Abstract:
A chloride-free admixture for use as a cold weather (e.g., 13° F. to 40° F.) concrete set accelerator. The admixtures comprise; 
     1) at least one soluble inorganic salt having freezing point depressant properties, 
     2) at least one water reducing dispersant, e.g., superplasticizer, 
     3) at least one inorganic early set and strength accelerator, and optionally, 
     4) at least one inorganic set accelerator.

Description:
This is a continuation of application Ser. No. 07/730,321, filed Jul. 15, 1991, which in turn is a continuation of application Ser. No. 07/619,150, filed Nov. 27, 1990, which in turn is a continuation of application Ser. No. 07/527,392, filed May 23, 1990, which in turn is a continuation of application Ser. No. 07/420,204, filed Oct. 12, 1989, which in turn is a continuation of application Ser. No. 07/322,277, filed Mar. 10, 1989, which in turn is a continuation of application Ser. No. 07/091,238, filed Aug. 31, 1987, which in turn is a continuation-in-part of application Ser. No. 06/909,256, filed Sept. 19, 1986, all of which are now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to concrete admixtures. In one particular aspect it relates to concrete admixtures for use as cold weather concrete set accelerators, and to methods for their use. 
     Low or freezing temperatures ( e.g., 40° to 15° F.) presents special problems in mixing, placing and curing of concrete. Concrete may freeze while saturated and subsequently be of low strength, or there may be a slow development of strength. 
     The 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, are mandatory. Protective insulating coverings, heating 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 concrete 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 admixtures which are, (1) non-corrosive, and (2) meet or exceed the rate-of-hardening and compressive strength performance at about 13° to 40° F., of a plain concrete mix at 50° F. 
     The present invention provides admixture compositions which meet these prior art limitations. 
    
    
     THE INVENTION 
     Broadly, the present invention provides a chloride-free admixture for use as a cold weather concrete set accelerator which comprises 
     (1) 100 parts by weight of at least one soluble inorganic salt having freezing point depressant properties, 
     (2) from 13.3 to 30 parts by weight of at least one water-reducing dispersant, e.g., superplasticizer, 
     (3) from 3 to 30 parts by weight of at least one inorganic early set and strength accelerator, and 
     (4) from 0 to 10 parts by weight of at least one organic set accelerator. 
     Preferably the quantity of component 2 should be greater than 15 parts by weight. 
     Preferably the quantity of component 3 is from 5 to 10 parts by weight. 
     Preferably component 4 is present in an amount of from 1.3 to 6 parts by weight. 
     The proportions given above are parts by dry weight of the total weight of components 1-4, neglecting any water which may be present. The admixture of the invention may be added as a solid direct to the concrete mix water. Preferably the admixture is in the form of an aqueous solution. 
     The set accelerating admixtures of this invention combine two beneficial effects: 
     (1) They depress the mix water freezing point, so that a concrete mix will not freeze during the first few critical hours of curing at temperatures below 32° F., 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. 
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Component 1 is preferably selected from ammonium, alkali and alkaline earth nitrates and nitrites, more preferably from calcium and sodium nitrate and nitrite. Calcium nitrate is particularly preferred. Up to 50% of the inorganic salt of component 1 may be replaced by urea. 
     Component 2 is preferably an alkali or alkaline earth salt of a napthalene sulphonate/formaldehyde condensate, more preferably a sodium or calcium salt or an acrylic copolymer, e.g., poly[hydroxy ethyl methacrylate/acrylic acid]. Particularly preferred is napthalene sulphonate/formaldehyde condensate in sodium salt form. 
     Component 3 is preferably selected from ammonium, alkali or alkaline earth thiocyanates and thiosulphates, more preferably from calcium, ammonium and sodium thiocyanates. Particularly preferred is sodium thiocyanate. 
     Component 4 is preferably selected from methylolgylclurils, 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. More preferably, component 4 is selected from methylolglycolurils, e.g., tri(N-methylol)glycoluril and tetra (N-methylol)blydoluril, particularly tetra (N-methylol)glycoluril. 
     A preferred admixture according to the invention consists of (1) calcium nitrate, (2) sodium salt of naphthalene sulphonate/formaldehyde condensate, (3) sodium thiocyanate and (4) tetra(N-methylol)glycoluril, in the proportions by weight: 100 parts (1), 20 parts (2), 6.7 parts (3) and 4 parts (4). This preferred admixture is preferably used in the form of an aqueous solution containing 40%-60% dry weight of components 1-4, particularly 50% wt. 
     The admixtures of the invention may be used over a wide range of temperatures from about 70° F. to about -5° F. The amount of admixture which is added to the concrete may be from 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). For the above preferred admixture, the dose range is from 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/100 parts cement of the preferred admixture will prevent a concrete mix from freezing at temperatures down to about -6° F., 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 motors 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, comprising adding to the mix from 0.13 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 mortar so obtained will contain the following amounts of components 1-4, defined above: 
     
         ______________________________________Component        parts/100 parts cement______________________________________1                0.5-4.02                0.1-0.83                0.033-0.64                0.0-0.16            preferably 0.02-0.16Preferred amounts are:1                2.0-3.02                0.4-0.63                0.1-0.64                0.04-0.12______________________________________ 
    
     A similar method which may be substituted for that already described, comprises adding to the concrete or cement mortar 
     (A) 0.5 to 4% by weight of cement of at least one component 1), 
     (B) 0.1 to 0.8% by weight of cement of at least one component 2), 
     (C) 0.033 to 0.6% by weight of cement of at least one component 3), and 
     (D) 0 to 0.16% of cement of a least one component 4). 
     In the preferred method, at least one component 4) is added in the amount of from 0.02 to 0.16% wt. of cement. 
     In the Example the following terms are used in the Tables. 
     
         ______________________________________Formula  Plain refers to a concrete mix without    admixture. It is used as a reference.    The letters A to CC refer to the admixture    formulas set out in the chart below.Dose     Amount of admixture added in fluid ounces    per 100 lbs. of cement.Slump    The drop in inches of a 12 inch cone. ASTM C 143Air      The percent of entrained air.Water Red    Refers to the amount in % of water reduced    from the plain concrete mix. The amount    listed for the plain mix is the initial    starting amount in lbs./cu. yd.PSI/Percent    PSI = pounds per square inch of compressive    strength of a concrete sample.    The percent is the percent of increase    or decrease of breaking strength based    on the plain mix at 100%.Micro-Air    An admixture for entraining air in concrete.    The admixture meets the requirements of    ASTMC-260, AASHTO M-154 and CRD-C13.    (Master Builders - Cleveland OH).MB-VR    An admixture for entraining air in concrete.    (Master Builders Neutralised VINSOL).    The admixture meets the requirements of    ASTM C-260, AASHTO M-154 and CRD-C13.ROH      Rate of Hardening. The time in hours    to reach initial set. For plain concrete    it is the actual time in hours to reach    initial set. The ROH for admixture concrete    is the difference in set time between    plain and admixture concrete.    ROH of admixture minus ROH of plain equals    relative ROH of admixture concrete.    ASTM C 403-80.______________________________________ 
    
     All concrete mixes were based on a cubic yard formula of about 4000 lbs. 
     (1) Cement (Type I) 517 lbs. 
     (2) Sand and Stone about 3200 lbs. Sand to Stone ratio of 40:60 to 50:50. The stone used was 1/4 in. topsize crushed limestone. 
     (3) Water as indicated in the Tables. 
     4) Admixture as indicated in the Tables. 
     The procedure for the experiments was as follows: 
     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 cut 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. 
     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. 
     
         __________________________________________________________________________ADMIXTURE FORMULATIONSFORMULA/POUNDS PER 100 LBS. OF CEMENT__________________________________________________________________________Materials   A  B  C  D  E  F  G  H  I  J  K__________________________________________________________________________(1) Calcium nitrate       3.500          3.000             3.000                3.000                   3.000                      3.000                         3.000                            3.000                               3.000                                  2.500                                     2.500(2) Sodium salt of       0.700          0.600             0.600                0.600                   0.600                      0.400                         0.400                            0.400                               0.400                                  0.500                                     0.500naphthalene sulfo-nate-formaldehyderesin(3) Sodium thiocyanate       0.233          0.600             0.600                0.200                   0.200                      0.600                         0.600                            0.200                               0.200                                  0.400                                     0.167(4) Tetra (N-methylol)       0.117          0.120             0.049                0.120                   0.040                      0.120                         0.040                            0.120                               0.040                                  0.080                                     0.100glycoluriel(5) Water   Added to give dose rate indicated in the Tables.__________________________________________________________________________Materials   L  M  N  O  P  Q  R  S  T  U  V__________________________________________________________________________(1) Calcium nitrate       2.000          2.000             2.000                2.000                   2.000                      2.000                         2.000                            2.000                               2.000                                  1.500                                     1.000(2) Sodium salt of       0.600          0.600             0.600                0.600                   0.400                      0.400                         0.400                            0.400                               0.400                                  0.300                                     0.200naphthalene sulfo-nate-formaldehyderesin(3) Sodium thiocyanate       0.600          0.600             0.200                0.200                   0.600                      0.200                         0.200                            0.133                               0.060                                  0.100                                     0.66(4) Tetra (N-methylol)       0.120          0.040             0.120                0.04                   0.04                      0.120                         0.040                            0.080                               0.120                                  0.060                                     0.04glycoluriel(5) Water   Added to give dose rate indicated in the Tables.__________________________________________________________________________Materials    W  X   Y  Z   AA  BB   CC  DD__________________________________________________________________________(1) Calcium nitrate        3.000           3.000  2.000                      3.000                          3.000                               3.000                                   3.000(1) Calcium nitrate 3.000                  1.000(2) Calcium Napthalene        0.600           0.600Sulfonate(2) Napthalene Sulfonate               0.600                  0.600                      0.600                          0.600                               0.600                                   0.600formaldehydeCondensate(3) Sodium Thiocyanate        0.200  0.200                  0.200                      0.200                          0.200                               0.200                                   0.200(4) Tetra (N-Methylol)        0.120           0.120               0.120                  0.120Glycoluriel(4) Ammonium    0.200Thiocyanate(4) Pyruvic Aldehyde        0.1200(4) Glutaraldehyde                   0.1200(4) N-Hydroxyethyl-             0.1200pyridine(4) N-N-Bis(2-Hydroxy-                   0.1200ethyl) PiperazineSodium Acetate*        0.042           0.042               0.042                  0.042                      0.042                          0.042                               0.042                                   0.042Water        Added to give dose rate indicated in the tables__________________________________________________________________________ *Sodium Acetate  buffering agent to maintain concrete pH from Ph 4-7. 
    
     EXAMPLE 
     The results of Tables I to VI show that the admixture compositions of this invention are capable of protesting concrete systems against freezing down to 16° F. Table VI shows that the admixtures also give satisfactory results when used at temperatures up to 70° F. 
     
                                           TABLE I__________________________________________________________________________                        PSI/PercentTrial   Formula    Dose       Slump           Air              ROH Water Red.                        1 Day                            3 Day                                7 Day                                     28 Day__________________________________________________________________________0  Plain -- 7.25           6.8              Frozen                  286.0 lbs.                         54 353 1050 2732   Micro-Air    0.65                100 100 100  1001  CaCl.sub.2    2.00       7.50           5.9              Frozen                  -4.9% 100 671 1775 4513   Micro-Air    0.59                185 190 169  1652  U     45.00       7.50           6.8              5.500*                  -4.9% 134 647 1762 4279   Micro-Air    0.77                248 183 168  1573  D     90.00       7.00           6.0              5.130*                  -5.2% 164 852 2718 4979   Micro-Air    0.74                304 241 259  182__________________________________________________________________________ All concrete samples (0 to 3) were made at 40° F., placed at 20° F., and cured at variable temperatures of from 6° to 66° F. *actual times 
    
     
                                           TABLE II__________________________________________________________________________                        PSI/PercentTrial   Formula   Dose       Slump           Air              ROH Water Red.                        1 Day                            3 Day                                 7 Day                                      28 Day__________________________________________________________________________0  Plain   --  5.00           1.9              7.82                  296.0 lbs.                        399 1675 2961 5259                        100 100  100  1001  A    105.00       5.00           3.0              -4.57                  10.1% 388 1234 3201 6347                        97  74   108  1212  D    90.00       5.25           2.7              -4.20                  9.8%  390 1091 3208 6369                        98  65   108  1213  K    75.00       5.00           2.3              -4.20                  7.1%  303 675  2815 5200                        76  40   95   994  S    60.00       5.00           2.2              -4.32                  9.5%  409 834  3190 5641                        103 50   108  1075  U    45.00       5.00           1.8              -3.07                  7.1%  393 800  2339 5284                        98  48   96   100__________________________________________________________________________ Trial #0 Plain concrete made and cured at 50° F.  Trials #1-5 concrete samples made at 50° F., cured at 16-20° F. for 3 days, then cured at 50° F. 
    
     
                                           TABLE III__________________________________________________________________________                          PSI/PercentTrial   Formula    Dose Slump             Air                ROH Water Red.                          1 Day                              3 Day                                   7 Day                                        28 Day__________________________________________________________________________0  Plain --   4.75             5.0                10.50                    290.0 lbs.                          284 1565 3071 5460   Micro-Air    0.81                  100 100  100  1001  J     100.00         5.25             6.0                -5.87                    -9.0% 297 1125 4384 6604   Micro-Air    0.81                  105 72   143  12199 Alternate    --   5.00             5.8                5.00                    -1.0% 140 487  1550 3675   Plain 0.81                   49 31   50   67   Micro-Air__________________________________________________________________________ Trial #0, concrete samples made and cured at 50° F. Trials #1 and 99, concrete samples made at 50° F., placed at 28° F., and cured at 28° F. for 1-3 days. All 7 and 28 day samples cured at 50° F. 
    
     
                                           TABLE IV__________________________________________________________________________                        PSI/PercentTrial   Formula   Dose.sup.(1)       Slump           Air              ROH Water Red.                        1 Day                            28 Day__________________________________________________________________________0  Plain   --  4.88           1.6              8.75                  298.0 lbs.                        353 4959                        100 1001  B        5.00           2.8              -4.87                  9.4%  328 6311                        93  1282  C        5.25           3.3              -4.75                  8.7%  228 6462                        65  1303  D        5.25           3.1              -4.62                  12.1% 269 6425                        76  1304  E        5.25           3.0              -4.75                  6.7%  228 6659                        65  1345  F        5.25           2.4              -5.00                  5.0%  294 5900                        83  1196  G        5.00           2.7              -5.00                  9.4%  225 7125                        64  1447  H        5.00           2.5              -4.87                  8.7%  276 6578                        78  1338  I        5.00           2.8              -5.37                  6.4%  266 6217                        75  1269  J        5.19           2.8              -4.87                  9.1%  292 6378                        83  12910 L        5.25           3.1              -4.37                  14.1% 318 6812                        90  13711 M        5.25           3.5              -4.87                  11.7% 287 7112                        81  14312 N        5.50           2.9              -4.25                  11.7% 269 6184                        76  12513 O        5.25           2.9              -4.37                  13.4% 232 6234                        66  12614 P        5.00           2.4              -4.62                  6.7%  266 6219                        75  12515 Q        5.00           2.5              -4.75                  7.4%  256 6212                        73  12516 R        5.25           2.7              -4.50                  8.1%  209 6081                        59  12317 T        5.25           2.9              -4.50                  9.4%  209 5787                        59  117__________________________________________________________________________ Trial #0, concrete samples made, poured and cured at 50° F. Trials #1 to 17 concrete samples made 50° F., placed and cured at 24° F. for one day, and then cured at 50° F. .sup.(1) Admixture diluted with water up to a convient amount. 
    
     
                                           TABLE V__________________________________________________________________________                        PSI/PercentTrial   Formula   Dose       Slump           Air              ROH Water Red.                        1 Day                             3 Day                                  7 Day                                       28 Day__________________________________________________________________________0  Plain   --  3.00           5.7              5.375                  267.0 lbs.                        1169 2887 4281 5550   MB-VR   1.00                 100  100  100  1001  V    30.00       2.00           5.2              -2.125                  6.7%  1909 4056 5697 7234   MB-VR   1.64                 163  140  133  1302  S    60.00       2.25           6.0              -2.625                  8.2%  2041 4268 5684 6919   MB-VR   1.59                 175  160  133  1253  D    90.00       2.25           6.4              -2.875                  10.5% 2506 5228 6078 7584   MB-VR   1.49                 214  181  142  137__________________________________________________________________________ Trials #0 to 3 concrete samples were all made, placed and cured at 70° F. 
    
     
         __________________________________________________________________________                         PSI/PercentTrial   Formula    Dose.sup.(1)        Slump            Air               ROH Water Red.                         3 Day                              7 Days                                   28 Days__________________________________________________________________________0  Plain 0.88        6.75            5.1               Frozen    915  2206 4206   Micro-Air    0.88        6.75             100  100  1001  W         6.38            7.4               4.625                   -12.3%                         2548 4486 5787                         278  203  1372  X         6.00            7.8               3.625                   -15.8%                         2693 4486 5898                         294  203  1403  Y     0.58        6.50            5.5               5.125                   -9.5% 2198 3722 5401   Micro-Air                  240  169  1304  Z     0.66        6.30            5.8               5.875                   -10.5%                         2383 4373 5646   Micro-Air                  260  198  1345  AA    0.35        6.25            5.9               6.5 -12.6%                         2314 5051 7118   Micro-Air                  253  229  1696  BB        6.25            6.9               6.0 -12.3%                         2726 5146 6678                         298  233  1597  CC        6.63            5.8               5.625                   -10.5%                         2512 4678 6196                         275  212  1478  DD    0.40        6.50            5.3               6.750                   -8.1% 2448 4558 5925   Micro-Air                  268  207  14199 Plain     6.38            5.3               5.380     1125 2207 3962__________________________________________________________________________ Samples 0-8 were made at 35-40° F. cured at variable temperatures from 20-40° F. (3 Day Cure 20-33 F) Samples 99 (Plain) made and cured at 50° F.