Note: Descriptions are shown in the official language in which they were submitted.
132~311
sackground of the Invention
The present invention is directed to a novel
copolymer which can be utilized as a cement admixture to
greatly increase the fluidity or slump characteristics of
hydraulic cement compositions without causing excessive
retardation or prevent set of the treated composition.
Hydraulic cement compositions are brought into a
workable form by mixing the solid components with an
amount of water which is greater than that required to
hydrate the cement components therein. The mixed mineral
binder composition is poured into a form and allowed to
harden at atmospheric temperature. During the hardening,
some of 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 the resultant structure generally
bears an inverse relationship to the water-cement ratio of
the starting mix. The desire to use smaller quantities of
water is limited by the required flow and workability
properties of the fresh mixture. - -
It is desired in many applications to use unset -
cement compositions which are of low viscosity or even - - :
self-leveling and, at the same time, are capable of ~ -
forming a set cement of high compressive strength (via low
water-cement ratio). In structural cement compositions,
for example, it is highly desirable to maintain very low
water content in order to achieve high strength in the
final product. On the other hand, it is desirable that
the unset composition have fluid properties to enhance
mixing to cause uniform distribution of the liquid (water)
in the solid components, pumpability to permit the unset
cement composition to be carried to the needed structural
site and flowability to permit the unset cement
composition to be readily shaped into the desired form.
-: ' ' .
' ' "..
132~i311
Cement admixtures (The term "admixture" as used
herein and in the appended claims is a term of art
referring to compounds and compositions added to cement
mixtures or compositions to alter their properties. The
term does not imply that the components of an admixture do
or do not interact to cause the desired result.) capable
of causing the above-described viscosity reducing
characteristics are known. These materials are generally
categorized as ~water-reducing agents" if they are capable
of modifying viscosity to a limited degree or as "high
range water-reducing agents" or "superplasticizers" if
they have the ability to permit large water cuts in the
cement mixture while maintaining fluidity or cause large
increases in fluidity at constant water content. Lignin
sulfonates and polysaccharides are known water reducing
agents while sulfite-modified condensation products of
melamine-formaldehyde or sulfonate-modified condensation
products of naphthalene-formaldehyde are commercially
available superplasticizers. While these admixtures have
the advantage of increasing initial fluidity, they also ~ -
have the disadvantage of increasing the rate at which the
cement composition loses its fluidity or slump. H. P.
Preiss and H. R. Sasse, in Superplasticizers in Concrete,
Vol. II, Ed. by V. M. Malhotra et al, pages 733-750,
compare the effects of various known water-reducing agents
and superplasticizers including sulfonated
melamine-formaldehyde condensates, sulfonated
naphthalene-formaldehyde condensates, lignin-sulfonates
and polystyrene sulfonates. The study concludes that very
high dosages of any of the studied admixtures are needed
to appreciably increase the flow of cement compositions,
yet such dosages enhance the rate of slump loss and tend
to retard or prevent set.
In addition to the above mentioned known polymeric -~
materials, various polyacrylates have been considered as
' ' '.' ' ' ' '~ . ' ' ' . ', ~ ' " ' . " . ., . ' :, ' `' .. ' '', ' ' " ' ' : " .,, '
~ 3
cement superplasticizer admixtures. Polyacrylates of high
molecular weight have been found to be unsuitable as a
superplasticizer as they cause flocculation of cement
slurries. More recently, certain acrylic
acid-hydroxyalkyl acrylate copolymers have been suggested
as a flow enhancing agent. These copolymers are required
to be of low molecular weight and have a high acrylic acid
content to impart water solubility to the polymeric
composition and to have the copolymer exhibit stability in
a cementitious environment. Although these copolymers do
plasticize cement compositions, they impart excessive set
retardation to the composition so that they are not - -
suitable for general application.
It is highly desired to have superplasticizer
admixture compositions which can impart a high degree of
fluidity to cement compositions and can achieve this
result without adverse effect of set retardation.
Summary of the Invention
The present invention is directed to a novel
polymeric material and to cement admixtures composed of
said polymeric material. The admixture is capable of
providing a high degree of fluidity to cement compositions
without causing substantial set retardation.
The polymeric material i8 a copolymer comprising a water
601uble copolymer compoed of from 20 to 40 mole percent of an
ethylenically unsaturated acid 6elected from acrylic acid,
methacrylic acid or the alkali or alkaline earth metal salt
thereof and from 60 to 80 ~ole percent of a hydroxy C2-C3 alkyl
ester o~ an ethylenically unsaturated acid; selected from
acrylic acid and methacrylic acid; said copolymer having a
weight average molecular weight of at least 70,000.
Detailed Description of the Invention
It has been presently found that an unexpectedly high
degree of fluidity and extended work time of unset cement
... . .
-` 132~311
compositions can be achieved by having the compositions
contain small dosages of the cement superplasticizer
admixture of the present invention.
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 portland cement, water, sand
and aggregate, as is applicable for the particular
material being formed.
The cement compositions in which the present
admixture has been found useful include cement pastes,
that is, mixtures composed of a portland cement and water;
mortars composed of portland cement, water and sand in
standard amounts; and concrete compositions composed of
portland cement, water, sand, and aggregate, each in
standard amounts and size. The present invention is
particularly useful in concretes used to form structural
units. In each of the above-described cement
compositions, it is desirable to have low water to cement
ratios, such as from 0.2 to 0.6, preferably from 0.3 to
0.45, in order to form a set composition of suitable
strength. The amount of water present is inversely
proportional to the strength of the set cement composition
and, therefore, lowering the ratio is desirable.
The term "cement composition" as used in the present
disclosure and appended claims refers to pastes, mortars
and concrete compositions, as described above formed with
a portland or high silicate content cement. These cements
are conventionally known and are manufactured by calcining
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 aluminoferrite.
` ~ :
---`` 132~311
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 while 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 than normally attainable for
the same amount of cement. One further gains an extended
workability time without substantially extending the set
time of the resultant cement composition.
"Fluidity," nslump" and "workability" are
interrelated terms. Slump is term of art relating to a
standard test for determining the ease of movement of an
unset cement composition. The slump test measures the
amount of settlement of flow a shaped cement charge has ~ -
once under unsupported conditions. A cement composition
is workable, i.e. moldable, shapable, etc. while the
cement exhibits some degree of slump or flow
characteristics.
The subject polymer is a copolymer of (a) acrylic
acid or methacrylic acid and (b) a hydroxy(C2-C3)alkyl
ester of acrylic acid or methacrylic acid and can be
represented by the structural formula
-ECH2--~ ~CH2 ~3
COOz a : --
wherein each R separately represents a hydrogen or methyl -
group; Z represents a hydrogen atom or an alkali or
132531~
alkaline earth metal or mixtures thereof; ~1 represents
a hydroxy(C2-C3)alkyl group as, for example, 2-hydroxyethyl,
l-methyl-2-hydroxyethyl, 2-hydroxypropyl or 3-hydroxypropyl
and the like; x and y are integers such that the ratio of
x to y is 2:8 to 4:6 and the sum of x and y represent a high
molecular polymer having a weight average molecular weight
of at least 70,000 and preferably from 70,000 to 400,000 and
more preferably 90,000 to 400,000. The most preferred material
would be substantially free of low molecular weight material,
that is material having weight average molecular weights of
up to about 50,000. --
The copolymers described herein may be formed by
solution polymerization utilizing conventional free radical
initiators. The solvent must be a solvent for each of the
monomeric reactants but need not be a solvent for the
resultant copolymer. Examples of suitable solvents include
cyclic ethers such as tetrahydrofuran, dioxane and the like;
amides such as N,N-dimethylformamide and the like as well
as other organic liquids which are capable of solvating both -
the monomers and the resultant polymers. Water can also be
used as a polymerization medium. Other conventional
polymerization techniques, such as bulk polymerization, may
be used to produce the subject polymer.
The total monomer concentration should be between 10
and 40 (preferably from 25-40) weight percent based on the -~
total weight of the initial solution. The specific con-
centration depends on the solubility relationship of a
particular solvent, monomer and copolymer combination. The
polymerization reaction can be conducted at various tempera-
tures of from ambient to about the boiling temperature of
the solutions. Lower temperatures may be used, temperatures -
of from 40 - 80C being preferred. The reaction can be run
under atmospheric pressure although sub or superatmospheric
pressure may be used. The most preferred polvmerization~ -;
conditions are the use of a 30 weight percent monomer in
,D
. . .. .. . .... . . .. .. ........ , . . ~.. ~.. . . .. . .... . ...... .. .
132~311
dioxane run at 60C. --~
The polymerization is initiated using small amounts
of (e.g. 0.1 to 1.5 mole percent) a conventional free
radical polymerization initiator such as
azobisisobutyronitrile or the like. In addition, other
conventional free radical polymerization components such
.,
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7a
132~31~
as chain transfer agents (butanethiol, etc and the like
can be used to control molecular weight of the polymer.
The specific amounts required can be readily determined by
conventional methods.
The resultant polymer solution can be treated with a
material capable of precipitating the polymer from
solution. This material is, preferably, also a solvent
for residual monomer. Examples include non-cyclic ethers,
such as diethyl ether, chlorinated hydrocarbon, such as
chloroform and the like. The precipitated polymer can be
taken up in aqueous solution by neutralization with an
alkali or alkaline earth metal hydroxide, preferably
sodium hydroxide, to form the water soluble copolymer
product of the present invention.
The copolymer of the present invention is required to be
a high molecular weight material having a weight average
molecular weight of at least 70,000. Polymers of molecular
weights of from 70,000 to 400,000 are preferred and from
90,000 to 400,000 are most preferred. It has been unexpectedly
found that copolymers having a low concentration of acrylic
or methacrylic acid units of from 20 to 40 mole percent and the
above described molecular weight are water soluble and impart
the desired properties to cement compositions.
The above described copolymer has been unexpectedly
found to be a cement admixture which greatly enhances the
fluidity of a cement composition in relation to the same
cement composition which is void of the present admixture.
The admixture is normally an aqueous solution of the
alkali or alkaline earth metal salt form of the subject
copolymer. The polymer can be diluted with water to the
desired concentration to provide an admixture which can be
readily added to the cement composition. ~
The amount of the present superplasticizer cement -
admixture required in a cement composition should be an
effective amount to substantially reduce the water content
(by about 10 percent or greater) while retaining
equivalent slump of a blank cement composition or an
effective amount to substantially increase the slump
.,~ .
- 132~31 1
while maintaining the water to cement ratio, whichever is
desired. The specific amount of the present
superplasticizer cement admixture required to provide a
desired slump can be readily determined and will depend
upon the cement composition and the ratio of components of
the composition. Generally the amount will range from
about 0.01 to 2, preferably 0.1 to 0.5 weight percent of
total solids of the cement composition. Greater amounts
may be used but generally are unnecessary to achieve the
desired results.
The superplasticizer cement admixture of the present
invention can be added to cement compositions in any
conventional manner. For example, the components can be
added to the cement compositions substantially
simultaneously such as by previously mixing the
components, either in a dry state or as an aqueous
solution and adding the formed composition to the cement
composition. It is preferred that the present
superplasticizer be introduced into a cement composition
i as aqueous solution either simultaneously with, as part of
or subsequent to the addition of water used to form the
wet cement compositions such as just prior to utilization -~
of the cement composition. The subject superplasticizer --
cement admixture should be substantially uniformly mixed
with the cement composition to permit interaction between
the present admixture and the hydraulic cement of the
cement composition as well as interaction of the admixture
components (the exact nature of the interaction is unknown
and not meant to be a limitation on the present invention)
causing unexpected increased initial fluidity and
retention of fluidity over time.
The cement composition may contain other conventional
cement admixtures added in amounts and in manners known in
the art. For example, the cement composition containing
the superplasticizer described herein may also contain air
entraining agents such as resin soaps, alkyl benzene
----` 132~31~
sulfonates and the like or retarders such as gluconates,
sugars and the like as well as other admixtures.
The resultant cement structure, although formed from
a wet cement composition exhibiting great fluidity and
extended time of fluidity, is a structure of increased
strength. This is especially important and desirable when
the cement structure is a structural concrete formation.
The following examples are given for illustrative
purposes only and are not meant to be a limitation on the
subject invention except as defined in the claims appended
hereto. A11 parts and percentages are by weight unless
otherwise indicated.
Example I
A. Copolymerization was conducted at 28.7 weight percent
total monomer concentration in dioxane. The monomer
distribution was 40 mole percent acrylic acid and 60 mole
percent hydroxypropyl methacrylate (97% 2-hydroxypropyl).
The monomer-dioxane solution was introduced into a 3 neck
round bottom flask equipped with a magnetic stirrer,
thermometer, nitrogen gas inlet needle and a water-cooled
condenser for nitrogen egress. The reaction vessel was - -
purged with nitrogen gas for 30 minutes. 0.65 mole
percent azoisobutyronitrile (AIBN) was then introduced and
the reaction vessel was immersed into a glycerol bath
maintained at 56C. Polymerization was allowed to
continue for 5.5 hours after which the reaction vessel was
removed from the bath and allowed to cool. The polymer
product was precipitated with diethyl ether, filtered and
washed several times with fresh diethyl ether.
A sample of the unneutralized polymer was removed for
titration and gel permeation chromatography analysis. The
remaining polymer product was dried under vacuum at 80C
for 12 hours and was then taken up in distilled water
followed by neutralization with 5N NaOH to a
thymolphthalein end point. The neutralized product was ~
,', - ,
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.-
,,: , . . . ;, . , - - , .,- ,. ,-., - , . : , ~,, ~ .. . . . .
:` 132~3~
precipitated with tetrahydrofuran and then dried under
vacuum at 80C for 24 hours.
The molecular weight of the unneutralized product was
determined by gel permeation chromatography in
tetrahydrofuran on a a cross linked polystyrene size
exclusion column (~ Styragel of Waters Associates) using
polystyrene and polyethylene glycol ~tandards for
calibration. The ratio of monomeric units was determined
by gravimetric acid-base titration of the purified, free
acid copol~er.
The analysis of the copolymer product was as follows:
Acrylic acidlhydroxypropyl methacrylate ~mole %) 29/71
Sodium acrylate/hydroxypropyl methacrylate (wt ~) 21/79
Weight average molecular weight 341,000
B. The procedure described above was repeated except that
34 mole percent acrylic acid and 66 mole percent
hydroxypropyl methacrylate were added to the dioxane; 0.64
mole percent AIBN was added; and the bath reaction
temperature was 86C. An exotherm occurred raising the
reaction temperature to 93C. The polymerization was
allowed to run for 13.5 hours.
The copolymer product was analyzed as follows:
Acrylic acid/hydroxypropyl methacrylate ~mole %) 35/65
Sodium acrylate/hydroxypropyl methacrylate (wt %) 26/74
Weight average molecular weight 130,000
- .. ,; , . . ., , . ~. , , , , . ~
132~311
Example 2
Th~ copolymers prepared according to Example IA and
IB above were each added to cement pastes formed from Type
I cement mixed with water in a water to cement ratio of
0.45. Samples were prepared in which the copolymer was
added (at 0.4%-solid/total cement ~olid, s/8) as part of
the mix water ("Regular Addition") and additional samples
were prepared by first mixing the Type I cement with g5
percent of the total water and then an aqueous solution
composed of the remaining water and a copolymer sample was
added after a seven minute period ~Delayed Addition) to
each sample.
The flow properties were measured according to a
minislump flow test as described by L. M. Meyer and W. F.
Perenchio in Concrete International, Page 36-43 (Jan.
1979). The measurement was done after a period of eight -
minutes from the first addition of water. The set time of
each sample was analyzed by conventional calorimetry
determination on each of the regular addition samples. The
results are shown below:
Minisl ~P Flow (Diameter)
Polvmer Regular Addition Delayed Addition Set Time
(mm at 8 minutes)
A 155 123 11.25
B 155 197 il.7
Blank 88 88 8.0
~he above data shows that the copolymers A and B
both capable of imparting a high degree of fluidity to the ~
cement composition with both regular and delayed addition ~ ~-
and they imparted relatively little retardation.
Example 3 ~
The following example is given for comparative ~ -
purposes. Samples of low molecular weight copolymer rich
in acrylic acid were prepared and used as a cement -
composition fluidizer described in U.S. Patent 4,473,406
: ~ .
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~ r , -' ~ yr~
:
132~311
(hereafter labeled Polymer C). In addition, a similar
copolymer to that described in U.S. patent 4,473,406 was
prepared except it was a high molecular weight material
(hereafter labeled Polymer D). Finally, a polymer was
prepared for this comparison having the acrylic
acid/hydroxypropylmethacrylate (AA/HPMA) ratio substantially
the same as Sample IA except it was of low molecular we~ght
(hereafter Polymer E). Each of these materials was found to
be inferior to the copolymer of the present invention.
The copolymerization of each of the copolymers were
conducted in the same manner as the preparation of Example IA
described above. The specific conditions are given hereinbelow.
AA/HPMA
Monomer Product Product C4HgSH
Feed Free Acid Na SaltAIBN TemOp Time --
Polymer mole ~ mole % wt. % mole % mole % ~ hrs Mw
C 69/31 69/31 59/415.0 0.60 61 17.0 4,000
D 79/21 78/22 70/300 0.53 60 3.0 238,000
E 40/60 28/72 20/805.1 0.6S 59 5.5 7,700
Each of the copolymer products were used as a
fluidizer in a cement composition in the same manner as
described in Example 2 above. The results are given in
the Table below and directly compared with the results
shown in Example 2.
13
:,,
D
1325311 -
Minislump Flow Set Time
Polymer Regular Addition Delayed Addition
mm at 8 minutes (hrs)
A 155 123 11.25
B 152 197 11.7
C 102 146 19 . 0
D 40 192 15.75 .
E 10~1 111 1'.0
~lank 88 88 8.0
It is clearly shown that the copolymers of the
present invention ( A and B ) are unexpectedly capable
of imparting a high degree of fluidity to cement compositions
while maintaining reasonable set times. In contrast samples :
C ~ D exhibit a high degree of retardation. In addition, the : .
high molecular weight sample D exhibits stiffening due to . :
flocculation (shown by low flow value). Examples D and E ~ .
although showing a little retardation, exhibit a very low
degree of fluidification in both regular and delayed addition
performance. , :
.
' :
,~ :
~ ' ... .
' :':,:' ; :-:
''~ ' '' :~:
. D ; : :~
:: 14 ~- ~
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` 132~311
SU~,~C~
Removal of low molecular weight material can be
done by conventional msans such as dialysis,
ultrafiltration or the like methods.
5Example 4
B1. The procedure described in Example 1 was
repeated with 40 ~oles percent acrylic acid and 60 mole
percent HFMA added to dioxane; 0.65 mole percent AIBN was
added; and the bath reaction temperature was 80-C. The
10exotherm occurred raising the reaction temperature to 88-C.
The polymerization was allowed to run for 2.5 hours.
The copolymer product was analyzed as follows:
Acrylic acid/hydroxypropyl methacrylate (mole %) 39/61
Sodium acrylate/hydroxypropyl methacrylate (wt %) 29/71
15Weight average molecular weight 91,000 .
Example 5 ~ ~
The procedure described in Example 2 above was .
repeated with the copolymer prepared according to Example : ~:
4Bl above. The results are shown below:
20Minislump Flow (Diameter)
Polyme~ Regular A~dition Delayed Addition Set Time
(mm at 8 minutes)
4B1 132 179
.
The above data shows that the copolymer 4Bl is
25capable of imparting a high degree of fluidity to the
cement composition with both regular and delayed addition -~
and it impart-d relatively little retardation.
-, .
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.. :- -
. . .
~D ~ :
132~311
Example 6
The procedure describecl in Example 3 above was
repeated with a polymer which was prepared for comparative
purposes having an AA/HPMA ratio of 35/65 which was
substantially the same as Sample l-B and 4-Bl except for its
molecular weight (hereinafter Polymer F).
AA~MA
Monomer Product Product C4H9SH
Feed Free Acid Na SaltAIBN Temp T~me --
lO Polymer mole % mole % wt. % mole % mole % C hrs Mw
F 34/66 35/65 26/740.9 0.57 60 15.0 38,400
Copolymers 4B1 and F were used as a fluidizer in
a cement composition in the same manner as described in
Example 2 above. The results are given in the Table below
15 and directly compared with the results shown in Examples 2
and 5.
Ninislump Flow (Diameter)
PolYmer Regular Addition Delayed Addition Set Time
(mm at 8 minutes) (hrs)
Bl 132 179 ---
F 92 129 12.0
It is clearly shown that the copolymer of the
present invention (B1) is unexpectedly capable of imparting
a high degree of fluidity to cement compositions while
maintaining reasonable set times. Example F, although
showing a little retardation, exhibits a very low degree of
fluidification in both regular and delayed addition
performance.
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