Note: Descriptions are shown in the official language in which they were submitted.
1~78~7~3~7
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CONCRElE ADMIXTURE CCMPC6ITIoNS
This invention relates to concrete admixtures for use as cold
weather concrete set accelerators.
Low or freezing temperatures (e.g. 5C to -7C) present special
problems in the mixing, pouring and curing of concrete. Concrete may
freeze while saturated and su~sequently be of low strength, or there
may be a slow develcpnent of strength.
m e American Concrete Institute (ACI) Report 306R-78 on Cold
Weather concreting, sets forth standard practices to prevent freezing
and assure the safe development of concrete strength during curing at
ambient freezing conditions. Heating of materials, including mix
water and aggregates is mandatory. Protective insulating coverings,
heated enclosures and proper curing conditions are described.
An additional factor (not often reported) associated with
freezing temperatures, is the distress of the concrete worker
operating under adverse conditions. Even if dressed warmly, the
conrete worker wishes to finish a pour or complete the finishing as
fast as possible, and move indoors out of the wind and cold. Thus, an
accelerated set time is an important aspect of cold weather
concreting.
While the prior art has addressed the problems of using
concrete in cold weather (e.g. the use of calcium chloride as the
principle accelerating admixture), it has not successfully developed
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admixtures which are, (1) non-corrosive, and (2) meet or exceed at
-10C to 5C the rate-of-hardening and compressive strength
performance of a plain concrete mix at 10C.
It has now been found that set accelerating admixtures in
specific proportions can be obtained which conbine two beneficial
effects:
1) They depress the mix water and pore water freezing point,
so that a concrete mix will not freeze during the first
few critical hours of curing at temperatures below 0C and
2) They reduce the quantity of mix water necessary for
curing, which improves early concrete strength
development. The reduction in mix water also has an effect
on freezing point depression, because it allows for a more
concentrated solution of the admixture.
Accordingly, the present invention provides a chloride-free
admixture for use as a cold weather concrete set accelerator which
comprises
A) 100 parts by weight of at least one soluble inorganic salt
having freezing point depressant properties
B) frcm 13.3 to 30 parts by weight of at least one
superplasticizer
C) from 3 to 30 parts by weight of at least one inorganic
early set and strength accelerator, and
D) frcm 0 to 10 parts by weight of at least one organic set
accelerator.
Preferably the quantity of component B should be greater than
15 parts by weight.
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Preferably the quantity of camponent C is from 5 to 10 parts by
weight.
Preferably ccmponent D i5 present in an amount of fram 1.3 to 6
parts by weight.
The proportions given above are parts by dry weight of the
total dry weight of camponents A-D, neglecting any water which may be
present. The admixture of the invention may be added as a solid
direct to the concrete mix water, or may be used in aqueous solution
for addition to the mix water. Preferably the admixture is in the
form of an aqueous solution.
Camponent A is preferably selected fram ammonium, alkali and
alkaline earth nitrates and nitrites, more preferably fram calcium
and sodium nitrate and nitrite. Calcium nitrate is particularly
preferred. Up to 50% of the inorganic salt of camponent A may be
eeplaced by urea.
Camponent B is preferably an alkali or alkaline earth salt of a
naphthalene sulphonate/formaldehyde condensate or a sulphonated
melamine/formaldehyde condensate, more preferably a sodium or calcium
salt, or an acrylic copolymer for example poly(hydroxyethyl
methacrylate/acrylic acid). Particularly preferred is naphthalene
sulphonate/formaldehyde condensate in sodium salt form.
Camponent C is preferably selected from ammonium, alkali or
alkaline earth thiocyanates and thiosulphates, more preferably from
calcium, ammonium and sodium thiocyanates and thiosulphates.
Particularly preferred as camponent C is sodium thiocyanate.
Component D is preferably selected fram methylolglycolurils,
dimethylolurea, mono- and di-(N-methylol) hydantoin, mono- and
di-(N-methylol) dimethylhydantoin, N-methylolacrylamide,
tri-(N-methylol) melamine, N-nydroxyethylpiperidine,
N,N-bis(2-hydroxyethyl)piperazine, glutaraldehyde, pyruvaldehyde,
furfural and water soluble urea-formaldehyde resins. More preferably,
1~78~9~
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ccmponent D is selected from methylolglycolurils, e.g.
tri-(N-methylol)glycoluril and tetra (N-methylol)glycoluril,
particularly tetra (N-methylol)glycoluril.
A preferred admixture accordincl to the invention consists of A)
calcium nitrate, B) sodium salt of naphthalene sulphonate/
formaldehyde condensate, C) sodium thiocyanate and D)
tetra(N-methylol)glycoluril, in the proportions by weight given
above. Particularly preferred is a mixture of the above four
ccmponents in the proportions by weight: lO0 parts A), 20 parts B),
6.7 parts C) and 4 parts D). This preferred admixture is preferably
used in the form of an aqueous solution containing 40-60~ dry weight
of ccmponents A-D, particularly 50% wt.
The admixtures of the invention may be used over a wide range
of temperatures from about 20C to about -15C. The amount of
admixture which is added to the concrete may be frcm 0.13 to 5.6
parts (dry weight) per 100 parts dry weight of cementitious material
in the concrete (e.g. portland cement plus pozzolanic material such
as fly ash) preferably 0.65 to 5.6 parts. For the above preferred
admixture, the dose range is frcm 1.3 to 4.6 parts / 100 parts
cement, and the lower the ambient temperature the higher will be the
dosage required. Thus a dosage of 2.6 parts / lO0 parts cement of the
preferred admixture will prevent a concrete mix frcm freezing at
temperatures down to about -10C, while for lower temperatures a
dosage of 3.9 parts / 100 parts cement is preferred.
While the admixture of the invention may be used with any of
ASTM type I to V cements, types I and II are preferred. The
admixtures may be used in cement mortars as well as in concrete.
The invention also provides a method for accelerating the set
of a concrete or cement mortar mix, suitable for use in cold weather
conditions, ccmprising adding to the mix frcm 0.65 to 5.6 parts (dry
weight) of an admixture according to the invention per 100 parts dry
weight of cementitious material in the mix. The concrete or cement
1'~7~3'737
- S - 154-0092
mortar so obtained will contain the following amounts of components
A-D, defined above:
CcmPonent ~arts / 100 parts cement
A 0.5 - 4.0
B 0.1 - 0.8
C 0.033 - 0.6
D 0.0 - 0.16,
preferably 0.02 - 0.16
Preferred amounts are:
Component parts / 100 parts cement
A 2.0 - 3.0
B 0.4 - 0.6
C 0.1 - 0.6
D 0.04 - 0.12
Consequently, a similar method which may be substituted for
that already described, conprises adding to the concrete or cement
mortar
1) 0.5 to 4 % by weight of cement of at least one component
A),
20 2) 0.1 to 0.8 % by weight of cement of at least one component
~),
3) 0.033 to 0.6 % by weight of cement of at least one
component C) and
4) 0 to 0.16 % of cement of at least one component D.
In the preferred method, at least one ccmponent D is added in
the amount of frcm 0.02 to 0.16 % wt. of cement.
The following Examples illustrate the invention. All parts and
percentages are by weight unless indicated otherwise.
78'797
- 6 - 154-0092
Examples
Standard procedure
A concrete mix without addition of any admixtures of the
invention (herein referred to as plain reference) is prepared
according to the following formulation:
ccmponent Kg / m_ of concrete
Cement of ASTM type I 307
Aggregate 1900
(Sand to stone ratio of 40:60 to
50:50; the stone used is about 2 cm
topsided crushed limestone)
W~ter as indicated in Tables III to
VII.
An air-entraining admixture may also be added. Those used are
sold by Master Builders Inc. (Cleveland, Ohio) under the trade marks
Micro-Air, and Master ~uilders Neutralised Vinsol, respectively. Both
meet the requirements of ASTM C-260, AASHTO M-154 and CRD-C13.
Concrete mixes with addition of admixtures of the invention are
prepared according to the concrete formulation of the plain
reference. Mixing together the concrete component and the admixtures
is carried out as follows:
Mix water in the amount of about 80 % of that of the plain
reference is added to a conventional cement mixer and the admixture
then added to the water. The cement, sand and stone are further added.
Then the remaining 20 % of water is used in part to adjust the
slump to the slump of the plain reference.
l~7a~7~7
- 7 - 154-0092
The concrete is then poured into 10 cm cubes which are covered
to prevent moisture loss. The concrete cubes are stored for the time
and at the temperature indicated in Examples I to VI.
Properties
The following properties are routinely measured:
Slump, i.e. the drop in cm of a 12 inch (30.5 cm) high cone
of the fresh mix. (ASTM C 143)
Percent~ge of entrained air
~ater Reduction i.e. the difference between the amount of water used
in the plain reference and the (smaller) amount of
water used in the test sample in order to obtain the
same slump, expressed as a percentage of the amount
of water used in the plain reference.
Cqqpressive Strength,
expressed in Kg/cm2 and as a percentage of the
campressive strength of the plain reference measured
under the same conditions.
Rate of ~ardening (~CH),
i.e. the time in hours to reach the initial set.
(ASTM C 403)
1'~78'7'~37
- 8 - 154-0092
Examples 1-26
Tables I and II list admixture formulations according to the
invention, given as parts by weight of components B), C) and D per
100 parts by weight of component A). These formulations are each
dissolved in water such that the aqueous solution contains 3 lb
(1 36 kg) of component A) in 90 flui~ ounces (2.56 litres) of
solution. AS the specific gravity of these solutions is approx. 1.39,
the solutions of the admixture formulations all contain 1.36 kg
component A) in 3.56 kg solution, or 38% by wt. component A). With
the other components, the solutions contain a total of approx.
50% wt. active material.
1~78~ 37
- 9 - 154-0092
Table I
Admixtures 1-18, each containing 100 parts by weight of calcium
nitrate A), and in addition:
parts by weight
B) Na salt of naphthalene C) sodium D) tetra(N-
Example No. sulphonate/formaldehyde thiocya- methylol)
nate glycoluril
1 20 6.7 3.3
2 20 20 4
3 20 20 1.6
4 20 6.7 4
6.7 1.3
6 13.3 20 4
7 13.3 20 1.3
8 13.3 6.7 4
9 13.3 6.7 1.3
16 3.2
11 30 30 6
12 30 30 2
13 30 10 6
14 30 10 2
16 20 10 6
17 20 10 2
18 20 3 6
1'~78~97
- 10 - 154-0092
Table II
Admixtures 19-26
Formulation tparts by weight)
Example No. 19 20 21 22 23 24 25 26
Camponent
A) Calcium nitrate 100 100 - 66.7 100 100 100 100
calcium nitrite -- 100 33.3 - - - -
B) naphthalene
sulphonate/
formaldehyde
Ca salt 20 20
Na salt - - 20 20 20 20 20 20
C) Sodium thiocyanate 6.7 - - 6.7 6.7 6.7 6.7 6.7
Ammonium thiocyanate - 6.7 6.7
D) tetra(N-methylol)
glycoluril 4 4 4 4
pyruvic aldehyde - - - - 4
glutaraldehyde - - - - - - 4
N-hydroxyethyl
piperidine - - - - - 4
N,N'-bis-(2-hydroxy-
ethyl)piperazine - - - - - - - 4
Sodium acetate 1.4 1.4 1.4 1.4 1.4 1.4 1.4 1.4
(buffer)
1'c:7~7~37
- 11 - 154-0092
In the following Examples, the admixture solutions are added to
the test concrete in quantities sufficient to give the indicated
dose, given as parts by weight of total admixture (excluding water~
per 100 lb of cement.
Example 27
An outdoor experiment was carried out in which all the concrete
samples, including the plain concrete reference, were mixed at 5C
and poured at -7 to -8C. During the curing time, the outdoor
temperature varied from -15C to +18C.
The results are indicated in Table III. Trial 1 shows the
optimum results which are obtained with the already known corrosive
CaC12 admixture while trials 2 and 3 demonstrate that similar results
can be obtained when using a non-corrosive admixture of the invention.
Example 28
Plain concrete is made, poured and cured at 10C while concrete
samples of trials 1 to 5 are made at 10C, cured at -8 to -6C for 3
days and then cured at 10C.
In the trials, the admixtures of examples 1 and 4 (of very
similar composition) are added in dosages of from approx. 2 to 4.5
parts/100 parts cement. In all cases the rate of hardening is more
rapid than that of the plain concrete at 10C, and the 2B day
compressive strength is as good as that of the plain concrete.
87~37 1 54-0092
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- 14 - l54-oog2
Example 2g
Two plain concrete samples are prepared, one of which (trial 0)
is made, poured and cured at 10C, while the other (trial 1) is made
at 10C, then poured and cured for 3 days at -3C, then further cured
at 10C. Trial 2 is as trial 1, but contains 3.48 parts / 100 parts
cement of the admixture formulation of Example 10. The results are
shcwn in Table V.
Example 30
A plain concrete sample is made, poured and cured at 10C while
concrete samples of trials 1 to 17 are made at 10C, poured and cured
for 1 day at -5C; then the 28 day samples are cured at 10C.
Results shown in Table VI demonstrate that, compared to the
plain concrete reference, the time to reach the initial setting (rate
of hardening) of trials 1 to 17 is largely reduced, and that the
campressive strength performances after 28 days are superior. The
trial samples did not freeze at the -5C temperature.
Example 31
The plain concrete and concrete of trials 1 to 3 ~containing
the admixture of Example 4) are all made, poured and cured at 21C.
Results are shown in Table VII. The admixtures of the invention
are shown to be effective at this higher temperature.
Example 32
Two plain concretes are prepared. One (trial 0) is made and
cured at 10C. The other one (trial 1), like the concrete samples of
trials 2 to 9, is made at 3-5C, cured for 3 days at a temperature
which varies from -15 to 0C, and then cured at a temperature which
varies fram -15 to 5C.
Results are shown in Table VIII.
8797
- 1 S - 1 54-0092
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