ADMIXTURES AND METHOD FOR ACCELERATING THE SETTING OF PORTLAND CEMENT COMPOSITIONS

MELANGES ET METHODE POUR ACCELERER LE DURCISSEMENT DES COMPOSITIONS DE CIMENT PORTLAND

English Abstract

ABSTRACT OF THE DISCLOSURE

A method of and compositions for accelerating the setting
time of portland cement compositions are disclosed. Hydroxyacetic
acid and its sodium, potassium, calcium, lithium, zinc, and tri-
ethanolamine salts; lactic acid and its sodium, potassium, and
calcium salts, sodium dl-mandelate; and sodium 2-methyllactate in
particular ranges of concentrations relative to the cement are em-
ployed as accelerators for certain applications. The concentration
of admixture relative to cement necessary to achieve acceleration
depends upon the identity of the admixture, the water-cement ratio,
and the amount and type of aggregate in the composition, among other
factors. The accelerators are especially useful in shotcrete
applications.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:

1. A process of accelerating the setting time of a
quantity of portland cement composition for a particular water-
cement ratio, comprising the steps of:
(a) providing, as a chemical admixture, an .alpha.-hydroxy
carbonyl compound selected from the group consisting
of hydroxyacetic acid and its sodium, potassium
lithium, zinc and triethanolamine salts; sodium 2-
methyllactate; sodium dl-mandelate; and mixtures
thereof; and
(b) admixing with said cement composition an amount
of said .alpha.-hydroxy carbonyl compound sufficient to
accelerate the setting time of the portland cement
composition, at such water-cement ratio, as compared
with its setting time in the absence of any admixture.

2. The process according to claim 1 in which said
chemical admixture, and portland cement are essentially the only
constituents of the composition affecting its setting time.

3. The process according to claim 1 in which said
chemical admixture, portland cement, and water are essentially
the only constituents of the composition affecting its setting
time.

4. The process according to claim 3 in which the
.alpha.-hydroxy carbonyl compound is sodium hydroxyacetate.

5. The process according to claim 4 in which the
concentration of the sodium hydroxyacetate relative to the
cement is in a range whereby the final setting time of the
composition as measured by the Vicat Needle test is less than
one hour.

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6. The process according to claim 5 in which the
portland cement composition includes a quantity of water to
constitute a cement paste and the concentration of the sodium
hydroxyacetate relative to the cement is in the range of from
about 0.5 to about 10 weight percent.

7. The process according to claim 5 in which the
portland cement composition includes quantities of water and
aggregate to constitute a mortar or a concrete and the concen-
tration of the sodium hydroxyacetate relative to the cement
is in the range of from about 1.1 to about 10 weight percent.

8. A process of accelerating the setting time of a
quantity of portland cement composition for a particular water-
cement ratio, comprising the steps of:
(a) providing, as a chemical admixture, an .alpha.-hydroxy
carbonyl compound selected from the group consisting
of hydroxyacetic acid and its sodium, potassium, lithium,
zinc and triethanolamine salts; lactic acid and its
sodium, potassium and calcium salts; sodium 2-methyl-
lactate; sodium dl-mandelate; and mixtures thereof;
and
(b) admixing with said cement composition an amount
of said .alpha.-hydroxy carbonyl compound sufficient to
accelerate the setting time of the portland cement
composition, at such water-cement ratio, as compared
with its setting time in the absence of any admixture;
wherein said chemical admixture, portland cement, and water are
essentially the only constituents of the composition affecting
its setting time.

9. The process according to claim 8 in which the
.alpha.-hydroxy carbonyl compound is sodium lactate.

19

10. The process according to claim 8 in which the
concentration of the .alpha.-hydroxy carbonyl compound relative to
the cement is in a range whereby the final setting time of the
composition as measured by the Vicat Needle test is less than one
hour.
11. A process of preparing a quantity of portland
cement composition for shotcreting, comprising the steps of:
(a) providing, as a chemical admixture, an .alpha.-
hydroxy carbonyl compound selected from the group con-
sistingof hydroxyacetic acid and its sodium, potassium,
calcium, lithium, zinc, and triethanolamine salts;
sodium 2-methyllactate; sodium dl-mandelate; and mix-
tures thereof;
(b) mixing portland cement, aggregate, and water to
form a quantity of shotcrete having a particular
water-cement ratio; and
(c) admixing with the portland cement, aggregate, and
water an amount of said .alpha.-hydroxy carbonyl compound
sufficient to accelerate the final setting time as mea-
sured by the Proctor Needle test, at such water-cement
ratio, to a value of less than fifteen minutes, the
setting time of the shotcrete thereby being accelerated
as compared with its setting time in the absence of any
admixture.

12. The process according to claim 11 in which said
chemical admixture, aggregate, water, and portland cement are es-
sentially the only constituents of the composition affecting its
setting time.






13. The process according to claim 12 in which the
.alpha.-hydroxy carbonyl compound is calcium hydroxyacetate.

14. The process according to claim 12 in which the
concentration of the .alpha.-hydroxy carbonyl compound relative to the
cement is in the range of from about 1.1 to about 10 weight
percent.

15. A process of preparing a quantity of portland
cement composition for shotcreting, comprising the steps of:
(a) providing, as a chemical admixture, an .alpha.-hydroxy
carbonyl compound selected from the group consisting of
hydroxyacetic acid and its sodium, potassium, lithium,
zinc, and triethanolamine salts; sodium 2-methyllactate;
sodium dl-mandelate; and mixtures thereof;
(b) mixing portland cement, aggregate, and water to
form a quantity of shotcrete having a particular water-
cement ratio; and
(c) admixing with the portland cement, aggregate,
and water an amount of said .alpha.-hydroxy carbonyl compound
sufficient to accelerate the final setting time as
measured by the proctor Needle test, at such water-
cement ratio, to a value of less than fifteen minutes,
the setting time of the shotcrete thereby being acceler-
ated as compared with its setting time in the absence of
any admixture.

16. The process according to claim 15 in which said
chemical admixture, aggregate, water, and portland cement are
essentially the only constituents of the composition affecting
its setting time.




21


17. The process according to claim 16 in which the
concentration of the .alpha.-hydroxy carbonyl compound relative to the
cement is in the range of from about 1.1 to about 10 weight
percent.

18. A process of preparing a quantity of portland
cement composition for shotcreting, comprising the steps of:
(a) providing, as a chemical admixture, an a-
hydroxy carbonyl compound selected from the group con-
sisting of hydroxyacetic acid and its sodium, potassium,
calcium, lithium, zinc, and triethanolamine salts; lac-
tic acid and its sodium, potassium, and calcium salts;
sodium 2-methyllactate; sodium dl-mandelate; and mix-
tures thereof;
(b) mixing portland cement, aggregate, and water
to form a quantity of shotcrete having a particular
water-cement ratio; and
(c) admixing with the portland cement, aggregate, and
water an amount of said .alpha.-hydroxy carbonyl compound
sufficient to accelerate the final setting time as meas-
ured by the Proctor Needle test, at such water-cement
ratio, to a value of less than fifteen minutes, the
setting time of the shotcrete thereby being accelerated
as compared with its setting time in the absence of
any admixture;
wherein said chemical admixture, aggregate, water, and portland
cement are essentially the only constituents of the composition
affecting its setting time.

19. The process according to claim 18 in which the
concentration of the .alpha.-hydroxy carbonyl compound relative to the
cement is in the range of from about 1.1 to about 10 weight per-
cent.

22


20. A portland cement concrete patching compound mixable
with water to a selected water-cement ratio and comprising
portland cement, aggregate, and, as a chemcial admixture, an
.alpha.-hydroxy carbonyl compound selected from the group consisting of
hydroxyacetic acid and its sodium, potassium, lithium, zinc, and
triethanolamine salts; sodium 2-methyllactate; sodium dl-mandelate;
and mixtures thereof; the concentration of the .alpha.-hydroxy carbonyl
compound relative to the cement being sufficient to accelerate
the final setting time, as measured by the Vicat Needle test at
such water-cement ratio, to a value of less than one hour, the
setting time of the concrete patching compound thereby being
accelerated as compared with its setting time in the absence of
any admixture.

21. The portland cement concrete patching compound
according to claim 20 in which said chemical admixture, aggregate,
and portland cement are essentially the only constituents of the
composition affecting its setting time.

22. A portland cement quick-setting-mortar compound
mixable with water to a selected water-cement ratio and comprising
portland cement, aggregate, and, as a chemical admixture, an .alpha.-
hydroxy carbonyl compound selected from the group consisting of
hydroxyacetic acid and its sodium, potassium, calcium, lithium,
zinc, and triethanolamine salts; sodium 2-methyllactate; sodium
dl-mandelate; and mixtures thereof; the concentration of the
.alpha.-hydroxy carbonyl compound relative to the cement being
sufficient to accelerate the final setting time, as measured by
the Vicat Needle test, at such water-cement ratio, to a value of
less than thirty minutes, the setting time of the quick-setting-
mortar compound thereby being accelerated as compared with its
setting time in the absence of any admixture.

23

23. The portland cement quick-setting-mortar compound
according to claim 22 in which said chemical admixture, aggregate,
and portland cement are essentially the only constituents of the
composition affecting its setting time.

24. A portland cement plugging compound mixable with
water to a selected water-cement ratio and comprising portland
cement, aggregate, and, as a chemical admixture, and .alpha.-hydroxy
carbonyl compound selected from the group consisting of hydroxy-
acetic acid and its sodium, potassium, calcium, lithium, zinc,
and triethanolamine salts; sodium 2-methyllactate; sodium dl-
madelate; and mixtures thereof; the concentration of the .alpha.-hydroxy
carbonyl compound relative to the cement being sufficient to
accelerate the final setting time, as measured by the Vicat Needle
test, at such water-cement ratio, to a value of less than fifteen
minutes, the setting time of the plugging compound thereby being
accelerated as compared with its setting time in the absence of
any admixture.

25. The portland cement plugging compound according to
claim 24 in which said chemical admixture, aggregate, and port-
land cement are essentially the only constituents of the com-
position affecting its setting time.

26. A portland cement concrete patching compound mixable
with water to a selected water-cement ratio and consisting
of portland cement, aggregate, and, as a chemical admixture,
an .alpha.-hydroxy carbonyl compound selected from the group consisting
of hydroxyacetic acid and its sodium, potassium, lithium, zinc,
and triethanolamine salts; lactic acid and its sodium, potassium,
and calcium salts; sodium 2-methyllactate; sodium dl-mandelate;
and mixtures thereof; the concentration of the a-hydroxy
carbonyl compound relative to the cement being sufficient to accel-



24


erate the final setting time, as measured by the Vicat Needle
test at such water-cement ratio, to a value of less than one
hour, the setting time of the concrete patching compound thereby
being accelerated as compared with its setting time in the absence
of any admixture.

27. A portland cement quick-setting-mortar compound
mixable with water to a selected water-cement ratio and consis-
ting of portland cement, aggregate, and, as a chemical admixture,
an .alpha.-hydroxy carbonyl compound selected from the group consisting
of hydroxyacetic acid and its sodium, potassium, calcium, lithium,
zinc, and triethanolamine salts; lactic acid and its sodium,
potassium, and calcium salts; sodium 2-methyllactate; sodium
dl-mandelate; and mixtures thereof; the concentration of the
.alpha.-hydroxy carbonyl compound relative to the cement being
sufficient to accelerate the final setting time, as measured by
the Vicat Needle test, at such water-cement ratio, to a value of
less than thirty minutes, the setting time of the quick-setting-
mortar compound thereby being accelerated as compared with its
setting time in the absence of any admixture.

28. A portland cement plugging compound mixable with
water to a selected water-cement ratio and consisting of portland
cement, aggregate, and, as a chemical admixture, an .alpha.-hydroxy
carbonyl compound selected from the group consisting of hydroxy-
acetic acid and its sodium, potassium, calcium, lithium, zinc,
and triethanomlaine salts; lactic acid and its sodium, potassium,
and calcium salts; sodium 2-methyllactate; sodium dl-mandelate;
and mixtures thereof; the concentration of the .alpha.-hydroxy carbonyl
compound relative to the cement being sufficient to accelerate the
final setting time, as measured by the Vicat Needle test, at
such water-cement ratio, to a value of less than fifteen minutes,
the setting time of the plugging compound thereby being






accelerated as compared with its setting time in the absence
of any admixture.

29. The portland cement concrete patching compound
according to claim 20 in which the concentration of the .alpha.-hydroxy
carbonyl compound relative to the cement is in the range of
from about 1.1 to about 10 weight percent.

30. The portland cement quick-setting-mortar compound
according to claim 22 in which the concentration of the .alpha.-hydroxy
carbonyl compound relative to the cement is in the range of from
about 1.1 to about 10 weight percent.
31. The portland cement plugging compound according to
claim 24 in which the concentration of the .alpha.-hydroxy carbonyl
compound relative to the cement is in the range of from about 1.1
to about 10 weight percent.

32. The portland cement concrete patching compound
according to claim 26 in which the concentration of the .alpha.-hydroxy
carbonyl compound relative to the cement is in the range of from
about 1.1 to about 10 weight percent.

33. The portland cement quick-setting-mortar compound
according to claim 27 in which the concentration of the .alpha.-hydroxy
carbonyl compound relative to the cement is in the range of from
about 1.1 to about 10 weight percent.

34. The portland cement plugging compound according to
claim 28 in which the concentration of the .alpha.-hydroxy carbonyl
compound relative to the cement is in the range of from about 1.1
to about 10 weight percent.




26


35. A portland cement concrete patching compound mixable
with water to a selected water-cement ratio and consisting
essentially of portland cement, aggregate, and, as a chemical
admixture, an .alpha.-hydroxy carbonyl compound selected from the group
consisting of hydroxyacetic acid and its sodium, potassium,
lithium, zinc and triethanolamine salts; lactic acid and its
sodium, potassium, and calcium salts; sodium 2-methyllactate;
sodium dl-mandelate; and mixtures thereof; the concentration of
the .alpha.-hydroxy carbonyl compound relative to the cement being
sufficient to accelerate the final setting time, as measured by
the Vicat Needle test at such water-cement ratio, to a value of
less than one hour, the setting time of the concrete patching
compound thereby being accelerated as compared with its setting
time in the absence of any admixture, the portland cement and
the .alpha.-hydroxy carbonyl compound being the only constituents
of the concrete patching compound influencing its setting time.

36. A portland cement quick-setting-mortar compound
mixable with water to a selected water-cement ratio and consisting
essentially of portland cement, aggregate, and, as a chemical
admixture, an .alpha.-hydroxy carbonyl compound selected from the
group consisting of hydroxyacetic acid and its sodium, potassium,
calcium, lithium, zinc, and triethanolamine salts; lactic acid and
its sodium, potassium, and calcium salts; sodium 2-methyllactate;
sodium dl-mandelate; and mixtures thereof; the concentration of
the .alpha.-hydroxy carbonyl compound relative to the cement being
sufficient to accelerate the final setting time, as measured by
the Vicat Needle test, at such water-cement ratio, to a value of
less than thirty minutes, the setting time of the quick-setting-
mortar compound thereby being accelerated as compared with its
setting time in the absence of any admixture, the portland
cement and the .alpha.-hydroxy carbonyl compound being the only constitu-
ents of the quick-setting-mortar compound influencing its


27



setting time.

37. A portland cement plugging compound mixable with
water to a selected water-cement ratio and consisting essentially
of portland cement, aggregate, and, as a chemical admixture,
an .alpha.-hydroxy carbonyl compound selected from the group consisting
of hydroxyacetic acid and its sodium, potassium, calcium, lithium,
zinc, and triethanolamine salts; lactic acid and its sodium,
potassium, and calcium salts; sodium 2-methyllactate; sodium
dl-mandelate; and mixtures thereof; the concentration of the
.alpha.-hydroxy carbonyl compound relative to the cement being
sufficient to accelerate the final setting time, as measured by
the Vicat Needle test, at such water-cement ratio, to a value of
less than fifteen minutes, the setting time of the plugging
compound thereby being accelerated as compared with its setting
time in the absence of any admixture, the portland cement and the
.alpha.-hydroxy carbonyl compound being the only constituents of the
plugging compound influencing its setting time.


28

Description

)71Z~ -

B~CKGROUND OF THE-INVENTION
This invention relates to a method of accelerating the
setting time of concretes, mortars, and other compositions con-
taining portland cement (i.e. "portland cement compositions") and
to the use as accelerators of certain CL-hydroxy carbonyl compounds,
primarily hydroxyacetic (glycolic) acid, lactic acid, and certain
~alts of hydroxyacetic, lactic, 2-methyllactic, and dl-mandelic
acids, in concentrations relative to the cement within ranges as
specified herein.
Additives for modifying the setting time and other pro-
perties of portland cement compositions have been employed virtu-
ally since the beginning of cement technology in the 1870's. Cem-
ent itself, a mixture of (1~ lime-containing material such as
limestone, shell or chalk, and (2) clay or a source of clay such
as shale or slate, flash sets in a matter of seconds or minutes
when mixed with water, leaving virtually no time for adequate mix-
ing, pouring, or other necessary processing operations. To make
it commercially useful, therefore, essentially all cement as sold
contains a few percent gypsum, which delays setting for a number
of hours. In order to shorten or lengthen setting time for speci-
fic applications, accelerating or retarding admixtures are employed.
Such admixtures are defined by ASTM publication C 494-71, which
also defines "water reducing" admixtures as those which reduce the
amount of water necessary to produce concrete of a given consis-
tency, Both accelerating and retarding admixtures are known which
also effect water reduction.
The setting times for commercially available cements vary
fairly widely, but are typically on the order of three hours as
determined by the final setting time of the Vicat Needle method
(ASTM C 191). The setting times of mortars made with such cements
measured by the initial setting time of the Proctor Needle test

(ASTM C 403) is about seven hours. (As is widely recognized in
this art, both the Vicat Needle and Proctor Needle tests may be


-- 1 -- ~, i-

71Z'~'~
used to determine setting times of various portland cement compo-
sitions of Yarious proportions, e.g. water-cement ratios, and are
not restricted to the specific compositions and proportions of in-
gredients recited in ASTM C 191 and ASTM C 403. As used herein,
the terms "Vicat Needle test" and "Proctor Needle test" refer to
carrying out generally the procedures specified in the ASTM refer-
ences on the particular sample of portland cement composition of
interest), These setting times must be significantly reduced, for
example, in the manufacture of molded concrete products such as
concrete blocks, in the manufacture of pavements and bridge sur-
faces, and in the construction of concrete buildings. In numerous
applications, the impetus for shortening the setting time is at
least in part the high cost of overtime labor.
One application which inherently demands very short set-
ting times is shotcreting, a process of spraying mortar on a sup-
porting surface to obtain both structural strength and desired
surface properties. Shotcreting is employed for example in the
construction of tunnels drilled through rock, and the concrete must
achieve a high percentage of its ultimate strength after it is
sprayed on in a shorter period than the relaxation time of the
rock in order to prevent the tunnel from collapsing.
There are both so-called wet and dry shotcrete processes.
In the wet process, the cement mixture including water is fully
prepared and then sprayed on the tunnel wall or other surface from
a nozzle. In the dry process, all the dry ingredients are mixed
and fed to the nozzle, and the water is added in the nozzle. Note
that greater acceleration of setting time can be achieved generally
with the dry process because there is no risk of the mixture setting
up in the equipment prior to being sprayed. In either process the
shotcrete must harden in less than fifteen minutes as measured by
the Proctor Needle test final setting time in order that a useful
thickness of shotcrete may be applied to a surface without its

sloughing off.


)'7~'~44

Accelerating admixtures for shotcreting in general com-
mercial use today are mixtures of sodium carbonate~and sodium
aluminate. While they afford acceptable early strengths relative
to plain mortar, they typically reduce the ultimate strength of
the mortar by more than half, requiring the use of thicker layers
of mortar than would be necessary in the absense of the accelerator
to achieve the same structural strength. Additionally, these ad-
mixtures are highly caustic and great care must be taken in handl-
ing them. Only a limited degree of acceleration can be achieved
with sodium carbonate-sodium aluminate accelerators without reduc-
ing the ultimate strength of the shotcrete to an unacceptable
level. There exist applications requiring shorter setting times
and rapid early strength development for which no satisfactory
accelerating admixtures have been available.
A second application which requires very fast setting
times is the use of portland cement plugging compounds. Plugging
compounds consist of portland cement, fine aggregate such as mas-
on's sand, and an accelerator and are used to repair broken or
cracked concrete when water is leaking through the fracture. Plug-

ging compounds must have a final setting time as measured by theVicat Needle test of less than fifteen minutes in order to ensure
that the compound will harden and stop the leak before it is
washed away.
Portland cement compositions used to repair damaged con-
crete articles and structures must harden quickly so that the time
taken to make the repair will be short. Quick-setting-mortar
compounds generally consist of portland cement, fine aggregate,
and an accelerator and are used for repairing chipped or cracked
concrete and other small jobs. They require final setting times of
thirty minutes or less as measured by the Vicat Needle method.
Concrete patching compounds contain cement, coarse and fine aggre-

gate, and an accelerator and are generally used for making larger
repairs such as filling potholes in concrete pavement. Concrete


071Z4~

patching compounds must have final setting times of one hour or
less as measured by the Vicat test, the setting times typically
being somewhat longer than the setting times of quick-setting-
mortar compounds because of the longer time required to mix and
apply the larger quantities of concrete patching compound. The
Vicat Needle test may be carried out directly on samples of mortar.
In the case of concrete, the Vicat test is carried out on the mor-
tar of the sample, which may be separated from the coarse aggregate
by sieving, as provided in ASTM C 403.
Perhaps the most widely used accelerator for most con-
crete applications is calcium chloride. Although it does not ac-
celerate setting times sufficiently for use in shotcrete processes,
it is used for most other applications and has the advantage of
being very inexpensive. It is severely limited however, in that
chloride ion is highly corrosive in contact with ferrous metals,
and also promotes an electrochemical reaction between dissimilar
metals. Hence calcium chloride generally cannot be used as an
accelerator for reinforced concrete or other applications involv-
ing concrete-metal interfaces.
It has been known since the late 1930's that certain
organic hydroxy carbonyl compounds could influence the setting times
of portland cement, but in a manner precisely opposite that con-
templated by this invention. The prior art teaches that certain
hydroxy carbonyl compounds, including som~ of the ~-hydroxy car-
bonyl compounds of the present invention, retard the setting of
portland cement rather than accelerate it. This prior art, the
most pertinent of which is discussed below, does not disclose or
suggest the accelerators of the present invention and in fact
teaches away from the present invention. In spite of the widely-
recognized drawbacks of the accelerators in use today, it has not
been recognized that the o~-hydroxy carbonyl compounds of the pres-

ent invention function as suitable accelerators for the applica-
tions disclosed even though certain of these compounds are
disclosed in the prior art as admixtures for portland cement.


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- 107~Z44
A review of the prior art relating to accelerators in
general and to hydroxy-carbonyl retarders demonstrates that it is
difficult to make generalizations about the effect of broad classes
of compounds on the setting times of portland cement. For example,
although the essentially ionic salt calcium chloride is an effi-
cient accelerator, sodium chloride and potassium chloride, also
ionic chlorides, are substantially less efficient accelerators.
Moreover merely because a particular compound functions as an acce-
lerator does not imply that there are concentrations at which it
will shorten setting times sufficiently to be used in applications
such as shotcrete and plugging compounds which require particula-
rily short setting times. As noted above, for example, calcium
chloride is a widely used accelerator for portland cement, but it
does not shorten setting times sufficiently to be used for shot-
creting.
One reference teaches broadly that theoL-hydroxy carbonyl

grOUP~ H
O O
7 , is very active in retarding the
hydration of portland cement, the degree of hydration being a
measure of its degree of hardening. In this reference; Proceedings
of the International Symposium on the Chemistry of Cement, Washing-
ton, 1960, pages 924-925; J. H. Taplin classifies hydroxyacetic
acid as a strong retarder on the basis of data obtained from cem-
ent paste specimens having water-cement ratios of 0.30 and contain-
ing one percent admixture by weight. Lactic acid, classified as
having a negligible retarding effect, is called exceptional in
that it contains the ~-hydroxy carbonyl group but does not retard.
This observation by Taplin indicates the difficulty of making broad
generalizations concerning the effects of classes of compounds on
the setting times of portland cement. Taplin nonetheless concludes

that "it appears to be a general rule, that for an organic sub-
stance to retard cement, it must have at least two oxygen atoms


-- 5 --

~071Z44

each bound to a single but different carbon atom in such a way
that the oxygen atoms can approach each other." The Taplin refer-
ence contains no teaching or sugges~ion that hydroxyacetic or lac-
tic acid might be useful as an accelerator for portland cement
compositions and plainly leads away from the present invention.
A second reference which similarly teaches away from the
present invention is U. S. Patent No. 3,144,347, issued August 11,
1964 to E. I. du Pont de Nemours & Company. The '347 patent teaches
the use of hydroxyacetic, lactic acid, and their sodium, calcium,
potassium and amine salts as retarding admixtures in concentrations
ranging from about 0.001 to 3.5 weight percent relative to the cem-
ent. The patent recites further (Column l, lines 33-35) that
"most often less than about 0.8 weight percent will be used, and
particularly advantageous results are obtained within the narrow
range of 0.01 to 0.1 weight percent", and all of the specific ex-
amples contained in columns 3 and 4 of the patent relate to the use
of less than 0.8 weight percent of the foregoing retardant admix-
tures in concretes. The second paragraph of the patent defines the
scope of the asserted invention as relating to "a small class of
monohydroxy organic compounds . . . which not only serve as excel-
lent water reducing retardants but at the same time causes a signi-
ficant increase in the compressive strength of the concrete." The
sole and plain teaching of the '347 patent is thus that the recited
compounds are useful as retarding agents and concomitantly as ulti-
mate strength increasing agents.
The only suggestion whatsoever in the prior art that a
specific ~-hydroxy carbonyl compound may have some utility as an
accelerator is found in Japanese Patent Application Publication
13680 of 1972, dated 24, April, 1972 and assigned to Hani Chemical
Company, Ltd., by Kenji Harazawa. Precisely what the Harazawa
patent does or does not teach one of ordinary skill in this art is

at best unclear. It states that calcium monglycolate and calcium
diglycolate effect a limited reduction in the initial setting time


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^` 1~71Z44

of portland cement, and further that "it is particularly preferred
to use portland cement and mixed gypsum plaster." I am not sure
what "gypsum plaster" is, or why one would want to mix it with
cement. Although the terminology is ambiguous, calcium diglycolate
is generally used to refer to the calcium salt of diglycolic acid,
which is not an ~-hydroxy carbonyl compound. Even giving Harazawa
the benefit of all doubts, his preferred range is between 0.05 and
0 15 percent admixture with respect to the cement, and the shortest
final setting time disclosed for either compound is one hour and
forty-five minutes and the shortest final setting time for calcium
monoglycolate is one hour and fifty minutes, as measured by JIS
R-5201, a Vicat Needle test. For reasons stated above, it is not
possible to extrapolate with respect to the effect of higher con-
centrations of admixture, and Harazawa contains no suggestion what-
soever that the salts recited by him, or any other compounds,
might make useful accelerators for applications requiring fast
setting times such as shotcreting, plugging compounds, and quick-
setting mortars. The patent contains no suggestion of the inven-
tion disclosed and claimed herein.
SUMMARY OF THE INVENTION
The present invention is based upon the discovery that
certain ~-hydroxy carbonyl compounds, when mixed with portland cem-
ent compositions in particular concentrations relative to the cem-
ent, may be used as accelerators for such compositions in broad
classes of applications. More particularly hydroxyacetic acid and
its sodium, potassium, calcium,lithium, zinc, and triethanolamine
salts; lactic acids and its sodium, potassium, and calcium salts;
sodium dl-mandelate; and sodium 2-methyllactate, when admixed in
concentrations of from about 0.5 to 10 weight percent relative to
the cement have been found to function as suitable accelerators for
many applications, although in some cases they may function as

retardants in lower and in higher concentrations.
The precise range of concentration of the admixture rela-
tive to the cement over which the admixture function as an accele-



1~71Z44

rator in accordance with the present invention will vary for spec-
ific applications depending upon the chemical identity of the
admixture, the water-cement ratio, the nature and quantity of
aggregates in the composition, the composition of the cement, the
order in which the ingredients of the composition aré mixed, and
the temperature and other conditions under which the composition
i~ mixed and set. For example, potassium hydroxyacetate was found
to accelerate the final setting time of cement pastes as measured
by the Vicat Needle test when present in concentrations greater
than about 0.5% by weight relative to the cement and to retard the
setting time in concentrations less than this value. In mortar
made from the same cement the salt functions as an accelerator as
determined by the Proctor Needle test initial setting time in con-
centrations greater than about 1.3% and as a retardant below this
value. Although the concentration range over which the admixtures
disclosed herein function as accelerators is between about 0.5 to
10 percent, the term "accelerating concentration" is used herein
in accordance with the teachings hereof to more precisely specify
the range within which each particular admixture acts as an accel-

erator, taking into account variations in the several factorsreferred to above.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be better appreciated if reference is
made to the following drawings:
Figure 1 is a plot of the initial setting time of mortars
as measured by the Proctor Needle method versus concentration of
potassium hydroxyacetate,
Figure 2 is a plot of compressive strength versus time
for a control cement and cement containing 3% potassium hydroxy-

acetate,

Figure 3 is a plot of percent water reduction in mortarversus concentration of potassium hydroxyacetate, and
Figure 4 is a plot of the final setting time of mor-


7~2g4

tars as measured by the Vicat Needle method versus concentration

of calcium hydroxyacetate.
EFFECT OF ADMIXTURES OF THE PRESENT
INVENTION ON SETTING TIMES
r
Figure 1 shows a plot of the initial setting time (inhours) of a mortar as a function of the concentration of potassium
hydroxyacetate in which the horizontal scale is logarithmic and in-
dicates the weight percent of admixture relative to the cement of
the mortar, Atlas Type I cement was employed and mixed with 21/2
parts by weight Federal Fine sand for each part of cement. The
water-cement ratio was 0.50 by weight and setting times were mea-
sured by the Proctor Needle method. A control sample containing
no admixture was found to have an initial setting time of 6.8 hours
and is represer,ted on the graph by the horizontal line. All points
above the line indicate that the admixture is functioning as a
retardant and at all points below the line the admixture is func-
tioning as an accelerator. The plot reveals that the potassium
hydroxyacetate functions as an accelerator at concentrations below
0.05 weight percent and above 1.3 weight percent. The foregoing
concentrations are therefore referred to herein as "crossover
points", useful in defining the range of concentration over which
each specific admixture functions as an accelerator. Note that be-
tween the 1.3% concentration crossover point and the next point on
the plot at about 1.6% concentration, the slope of the curve is
almost vertical and the setting time is reduced from 6.8 hours to
less than one half hour. At a concentration of 5.0% the setting
time is about five minutes.
Table 1 lists the crossover points from retardation to
acceleration for hydroxyacetic acid and some of its salts, as de-
termined from plots of initial setting time (Proctor Needle) versus
concentration similar to Figure 1. Admixtures of this table other

than potassium hydroxyacetate seem to exhibit a somewhat less steep
slope than that of Figure 1 about the crossover point. The admixtures


~712~

in concen*rations greater than the crossover point values cause
acceleration. The mortar samples tested are the same as those
employed with respect to the results shown in Figure l.

~ABL~' 1
Weight Percent of Salt
Admixtureat Crossover Concentration
Hydroxyacetic Acid1.1%
Lithium Hydroxyacetate 1.4%
Sodium Hydroxyacetate 1.25%
Potassium Hydroxyacetate 1.3
Calcium Hydroxyacetate 2.2~
Plots of setting times versus concentration for differ-
ent admixtures of the present invention do not resemble Figure 1
in every case, since the shape of the curves depends upon a number
of factors, such as the identity of the admixture, the water-cement
ratio, and the temperature of the mix, which influence the rate of
hardening of portland cement mixes generally. Thus not all accele-
rators within the scope of this invention function as retardants in
concentrations that are without the scope of the invention inso-
far as is presently known.
As may be seen in Figure 4, calcium hydroxyacetate, pre-
pared by neutralizing a 70-percent solution of hydroxyacetic acid
with calcium hydroxide, functions as an accelerator under certain
conditions over the entire concentration range from 0.05 to 6.0
weight percent as measured by the Vicat Needle test final setting
time. The mortar for these tests was made up of 2.5 pounds of
Federal Fine Sand per pound of Atlas Cement with a water-cement
ratio of 0 30. The final setting time for a control mix containing
no admixture was 3.5 hours. The curve exhibits a sharp break be-
tween 0.83 and 1.5 weight percent, but the admixture functions as
an accelerator on either side of the break. As is evident from the

figure, under these conditions calcium hydroxyacetate is suitable
for shotcreting, plugging compounds, quick-setting mortar compounds,
and other applications requiring very short settingti~es only in


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~7124~
concentrations in excess of about 1.5 weight percent relative to
; the cement~ Under the conditions employed to obtain the crossover
point for calcium hydroxyacetate listed in Table 1, the graph of
initial setting time, measured by the Proctor Needle method in this
case, versus concentration more nearly resembles Figure 1 than
; Figure 4 in that the setting time is retàrded over a portion of the
concentration range tested. A crossover therefore occurs between
retardation and acceleration.
The triethanolamine salt of hydroxyacetic acid functions
as an accelerator in cement paste with a water-cement ratio of 0.30
at concentrations as low as 0.5 percent and appears to function as
an accelerator at all higher concentrations, at least up to about
10~. Similarly, the sodium salt of dl-mandelic acid does not app-
ear to function as a retardant.
Note that hydroxyacetic acid, lactic acid, 2-methyllactic
acid, and dl-mandelic acid are structurally similar in that they
all have one hydroxy group and one carboxylic acid group, and in
particular the hydroxy group is located in the "~" position rela-
tive to the carbonyl carbon atom.
Generally, admixtures of the present invention are more
effective as accelerators if they are added to the other ingredients
of the cement composition before water is added to the mix. For
example, a higher concentration of admixture is required to achieve
a given degree of acceleration if moist or wet sand has been mixed
with the cement before the accelerator is added.
The chemical reactions which lead to the hardening of
cement are not well understood. Many researchers believe that gyp-
sum acts to retard the setting time of cement by supplying sulfate
ions to react with tricalcium aluminate present in the cement.
The sulfate ions react with the surface of the tricalcium aluminate
particles, producing a compound called ettringite which coats the
outer surface of the particle. Lime also is believed to precipi-

tate on the particles. The relatively impervious coating of



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`` 107~L244

ettringite and lime prevents the tricalcium aluminate from taking
part in the hardening reactions. When all of the sulfate ions have
been consumed, it is believed that the ettringite converts to a
monosulfate, which does not adhere to the surface of the tricalcium
aluminate particles. Thus as the ettringite converts to the mono-
sulfate, the impervious jacket coating the tricalcium aluminate
breaks up, allowing the tricalcium aluminate to take part in the
hardening reactions, A possible explanation for the accelerating
effect of the admixtures of the present invention is that the com-
pounds either prevent the formation of ettringite or attack and
solubilize the ettringite and lime coatings which retard the har-
dening of tricalcium aluminate. `

PROPERTIES OF CEMENT COMPOSITIONS CONTAINING
ADMIXTURES OF THE PRESENT INVENTION
Accelerating admixtures in accordance with the present
invention may be employed in connection with all uses of portland
cement compositions in which acceleration of the setting time is
desirable. In this section effects of admixtures of the present
invention on cement compositions other than effects on setting
times are discussed.

Salts of the present invention may be made by neutraliz-
ing the selected ~-hydroxy carboxylic acid with the appropriate
base. These salts have an approximately neutral pH and hence are
not caustlc and may be used and processed without taking the spe-
cial safety precautions required in connection with sodium carbon-
ate-sodium aluminate accelerators presently used for shotcreting.
The accelerating admixtures of the invention cause neither
reaction with ferrous metals nor electrolytic action between diff-
erent metals, and are suitable for use in connection with rein-
forced and prestressed concretes as well as other applications.

involving a cement, mortar, or concrete-metal interface
Unlike mortar admixed with sodium carbonate-sodium alu-
minate shotcrete accelerators in commercial use, mortars accele-
rated in accordance with the present invention generally exhibit


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~7~LZ4~

excellent early strength, rendering them especially suitable for
shotcreting since thinner layers of mortar may be used than are
presently required in many such applications.
Accelerating admixtures usually are found to reduce
somewhat the ultimate compressive strength of the hardened compo-
sition relative to the strength of control compositions which con-
tain no admixture, while retarders ordinarily increase the ulti-
mate strength. Accelerators of the present invention also
generally exhibit this behavior. In the case of certain of these
accelerators, however, the reduction in the ultimate strength is
much less than with prior-art accelerators. Figure 2 is a plot
of the compressive strength (ASTM C-109) Atlas cement versus time
(hours), both for the cement alone with no additives and with
potassium hydroxyacetate in concentrations of 3% relative to the
cement. The water-cement ratio was 0.35. Figure 2 shows that the
accelerator admixture enhanced the compressive strnegth somewhat at
times up to 15 hours, and decreases compressive strength slightly
over 15 hours, the acclerated cement achieving a 14-day (336
hour) compressive strength over 80% of that of the plain cement.
An additional application for which the present invention
is particularly suited is as an ingredient in quick-setting-mortar
compounds. As disscussed above, quick-setting-mortar compounds are
widely used to repair damaged concrete. This application requires
shortened setting times and in addition it is desirable that the
ultimate ~trength of the mortar patch be high so that the repair
will be permanent. A quick-setting-mortar compound was prepared
using potassium hydroxyacetate which exhibited a 28-day compres-
sive strength of over 9,000 pounds per squar inch, as measured
by ASTM Test C-109. By contrast, two commercially available quick-
setting-mortar compounds using sodium carbonate-sodium aluminate
accelerators had a 28-day compressive strength of roughly 3,000

pounds per squar inch. Thus quick-setting-mortar compounds can
be made using the present invention which have approximately
- 13 -



~ ~07~4~ -

three times the compressive strength of prior-art quick-setting-
mortar compounds.
Generally admixtures of the present invention function
not only as accelerators but also as water-reducing agents. In a
series of measurements made on a flow table the percent of water
reduction was found to vary as a function of the concentration of
potassium hydroxyacetate in mortar. The percent water reduction
versus concentration curve, shown in Figure 3, exhibits a minimum
near the concentration of 1.5% by weight salt relative to the cem-

ent, which, in this instance, coincides with the crossover point
for this salt. The percent water reduction at this minimum is
appoximately 2.8~. As the concentration of the admixture is in-
creased past the minimum, the percent water reduction also increases.
roughly linearly.
EXAMPLES
The following specific examples of portland cement com-
positions and their effects on setting time will facilitate a
better understanding of the invention.
Example 1
The following mortar was prepared:
Atlas Type 1 Cement---------- 4 lbs.
Federal Fine Sand----------- 10 lbs.
water------------------------ 2 lbs.
potassium hydroxyacetate----- 1.9 Oz.
The concentration of potassium hydroxyacetate relative to the cem-
ent was 3% by weight. The time to initial set of this mortar, as
measured by the Proctor Needle test was 11 minutes.
Example II
Example I was repeated except that 1.9 oz. of sodium
hydroxyacetate, corresponding to 3% by weight salt, was substi-

tuted for the potassium hydroxyacetate. The time to initial set
of this mortar, as measured by the Proctor Needle test, was 5
minutes.


` 107~LZ4~
Example III
Example I was repeated except that 1.9 oz. of the sodium
salt of dl-mandelic acid was substituted for the potassium hydroxy-
acetate. The concentration of the salt relative to the cement was
3.0% by weight. The time to final set of this mortar by the Vicat
test was 1.75 minutes.
Example IV
The following mortar was prepared:
Atlas Type I Cement--------- 4 lbs.
ASTM Concrete Sand---------- 8 lbs.
water----------------------- 1.72 lbs.
sodium hydroxyacetate-----~- 1.9 oz.
The concentration of sodium hydroxyacetate relative to the cement
was 3~ by weight. The mortar is particularly suitable for shot-
crete applications. The time to initial set as measured by the
Proctor N0edle test was 0.45 minutes.
Example V
The following mortar was prepared:
Atlantic Type I Cement------ 10 lbs.
Federal Fine Sand----------- 1 lbs.
water----------------------- 3 lbs.
sodium hydroxyacetate------- 3.68 oz.
The concentration of the salt relative to the cement was 2.3% by
weight. This mortar is particularly suitable as a quick-setting-
mortar compound. The time to final set as measured by the Vicat
Needle method was 5 minutes.
Example VI
The following mortar was prepared:
Atlas Type I Cement--------- 7.8 lbs.
Federal Fine Sand----------- 1.9 lbs.
water----------------------- 2.8 lbs.
sodium lactate-------------- 2.5 oz.

The concentration of the salt relatvie to the cement was 2 percent
by weight. The final setting time as measured by the Vicat Needle

-- 1071Z44

test was two minutes.
Example VII
Mortar of the following proportions was mixed in the
nozzle of a shotcreting rig and sprayed on a vertical wall:
Atlas Type I Cement~ -- 1 part by weight -~
sand----------------------- 3 parts by weight
water---------------------- ,25 parts by weight
sodium hydroxyacetate------ .04 parts by weight
The final setting time of the mortar applied to the wall was less
than one minute as measured by the Proctor Needle test. Core
~amples cut from th~ mortar exhibited a compressive strength of
1080 psi one hour after application, 3870 psi aftereight hours,
and a 28-day ultimate strength of 5520 psi. Mortar containing 3
percent of a conventional sodium aluminate-sodium carbonate accel-
erator typically has a compressive strength of less than 800 psi
in eight hours and an ultimate strength of roughly 3000 psi.
Example VIII
The following mortar was prepared:
Atlas Type I Cement--------- 1 part by weight
Federal Fine Sand----------- 0.2 parts by weight
water----------------------- 0.35 parts by weight
potassium hydroxyacetate---- 0.02 parts by weight
The concentration of potassium hydroxyacetate relative to the
cement was two percent by weight. The time to final set for this
mortar as measured by the Vicat Needle test was 1.1 minutes. This
mortar i8 particularly suitable as a plugging compound.
Example IX
Mortar of the following proportions was prepared:
Atlas Type I Cement--------- 1 part by weight
Federal Fine Sand----------- 2,5 parts by weight
water----------------------- 0.30 parts by weight

aalcium hydroxyacetate------ 0.03 parts by weight
The calcium hydroxyacetate was prepared by neutralzing a 70 per-



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1~71244

cent solution of hydroxyacetic acid with an aqueous solution of
calcium hydroxide. The time to final set of this mortar as -
measured by the Vicat Needle test was 2,5 minutes.
Example X
The following concrete was prepared:
Atlas Type I cement----------- 10 lbs.
Federal Fine Sand------------- lO lbs.
coarse aggregate-------------- 5 lbs.
water------------------------- 3 lbs.
sodium hydroxyacetate--------- 8 oz.
This concrete had a final setting time of 12 minutes as measured
by the Vicat Needle method and a compressive strength of 1060 psi
one hour after mixing. It is particularly suitable as a concrete
patching compound.
It will be recognized by those familiar with this art
that modifications of the foregoing specific examples may be made
without departing from the scope and spirit of the invention, which
i9 limited solely in accordance with the claims hereof. For exam-
ple, instead of using one of the ~-hydroxy carbonyl compounds
recited in this application alone, mixtures of such compounds may
be employed to similar advantage. If a mixture of ~-hydroxy
carbonyl compounds is used, the total concentration of ~- hydroxy
carbonyl compounds relative to the cement must be an accelerating
concentration.




- 17 -