CA1278797C

CA1278797C - Concrete admixture compositions

Info

Publication number: CA1278797C
Application number: CA000547111A
Authority: CA
Inventors: John W. Brook
Original assignee: Sandoz AG
Current assignee: Construction Research and Technology GmbH
Priority date: 1986-09-19
Filing date: 1987-09-17
Publication date: 1991-01-08
Anticipated expiration: 2008-01-08
Also published as: ATA235987A; AU7848087A; AU592013B2; GB2195328B; BE1002419A4; JPS6389445A; FR2604170B1; CH675716A5; GB2195328A; IT8748397A0; FR2604170A1; AT393498B; IT1211786B; GB8721701D0; ES2005013A6; DE3730527A1

Abstract

CONCRETE ADMIXTURE COMPOSITIONS

Abstract of the Disclosure A chloride-free cold-weather set accelerator for concrete and cement mortar comprises A) 100 parts by weight of at least one soluble inorganic salt having freezing point depressant properties B) from 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) from 0 to 10 parts by weight of at least one organic set accelerator.

Description

1~78~7~3~7 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 ~'~7~3~797 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.

~78~7~7 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~

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 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 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 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 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 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 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 1'~78~97 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 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.

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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.

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Claims

1. A chloride-free admixture for use as a cold weather concrete set accelerator which ccmprises A) 100 parts by weight of at least one soluble inorganic salt having freezing point depressant properties, up to 50% wt.
of which may be replaced by urea B) from 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) from 0 to 10 parts by weight of at least one organic set accelerator.

2. An admixture according to Claim 1 comprising 100 parts by weight A), from above 15 to 30 parts by weight B), 5 to 10 parts by weight C) and 1.3 to 6 parts by weight D).

3. An admixture according to Claim 1 in which component A is selected from ammonium, alkali and alkaline earth nitrates and nitrites.

4. An admixture according to Claim 3 in which component A is calcium nitrate,

5. An admixture according to Claim 1 in which component B is an alkali or alkaline earth salt of a naphthalene sulphonate/formaldehyde condensate or a sulphonated melamine/formaldehyde condensate, or an acrylic copolymer.

6. An admixture according to Claim 5 in which component B is naphthalene sulphonate/formaldehyde condensate in sodium salt form.

7. An admixture according to CLaim 1 in which ccmponent C is selected from ammonium, alkali or alkaline earth thiocyanates and thiosulphates.

8. An admixture according to Claim 7 in which component C is sodium thiocyanate.

9. An admixture according to Claim 1 in which component D is selected from methylolglycolurils, dimethylolurea, mono- and di-(N-methylol) hydantoin, mono- and di-(N-methylol) dimethylhydantoin, N-methylolacrylamide, tri-(N-methylol) melamine, N-hydroxyethylpiperidine, N,N-bis(2-hydroxyethyl)piperazine, glutaraldehyde, pyruvaldehyde, furfural and water soluble urea-formaldehyde resins.

10. An admixture according to Claim 9 in which component D is tetra(N-methylol)glycoluril.

11. An admixture according to Claim 2 ccmprising A) 100 parts by weight calcium nitrate B) 20 parts by weight naphthalene sulphonate/formaldehyde condensate sodium salt C) 6.7 parts by weight sodium thiocyanate and D) 4 parts by weight tetra(N-methylol)glycoluril.

12. An admixture according to Claim 1 in the form of an aqueous solution.

13. A method for accelerating the set of a concrete or cement mortar mix, suitable for use in cold weather conditions, comprising adding to the mix from 0.13 to 5.6 parts (dry weight) of an admixture according to Claim 1 per 100 parts dry weight of cementitious material in the mix.

14. A method for accelerating the set of a concrete or cement mortar mix, suitable for use in cold weather conditions, comprising adding to the concrete or cement mortar 1) 0.5 to 4 % by weight of cement of at least one component A), 2) 0.1 to 0.8 % by weight of cement of at least one component B), 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 which components A, B, C and D are as defined in Claim 1.

15. A concrete or cement mortar mix containing 1) 0.5 to 4 % by weight of cement of at least one component A), 2) 0.1 to 0.8 % by weight of cement of at least one component B), 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 which components A, B, C and D are as defined in Claim 1.

16. A concrete or cement mortar mix according to Claim 15 containing 0.02 to 0.16 % wt. of component D.

17. A concrete or cement mortar mix according to Claim 16 containing 2.0-3.0 % wt. of component A, 0.4-0.6 % wt. of component B, 0.1-0.6 % wt. of component C and 0.04-0.12 % wt. of component D.