Note: Descriptions are shown in the official language in which they were submitted.
9 ~ 1
Background Of The Invention
The present invention is directed to a cement admixture
capable of greatly increasing the fluidity of cement
compositions without retarding set or causing air entrainment
therein.
Hydraulic cement compositions are brought into a
workable form by mixing the components with an amount of
water which is greater than that required to hydrate them.
The mixed mineral binder composition is poured into a form
and allowed to harden at atmospheric temperature. During
the hardening, the excess water remains, leaving cavities in
the formed structural unit and, thus, reduces the mechanical
strength of the resultant unit. It is well known that the
compressive strength of concrete structures generally bears
an inverse relationship to the water-cement ratio of the
unset mix. The desire to use smaller quantities of water is
limited by the required workability of the uncured mixture.
Cement admixtures are known which are capable of
reducing the viscosity of unset cement-water suspension to
provide a suspension which is more manageable. It is
desired in many structural applications to have the cement
composition be of low viscosity or even self-levelling
while, at the same time, to be capable o~ forming a set
cement of high compressive strength (via low water-cement
ratio). The flooring for buildings and industrial
construction represent fields of application where
considerable savings of cost and time could be obtained by
using a cement composition having superior flow properties.
There are presently avail~ble, various admixtures which
are known to cause the above described viscosity reducing
characteristics. These materials are generally known as
water-reducing agents such as lignin sulfonates and
polysaccharides and superplasticizers such as sulfite
~ if ?d condensation products of melamine-formaldehyde or
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naphthalene-formaldehyde. Fluidizing agents are normally
categorized as water-reducing agents if they are capable of
only modifying viscosity to a very limited degree. These
materials normally also have the disadvantages of retarding,
if not preventing, set time, increasing air content and
permitting only moderate reduction in water. Fluidizing
agents which have the ability to permit large water cuts in
the cement mixture, while maintaining fluidity or permit
large increases in fluidization for a constant water
content, are known as superplasticizers. These materials
should also permit increased streng~h of the cement
composition after 24 hours of set and not retard set.
Japanese Patent Publication 51-525 discloses that
sulfonated polystyrenes of any molecular weight can act as a
fluidizing agents for cements as long as it has sufficient
sulfonate groups to be hydrophilic. U.S. Patent 4,076,699
specifically directs one to use polystyrene sulfonates which
are of very low molecular weight, preferably with a degree
of polymerization of less than 50. Generally, the
polystyrene materials have not been widely used because they
are thought to impart only a low degree of fluidity to
cement composition and, in addition, they may cause air
entrainment in the treated cement composition.
Recently, ~. P. Preiss and H. R. Sasse compared, in
Super~lasticizers in Concrete, Vol. II, Ed. by
V. M. Malhotra et al. pages 733-750, the fluidity effect of
various fluidizing agents. Specifically, sulfonated
melamine formaldehyde condensates, sulfonated naphthalene-
formaldehyde condensates, lignin-sulphonate and a dispersible
polystyrene were compared. The study teaches that, of all
of the materials tested, the polystyrene admixture gave the
poorest performance and further concluded that very high
dosages of any of the studied admixtures are needed to
appreciably increase the flow of a cement composit.o
It is highly desired to have a fluidizing admixture
which can impart a high degree of fluidity to a cement
composition, is capable of achieving this result at low
dosages and is capable of achieving this result without
adverse effect of increased air entrainment or set
retardation.
Summary Of The Invention
The present invention provides a method of providing a
high degree of fluidity to cement compositions at low dosage
rates. Further, the present invention is directed to a
superplasticizer admixture capable of providing a high
degree of fluidity to cement compositions without causing
air entrainment or set retardation therein.
The present invention is directed to the utilization of
a superplasticizer for cement compositions comprising an
alkali or alkaline earth metal salt of a sulfonated poly-
styrene having a degree of polymerization of from lS0 to 675.
Detailed Description Of The Invention
It has been presently found that an unexpectedly high
degree of fluidization can be imparted to cement
compositions by having the composition contain small dosages
of an alkali or alkaline earth metal salt of polystyrene
sulfonate. The polystyrene sulfonate must have a degree Gf
polymeriæation of from 150 to 675. The greatest degree of
fluidization per unit dosage can be attained with polymer
having a degree of ~olymerization of from 150-300.
! Cement compositions capable of being modified by the
subject admixture are conventional cement based compositions
formed by mixing standardized amounts of required components,
i.e. a hydraulic cement, water, sand and aggregate, as is
applicable for the particular material belng formed.
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The cement compositions in which the present admixture
has been found useful include cement pastes, that is,
mixtures composed of a hydraulic cement and water, mortars
composed of hydraulic cement, water and sand in standard
amounts; and concrete compositions composed of a hydraulic
cement, water, sand, and aggregate, each in standard amounts
and size. The present invention is of particular use in
concrete composi~ion normally used to form structural units.
The cement component in the presently treated cement
compositions are hydraulic cements, such as, for example,
portland cement. These cements are conventionally known and
are manufactured by calcininy a mixture of limestone and
clay to form a clinker, and by grinding the clinker to a
fine powder. The major compounds found in portland cement
are tricalcium silicate, dicalcium silicate, tricalcium
aluminate, and tetracalcium alum:inoferrite. The tricalcium
and dicalcium silicates are thought to be the principal
bonding constituents in the port:land cement. Tricalcium
silicate, when mixed with water, forms a calcium silicate
~0 hydrate known as tobermorite gel and calcium hydroxide. The
dicalcium silicate, when contacted with water, forms similar
products, but at a much slower rate of reaction. The
tricalcium silicate, having the greater rate of reaction,
determines to a large extent the rate of set of the cement.
To provide materials which are suitable for different uses,
portland cements having a range of properties have been made
commercially available. Four general types of portland
cements, varying principally in the relative quantities of
tricalcium silicate and dicalcium silicate present therein,
are commonly produced. The proportions of the principal
compounds present in three of these cements are shown in
Table I.
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TABLE I
Cement Type . . . . . . . . . O . . . . . .I II III
Composition, wt. percent:
Tricalcium silicate . . . . . . . . . 53 47 58
Dicalcium silicate . . . . . . O . . 24 32 16
Tricalcium aluminate . . . . . . . . 83 8
Tetracalcium aluminoferrite . . . . . 8 12 8
..... . . .. _ _ _
The water to cement ratio of a particular composition
will determine, to a large extent, the strength of the
resultant set material. As discussed above, the amount of
water required to form a uniform composition is in excess of
that needed to react with the cement components. Reduction
of the water to cement ratio whiIe maintaining or increasing
the fluidity of the mixture is highly desired. When using
the presently described admixture, one has greater
capability of forming a uniform mixture, of molding the
cement composition into desired shapes, of causing the
composition to be substantially self-leveling and of causing
the cured cement composition to exhibit higher compressive
strength for the same amount of cement. The term
"fluidizing agent" as used herein is directed to agents
capable of maintaining the fluidity oE a cement composition
while reducing the water content of the composition or to
increase the fluidity of a cement composition formed with a
set water-cement~ ratio. The term "superplasticizer" as used
herein de~ines materials capable of imparting fluidizing
properties described above to a higher degree. Unlike known
fluidizing agents generally, the presently described
superplasticizer agents have been unexpectedly found to
impart fluidity and to increase the mechanical strength and
workability of a cement composition to an exceptionally high
degree at very low dosages.
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It has been presently unexpectedly found that certain
specific metal salts of polystyrene sulfonate are capable of
imparting a high degree of fluidity to a cement or concrete
composition. These materials are alkali and alkaline earth
metal salts of sulfonated polystyrene haviny a degree of
polymerization of from 150 to 675. Polymeric materials
whlch are outside of this D.P. range, exhibit a
significantly lower effectiveness as a fluidizing agent.
The subject sulfonated styrene polymers can be formed by
conventional techniques well known to the artisan. The
styrene monomer is first normally polymerized to the proper
degree of polymerization. The resultant polymer is
sulfonated and then neutralized. ~tyrene monomer can be
polymerized by conventional processes capable of forming
polystyrene to a degree of polymerization of 150 to 675.
While conventional ~ree radical polymerization may be
employed to form the desired polymer, it is preferred that
conventional anionic polymerization techniques be used to
form the polystyrene in order to provide a polymer of the
proper average degree of polymerization and of a narrow
range of molecular weight. Anionic polymerization of
styrene monomer is performed by introducing an initiator to
a monomer containing solution. The initiator ~an be any
anionic initiator such as an organolithium compound, as for
example, butyllithium, phenyllithium and ~he like or a
Grignard reagent or other organometallic compound known to
act as an anionic polymerization initiator. The styrene is
normally dissolved in an organic solvent which is inert to
the initiator. It is preerred that the solvent be an ether
as, for example, tetrahydrofuran. The organometallic
initiator, is taken up in an organic hydrocarbon solvent
such as hexane or benzene, and is introduced into the
polymerization zone in an amount suitable to cause the
desired deg~e~e of polymerization. It is readily understood
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that the degree of polymerization is inversely proportioned
to the ratio of initiator to monomer. The polymerization is
usually run under an inert atmosphere and at low temperatures
such as ambient temperature or below with temperatures oE
from 0C to -78C being suitable. After completion of the
reaction, the formed polymer is isolated by evaporating off
the solvent. The polymer is washed with water to free it
from the metal salt by-product. The exact amounts and
concentration of monomer, initiator, etc. to form polymer
10 product required for use in the present invention are
readily determined.
The resultant polystyrene having a degree of
polymerization of from 150 to 675 and preferably from
150 to 300 is then sulfonated. The polystyrene can be
treated in ~he reaction media used for the polymerization or
it can be isolated and then redissolved in an organic solvent ?
such as a halogenated alkane. The sulfonating agent can be
any conventional acid sulfonating agent such as oleum, SO3,
concentrated sulfuric acid, chloxosulfonic acid and the like.
20 The degree of sulfonation should be at least suEficient to
cause the polystyrene to be hyd~ophilic. Usually the degree
of sulfonation should be at least 0.5 sulfonate units per
styrene unit~ The sulfonated product is neutralized with an
alkali metal or alkaline earth metal basic material such as
sodium hydroxide, calcium hydroxide, calcium oxide, and the
like. The salts of sodium and calcium are preferred.
The polystyrene can contain minor amounts of styrene
derivative comonomer, such as alpha-methyl styrene, vinyl
toluene, vinyl xylene and the like. The comonomer should
30 not be present in greater than 10 percent of the monomer
units in the polymer.
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The formed salt of sulfonated polystyrene having a
degree of polymerization of from 150 to 675 can be added to
a cement or concrete composition in any manner which causes
substantially uniform distribution therein. The subject
agent can be added to the cement mixture in a dry state or
as an aqueous solution. Small amounts of from 0.01 to
5 weight percent and preferably from 0.1 to 2 percent of the
subject admixture based on dry weight of cement will
increase the fluidity sufficiently for most purposes.
The use of the subject salt of sulfonated polystyrene
having the particular degree of polymerization of from
150 to 675 have been found to impart an unexpected high
degree of fluidity to cement and concrete compositions in
comparison to equal amounts of other known fluidizing agents
including sulfonated polystyrenes of low D.P. as
specifically suggested by the prior art. Further, the
subject has been found not to cause entrainment of air in
the treated cement composition as is a problem with known
fluidizing agents such as low D.P. sulfonated polystyrene.
Finally, the present material has the unexpected advantage
of not causing appreciable retardation of set of the cement
composition as is imparted by the use of other fluidizing
agents as discussed above.
The following examples are given for illustrative
purposes only and are not meant to be a limitation on the
subject invention except as made in the claims appended
hereto. All parts and percentages are by weight unless
otherwise indicated.
EXAMPLE I
Commercially obtained sodium polystyrene sulfonates
(sold as a gas permeation chromatography standard) was
used. The polymer was monosulfonated to nearly lO0 percent
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~ 1623~3
and was prepared from polystyrene of narrow molecular weight
distribution (MW/Mn = 1.1) formed by anionic
polymerization.
0.25 part of the above described commercially obtained
sodium polystyrene sulfonate having a D.P. of 167 was mixed
with 100 parts of Type II portland cement and then with
sufficient water to give a water-cement ratio of 0.45. The
resultant composition was tested for fluidity using a Mini-
Slump Flow Test procedure as described by L. M. Mayer and
W. F. Perenchio in Concrete International~ Vol. 1, No. 1,
page 36ff (January 1979).
The material exhibited exceptionally high flow
properties of 163+2 mm on duplicate samples.
EXAMPLE II
The process and procedures described in Example I were
repeated except that the sodium polystyrene sulfonate was a
commercially obtained polymer similar to that described in
Example I formed from polystyrene having a D.P. of 475
(MW/Mn = 1.1).
The results of the Mini-Slump Flow Test showed that
exceptionally hi9h flow properties of 153 mm can be obtained
using very small dosages.
EXAMPLE III
The process and procedures described in Example I above
were again repeated except that the sodium polystyrene
sul~onate was formed from a commercially obtained polystyrene
sulfonic acid (sold as a conductive film former and as scale
inhibi~or for aqueous circulation systems) (Versa-TL 121)
which has about 0.9 sulfonic acid units per styrene unit.
The acid was neutrali2ed with NaOH The D.P. of the polymer
, was 650.
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The polymer was used as a cement admixture in the manner
described in Example I and the resultant cement composition
was tested for flow properties as described in Example I.
The results showed that exceptionally high flow properties
of about 150 mm can be obtained with very small dosages.
EXAMPLE IV
For comparative purposes as a standard, a cement
composition was formed from a Type II cement in the same
manner as described in Example I above except that the
cement composition was free of polystyrene sulfonate. The
cement was mixed with water to give a uniform composition
(water/cement = 0.45) which was tested for fluidity using
the Mini-Slump Flow Test described in Example I above.
The composition exhibited a flow of 70 mm.
EXAMPLE V
For comparative purposes, a commercially available
naphthalene-formaldehyde sodium sulfonate material
(Daxad-15) commonly used as a cement superplasticizer
was used in place of the subject polymer in the manner
described in Example I. The flow properties of the
~reated cement composition was about 122 mm.
EXAMPLE VI
This example is made for comparative purpose with
reference to the preferred materials of U.S. Patent
4,076,699. A commercially obtained sodium salt of a
sulfonated polystyrene having a degree of polymerization
of 22 (~ /Mn = 1.1) and formed in the same manner as
described in Example I above was tested for fluidity.
The material had a molecular weight substantially the same
as the resin of Example I of U.S. 4,076,699.
The material was mixed with Type II hydraulic cement in
the same manner as Example I and tested for fluidity using
the Mini Slump Test. The material exhibited a flow of only
112 mm.
A sample was formed in the same manner as described
above except that the sodium sulfonate polystyrene had a
D.P. of 34. The ma~erial exhibited a flow of only 123 mm.
EXAMPLE VII
This is a comparative example illustrating the fluidity
10 properties of high molecular weight material as covered by
the illustrative examples of Japanese Publication 51-525.
A cement composition was prepared in the same manner as
in Example I above except that the subject polystyrene
sulfonate was substituted with a commercially obtained sodium
polystyrene sulfonate having a D.P. of 5400 (MW = 106
based on free acid). The flow of t:he cement was only 80 mm.
While the invention has been described in connection
with certain preferred embodiments, it is not intended to
limit the invention to the particular forms set forth, but,
20 on the contrary, it i5 intended to cover such alternatives,
modifications and equivalents as defined by the appended
claims.
