Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
It is well known that dispersing agents are useful
additives to cementitious materials and especially Portland
cement. By more effectively dispersing the cement paste,
the aggregate particles, reinforcement, fillers, pigments,
or other ingredients of the final mixture are more homo-
geneously coated and the resulting concrete product has more
compressive strength. Because the dispersing agent does not
function to increase adherence as one of its prime pro-
10 perties, the resulting concrete with the dispersing agentalone does not generally show an improvement in internal ad-
herence or in adherence to adjacent material; and accord-
ingly, the flexural strength of the resulting concrete is
not increased. Further, outside of some relatively minor
increase in density due to the greater homogeneity, pene-
tration or resistance to absorption of liquids is not
achieved by the use of a dispersing agent alone.
Latexes are also well-known additives for use with
cementitious materials and Portland cement mortar mixtures.
20 Latexes of rubbery polymers are known to provide greater
continuity throughout the mixture and thus a greater ad-
herence within the mixture as well as adherence to adjacent
materials. It is thus known that the use of latex does pro-
vide an increase in the flexural strength of concrete when
it is an additive to the cement mixture. It also provides
greater plasticity and workability to the mixture, and a re-
duction in the viscosity of the mixture, permitting a re-
duction of the water to cement ratio. The rubber film
forming latex extends throughout the cured concrete and
30 appears to reduce the penetration and increase the resist-
ance to absorption o liquids, sspecially corrosive salt
solutions. This is extremely beneficial when the cement
mixture is used for concrete pavements by reducing the
amount of attack caused by the salts used for ice and snow
prevention or removal.
U.S. Patent 3,677,780 illustrates the use of a
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beta-naphthalenesulfonic acid-formaldehyde condensate as an
additive to cement to obtain increased compressive
strength. The patent teaches that the use of the additive
has an even greater effect in increasing compressive
strength than the mere reduction of the water cement ratio~
However, there is no disclosure whatsoever of the use of a
latex as an additional component to the cement mortar mix-
ture.
Reissue Patent 28,722, reissued February 24, 1976,
discloses the use of about 5-25~ based on the weight of
Portland cement of a styrene-butadiene copolymer latex, and
a combination of three surfactants, one anionic, one non
ionic and a polyorganosiloxane.
U.S. Patent 2,662,064 shows a cementitious pumpable
coating composition including cement, both a fibrous filler
and a non-fibrous filler, a stabilized latex, and a water
soluble thickener. The requirement of a thickener causes an
interference to the curing action of the cementitious mater-
ial being used and would defeat the purposes of the feas-
ibility of the present invention. The lowest amount oflatex disclosed is an amount equal to the amount of dry
cement, and this proportion of latex would not result in a
workable concrete for the purposes of the present invention.
SUMMARY OF THE INVENTIO_
It has been found that an improved cement mortar
composition, especially a composition comprising Portland
cement, aggregate and water useful in thin sections such as
bridge overlays and the like may be provided which comprises
additionally a latex of a styrene-butadiene containing poly-
30 mer and a dispersing agent which in combination increase thecompressive strength and the flexural strength of the cured
cement mortar, permit a reduction in the amount of water and
provide a plastic flowable mix. The concrete is believed to
have greater freeze-thaw stability and the penetration by
moisture and corrosive salt solutions is believed to be
reduced.
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The preferred latex additive is a styrene-butadiene
containing polymer having a styrene to butadiene ratio of
from about 40:60 to about 70:30, and the preferred dis-
persing agent is a polymerized or condensed alkyl sub-
stituted or unsubstituted naphthalene sulfonic acid, partic-
ularly the sodium salt thereof.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to the improvement of
cementitious compositions and while it will be described in
lO connection with Portland cement mortar compositions it will
obviously be equally applicable to provide improved com-
positions using gypsum, plaster of paris and other
cementitious materials.
The cement composition of the present invention
will provide concrete using a lower water:cement ratio and
having higher compressive strength and higher flexural
strength. It is believed that this concrete will also have
greater freeze-thaw stability, reduced penetration by
moisture and corrosive salt sol- utions, and a reduced
20 tendency to leaching and/or efflor- escence. Such a
concrete is highly useful for the paving of thin concrete
sections found in bridge deck overlays, over- passes, ramps,
elevated sections of freeways, and the like. For this work
it is desirable to use a non-air entraining Portland cement
denoted in the trade as type I or II con- forming to the
requirements of ASTM C 150 for Portland cement.
In addition to the cementitious material, it is
customary to use a mineral aggregate, examples of which are
sand, limestone, and gravel. Generally, it is desirable for
30 the sand to conform to the requirements of ASTM C 33 for
concrete sand. The total amount of aggregate used for this
type of concrete is normally from about 3.0 to about 5.0
parts by weight, preferably from about 4.0 to about 4.5
parts, of aggregate per 1 part by weight of Portland cement.
The first of the combination of 2 additives making
up the present invention is a latex of a polymer. Suitable
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polymers include styrene-butadiene containing polymers,
preferably styrene-butadiene polymers, more preferably
styrene-butadiene polymer containing a minor amount of
N-methylolacrylamide, and most preferably styrene-butadiene
polymers containing minor amounts of acrylonitrile and
N-methylolacrylamide, the amount of polymer in the latex not
being critical but desirably from about 25 to about 60 per
cent by weight. Further, the ratio between the styrene and
butadiene content of the polymer is a relatively critical
lO factor. The amount of styrene content serves to add
strength while the butadiene content provides the rubbery
and flexural properties and it is necessary to obtain the
right balance in order to obtain a suitable commercial pro-
duct. A styrene-butadiene containing polymer having a
weight ratio of styrene to butadiene within the range of
from about 40:60 to about 70:30 is desirable and a par-
ticularly desirable range in the styrene to butadiene ratio
runs from about 60:40 to abut 67:33. At a styrene content
in the polymer above about 70% a dried film derived from the
20 latex has substantially lost its rubbery texture and becomes
a more brittle film. For the purposes of the present in-
vention, the styrene content needs to be sufficiently high
to provide the increased strength properties but at the same
time adequate butadiene content must be provided so that the
dry polymer film has a rubbery texture. The amount of
N-methylolacrylamide in styrene-butadiene polymers con-
taining a minor amount of this monomer is from about 0.5 to
about 5.0 parts, preferably from about 1.0 to about 3.0
parts, by weight of the polymer. The amounts of acrylo-
30 nitrile and N-methylolacrylamide in styrene-butadiene poly-
mers containing minor amounts of both of these monomers each
are from about 0.5 to about 5.0 parts, preferably from about
1.0 to about 3.0 parts, by weight of the polymer. The total
amount of both monomers is from about 1.0 to about 6.0
parts, preferably from about 2.0 to about 5.0 parts, by
weight of the polymer.
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In the cement mix, it is desirable that the polymer
component of the latex be present in an amount from about 1
to about 15 parts by weight per 100 parts by weight of
cement - i.e. is based on the polymer content of the latex,
which is known from the solids content thereof, and not
based on the latex per se. Hereinafter, this weight of
polymer is referred to as being on a dry weight basis. It
has been found that when the polymer addition for this type
of latex is greater than about 15 parts the resultant
lO strength of the cured concrete diminishes very rapidly.
The dispersing agent is another critical component
of the present invention. It is desirable to use a polymer-
ized or condensed alkyl substituted or unsubstituted
naphthalene sulfonic acid or salt thereof. One such product
is sold under the trademark DAXAD 11 by W. R. Grace and
Company. Another such product is sold under the trademark
LOMAR D by Diamond Shamrock Corporation. There are several
similar types of such dispersing agents available. When the
dispersing agent is a sodium salt of a condensed mono
20 naphthalene sulfonic acid, better results are obtained.
This component is added to the cement mix in an amount of
from about 0.5 to about 8 weight per cent of the latex on a
dry weight basis, with a particularly preferential rate
being from about 3 to about 4 weight per cent. It is im-
portant that there be no carboxylation of either the latex
or the dispersing agent. Test work has shown that if there
is any carboxylation, the improvements to the mortar mixture
are deteriorated by some action not presently understood.
The making of the improved cementitious mortar mix-
30 ture is not a critical part of the present invention. Inaccordance with the general practice, the cement and ag-
gregate materials are mixed together and stirred or agitated
in a normal cement mixer in their dry or semi-dry condition
for approximately 5 minutes. After this, the latex, dis-
persing agent and water are combined and added. Mixing is
continued until a smooth, homogeneous mixture is obtained.
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In connection with the water, care must be taken to deter-
mine the water content of the aggregate prior to its use so
that the additional water added is minimal. The present in-
vention contemplates that the weight ratio of water to
cement for best results be maintained within the range of
from about 0.3:1 to about 0.4:1 and preferably within the
range of from about 0.3:1 to about 0.35:1. Obviously, the
amount of water added controls this water:cement ratio and
it is desired that it be maintained at this relatively low
level. An acceptable slump of from about 4 to about 7
inches may be obtained for mortar mixes using this
water:cement ratio.
To illustrate the present invention, cement/mortar
mixes were made and tested as described in the Examples
which follow.
EXAMPLE 1
This Example compares the properties of Portland
cement mortar mixes without either additive and mixes with
20 both additives. Samples A, B and C were made up using the
formulations shown in Table I using the procedure described
hereinabove. The water content of all of the components was
predetermined and an additional amount was added to give the
total water content in parts by weight shown in Table I.
All other parts shown are by dry weight. Sample A served as
a control and contained no latex and no dispersing agent.
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TABLE I
SAMPLE
A B C
Portland Cement (Type II non-air
entraining 16.6 16.7 16.8
Limestone (0.75 inch, washed) 31.3 31.5 31.6
Sand 43.1 43.4 43.5
Total water content 9.0 5.85 5.5
Latex 1. 0 2.52 2.52
lO Dispersing Agent 2- 0.08
1. Aqueous latex of a 66:34:2:2.5
styrene-butadiene-acrylonitrile-N-methylolacrylamide
polymer, with pH = 9.4 and 47 percent solids
content.
2- Sodium salt of a condensed mono naphthalene
sulfonic acid sold under the tradename Lomar D by
Diamond Shamrock Corp.
Test specimens of concrete were prepared from each
of Samples A, B and C. Slump was measured according to ASTM
C 143. Air content was measured using a Forney air pressure
meter available from Forney's Incorporated, using the in-
structions supplied with the instrument. The water:cement
ratio was the weight ratio of total water content to
cement. Compressive strength was measured after curing the
samples under moist burlap for 7 days according to ASTM C
873. Flexural strength was also measured after this 7 day
curing period according to ASTM C 683. Shear bond tests
30 were used to measure the bonding of a new concrete mix to an
older existing subsurface. Concrete bases 2 inches high and
6 inches in diameter were made up to serve as existing sub-
; surfaces~ using 14.2 parts by weight Portland cement (Type I
non-air entraining according to ASTM C 150), 31.5 parts by
dry weight of sand conforming to ASTM C 33, 47.2 parts by
dry weight of grav~el and 7.1 parts total of water which were
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rnixed in the conventional manner. Concrete samples were
formed in cylindrical molds 4 inches high by 6 inches in
diameter by half-filling each mold with the above mixture.
These samples were aired in the molds for 7 days under moist
burlap and for a further 21 days in air to provide the
existing subsurface bases for shear bond testing. The top
surface of each of these samples was then sandblasted to re-
move about 0.175 inches from the surface in order to remove
fines and loose aggregate, and then washed with a garden
hose. While this surface was still wet, the remaining 2
inches of the mold were filled with the new cement mix to be
tested. The samples were then cured for 7 days under moist
burlap and in air for a further 21 days. The shear bond
strength of the interface between the existing concrete and
the new concrete was then measured according to the Arizona
shear bond test method outlined in the Federal Highway
Administration Report No. FHWA-RD-78-35 entitled "Styrene
Butadiene Latex Modifiers for Bridge Deck Overlay
Concrete". A comparison of the physical properties of the
samples is given in Table II. The data for compressive,
shear bond and flexural strength are averages from three
test specimens each.
Table II
SAMPLE
A B C
Compressive strength, psi39374280 4927
Shear bond strength, psi465 470 515
Flexural strength, psi 744 879 1121
Water:Cement Ratio0.54 0.35 0.33
Slump, inches 5 5 4
Air content, percent3.0 4.9 4.2
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It will be noted from Table II that the compressive
strength, shear bond strength and flexural strength were all
increased by the use of the latex and the dispersing agent,
(Sample B vs. Sample A) and increased even more with
additional dispersing agent (Sample C). Further, with
approximately the same amount of slump, the water:cement
ratio dropped from a normal 0.54 for the control Sample A to
the markedly lower values of 0.35 and 0.33 when both of the
additives were present. This lowering of the water:cement
ratio will provide by itself a more dense, higher strength
concrete.
Example 2
In this Example, additional samples of concrete mix
were prepared in accordance with the procedure followed as
described above in Example 1. In this case a comparison was
made to illustrate what varying amounts of the dispersing
agent accomplished for a constant amount of the latex add-
itive. This is illustrated by the preparation of Samples
D through I as shown in Table III. Materials used were the
~ same as those described in connection with Example 1.
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The physical properties of Samples D through I are given
in Table IV. Slump, air content and water:cement ratio were
obtained as described in connection with Example l. Com-
pressive strength data were obtained according to ASTM C 873
after curing to 7 days under moist burlap and/or after air
curing for a further 21 days. Shear bond strength data were
obtained as described in connection with Example 1 after
curing for 7 days under moist burlap and/or after air curing
for a further 21 days. Again compressive and shear bond
strength data are averages from three test specimens each.
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It will be noted from Table IV that at a constant amount
of the latex additive, the general trend is of increasing
compressive strength with increasing amounts of added dis-
persing agent. The amount of dispersing agent has little
effect on the shear bond strength.
EXAMPLE 3
Additional concrete samples were prepared as described in
connection with Example 1 to illustrate what the addition of
varying amounts of latex accomplished with approximately
equal amounts of added dispersing agent. Samples N through
Q were prepared as shown in Table V using the same materials
as described in connection with Example 1.
TABLE V
SAMPLE
N O P Q
Portland Cement 16.816.8 16.8 16.8
Limestone 31.631.6 31.7 31.7
Sand 43.543.5 43.6 43.6
20 Total water content 6.0 5.5 5.9 5.2
Latex 2.042.55 2.042.55
Dispersing Agent 0.025 0.032 0.081 0.10
Physical properties of these samples were determined as
described in connection with Examples 1 and 2 and are listed
in Table VI.
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TA~LE VI
SAMPLE
N O P Q
Compressive Strength after 28
days, psi 5483 5196 5626 5410
Shear bond strength after 28
days, psi 435 421 --- 443
Flexural strength after 28
days, psi 1041 973 --- 1040
lO Water:cement ratio 0.36 0.33 0.35 0.31
Slump, inches 4.05.0 5.0 4.0
Air content, percent 4.54.8 3.5 3.8
It will be noted from Table VI by comparing Samples N
and P (each containing 12 parts by dry weight of latex per
100 parts by weight of cement) with Samples O and ~ res-
pectively (each containing 15 parts of latex on the same
basis), that the compresssive strength decreases.
EXAMPLE 4
Additional samples were prepared to illustrate the
20 effect upon the concrete properties of changing the monomer
composition of the latex. Samples R and S use the latex of
example 1 and contain styrene, butadiene, acrylonitrile and
N-methyolacrylamide in the ratio of 66:34:2:2.5. Samples T
and U use a latex without the acrylonitrile monomer with a
ratio of styrene, butadiene and N-methyolacrylamide of
66:34:2.5. All other physical properties of the latexes are
the same. All samples were made up as described in connect-
ion with Example 1. Lomar D was again used as the dis-
persing agent and each Sample contained 15 parts by dry -
30 weight latex per 100 parts cement. Data are given in Table
VII.
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TABLE VI I
SAMPLE
R S T U
Weight percent
dispersing agent
based on dry weight
of latex 1.25 4.0 1.25 4~0
lO Compressive strength
after 7 days, psi 3963 4747 4460 5127
Water:cement ratio 0.36 0.31 0.37 0.36
Slump, inches 5.5 5.5 5.0 5.75
Air content, percent 5.6 3.0 3.5 3.5
Increasing the amount of dispersing agent again in-
creases the compressive strength of the concrete using both
the latex containing all four monomers (Samples R and S) and
the latex containing no acrylonitrile (Samples T and U).
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