weight of the aluminous cement and 2 to 10 parts by weight of
gypsum.
While any sulfate compound can be used in this
invention, organic or inorganic sulfate salts are preferred.
Calcium sulfate provides the best results and is the most
advantageous whe-ther used as a pure chemical, formed in situ,
or added in its common form, gypsum. Aluminum ammonium
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sulfate (AlNH4(S~4)2) and aluminum potassium sulfate (AlK
(so4)2) also provide good results. Other alkali metal
sulfates have not been found to be useful, and satisfackory
performance is found only with the calcium and/or aluminum
sulfates. Due to its availability, gypsum in any of its
various forms, is most advantageous sul~ate compound.
Ik is also possible to form the most preferred
compound, calcium sulfate, in situ, by reacting a mixture of
sodium sulfate with calcium nitrate, for example. Other
calcium compounds which react with various sulfate salts can
be used.
In one embodiment of the cementitious composition,
the maximum iron oxide content of the Portland cement is 2
weight percent, measured as ferric oxide according to ASTM
test method C-114. In a further embodiment the gypsum
selected for use in applicants' composition is calcium
sulfate hemihydrate.
Applicants' composition may further ~omprise a
number of additional ingredients and additives, which may
include up to about 90% by weight of an aggregate based upon
a total weight of Portland cement, sulfate compound and
aluminous cement in the composition. Additional ingredients
may include a compound capable of generating a volume of gas
upon contact with water, a surface active agent, a water
reducing agent and a set time controlling agent.
Applicants' volume-stable cementitious composition
therefore comprises from about 0.1 to about 80, and
preferably 2 to 20, parts by weight of a Portland cement
having a maximum iron oxide content of 2 weight percent; from
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about O.l to about 40, preferably 2 to lO, parts by weight of
a sulfate compound and from about 2 to about 95, pre~erably
55-95, parts by weight of an aluminous cement.
Applicants have also discovered a novel method Por
producing their volume-stable cementitious compo~ition which
comprises blending, for a prefletermined duration, a mixture
comprising from about O.l to about 80 parts by weight of a
Portland cement manufactured from raw materials containing
low levels of iron compounds so as to contain less than about
2% of iron oxide; from about O.l to about 40 parts by weight
of a calcium or aluminum sulfate compound and from about 2 to
about 90 parts of weight of aluminous cement, and thereafter
hydrating this mixture with water.
The method developed by the applicants may include
several additional steps, which include adding to the mixture
an amount of from about l to about ~0 parts by weight of an
aggregate based upon the total weight of Portland cement,
sulfate compound and aluminous cement befor~ hydrating the
mixture with water. In addition, one may also add to the
mixture at least one of an accelerator, a retarder, a
pigment, a water reducer or a gas generating agent.
The product produced by practicing the method
disclosed herein by the applicants is also novel and should
be considered part of their invention.
The improvement in the cementitious composition
disclosed by applicant comprises controlling the maximum iron
content of the Portland cement to about 2 weight percent in
order to obtain improved volume stability, higher strength
and better bonding strength to other cementitious
compostionsO The improvement further comprises decreasing
the setting time for the composition by reducing the iron
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oxide content of the cement to as low a value as possible.
The iron oxide content should range between O.l and 2 weight
percent in applicants' composition~
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following examples are present~d for the
purpose of illustrating, without limitation, the nov~l
cementitious composition of the invention and the advantages
thereof. In the examples, parts and percentages are by
weight unless otherwise indicated.
EXAMPLE 1
A composition comprising calcium aluminate cement,
calcium sulfate hemihydrate and portland cement wherein the
portland cement was manufactured from compounds containing a
"normal" amount o~ ferric oxide, about 23 weight percent, is
utilized.
The following ingredients were dry blen~ed for one
minute:
Substance Weiqht Percent
Portland cement 8
Calcium aluminate cement 25
Calcium sulfate he~ihydrate 5
*Dried ~luid Coke 3
Melment F-lO 0.5
Lithium Carbonate 0.09
Citric Acid 0~12
Sand ~.29
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* Trade-mar~
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After dry mixing, 12.5 parts of water were added to
hydrate the mix, and the following characteristics were
determined:
TimeCompressive Stren~th
1 hour 900 psi
3 hours 3,000 psi
~4 hours 6,300 psi
Shrinkage and expansion tasts were performed on a
hardened 11 inch bar cast from the composition:
Dry shrinkage = 0.0196% after 14 days
storage at 50% humidity
Wet expansion = 0.0130% aft~r immersion in water
EXAMPLE 2
The same components as found in Example 1 were
utilized in the same proportions. In this example, however,
the Portland cement was manufactured from raw materials
containing low levels of iron compounds, and contained 0~4
weight percent of ferric oxide.
The following improvements over the values from
Example l were noted after hydration of the compositiono
Time Compressive Stren~th
1 hour 4,500 psi
3 hours 9,000 psi
24 hours 11,000 psi
Dry shrinkage = 0.0003% after 14 days
storage at 50% humidity
Wet expansion = 0.0004% after immersi~n in
water
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A 50% increase in bonding strength over the
composition as described in Example 1 was also noted as well
as a drastic decrease in the water absorption and
permeability of the hydrated product.
Examples 3 and 4 further show the improvement that
low iron oxide Portland cemenks provide.
In Example 3, the following ingredients were dry blended for
one minute:
EXAMPLE 3
Substance Weight Percent
Portland cement 8
Calcium aluminate cement 25
Calcium sulfate hemihydrate 5
Dried fluid coke 3
20 Melment F-10 0.5
Sand 58.5
As in Example 1, the Portland cement contained about 23
weight percent ferric oxide. A~ter dry mixing, 12.5% water
was added to hydrate the mix and the following
characteristics were determined:
Time Compressive Streng~h
3 hours 975 psi
24 hours 8,525 psi
7 days 9,500 psi
Dry shrinkage = 0.0736% after 28 days storage at 50% relative
humidity
Wet expansion = Could not be determined because the bars
would destruct when immersed in water.
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EXAMPLE 4
The components used in Example 3 were once again ukilized in
the same proportions. In this example, however, the Portland
cement was manufactured from raw materials containing low
levels of iron compounds as in Examples 2 (i.e., a ferric
oxide content of 0.4 weight percent).
The following improvements over the values from
Example 3 were noted after hydration of the composition:
Time Compressive Strength
3 hours 5,750 psi
24 hours 8,925 psi
7 days ll,O75 psi
Dry shrinkage = 0.04% after 28 days at 50% relative humidity.
Wet expansion = 0.0073% after 28 days immersion in wate.r.
While any gypsum can be utilized in these
formulations, calcium sulfate hemihydrate has been found to
provide the most effective results. The Melment F-l0
compound used in the e~amples, is a well-known water reducing
agent which is available from American Admixtures, Chicago,
Illinois. Other water reducing agents can also be used in
this invention.
In addition to the three essential components of
the cementitious composition of this invention, the normal
additives that are added to concrete can, of course, be used.
These include, but are not limited to, accelerators,
retarders, pigments, air entraining agents, water reducers,
pumping aids, fly ash, gas generating and releasing agents
and, of course, the full range of aggregates.
While it is apparent that the invention disclosed
herein is calculated to provide an improved cementitious
system over those described in the prior art, it will be
appreciated that alternate embodiments may be devised by
those skilled in the art. It is therefore intended that the
appended claims cover all modi~ications or embodiments as
fall within the true spirit and scope of the present
lnventlon .
