of conventional steel reinforcement in typical reinforced concrete 

 under normal conditions where the bars have sufficient concrete 

 cover. Stannous chloride when properly used acts as an accelerator 

 and does not cause corrosion of the steel even when steam curing 

 is used. 



(4) Calcium Chloride . Calcium chloride is available in two 

 forms. Regular flake calcium chloride, ASTM Standard D98 (type 1), contains 

 a minimum of 77 percent CaCl 2 . Concentrated flake, pellet, or granular 

 calcium chloride ASTM Standard D98 (type 2) contains a minimum of 94 

 percent of CaCl 2 . Calcium chloride can generally be used safely in amounts 

 up to 2 percent by weight of the cement (McCall and Claus, 1953). Larger 

 amounts may be detrimental and, except in rare instances, provide little 

 additional advantage. The benefits of the use of calcium chloride are 

 usually more pronoun ed when it is employed in concrete with a mixing and 

 curing temperature below 21 Celsius (70 Farenheit). At high mixing and 

 curing temperatures long-term strength, especially flexural strength, may 

 decrease, and shrinkage and cracking may increase. 



Laboratory tests have indicated that most increases of compressive 

 strengths of concrete resulting from the use of 2 percent of calcium 

 chloride by weight of cement are in the range of 2 760 to 6 890 kilopascals 

 (400 to 1 000 pounds per square inch) at 1 to 7 days for 21 Celsius 

 curing. At 4.4 Celsius (40 Farenheit) curing the increases in strengths 

 obtained at 1 and 7 days with calcium chloride are in the same range as 

 that for 21 Celsius curing. The increase in strength usually reaches its 

 maximum in 1 to 3 days and thereafter generally decreases. At 1 year, some 

 increase is still evident in concrete made with most cements. The specific 

 effect of the use of calcium chloride varies, however, for different cements 

 as is indicated by the range of strength increases cited above for the 

 early ages. 



The relative increase in flexural strength of concrete resulting from 

 the use of 1 or 2 percent of calcium chloride is not as great as the 

 increase in compressive strength. Calcium chloride increases the flexural 

 strength at 1 and 3 days, but decreases the flexural strength at 28 days or 

 at later ages (McCall and Claus, 1953) . 



Flexural strengths of concretes containing 1 to 2 percent calcium 

 chloride are usually increased over the strengths of similar concrete 

 without the admixture by 40 to 90 percent at 1 day and by 5 to 35 percent 

 at 3 days, respectively, when moist cured at 21 Celsius. At 28 days, 

 decreases of up to 12 percent have been reported from laboratory tests of 

 moist-cured concrete. 



The use of 1 percent calcium chloride by weight of the cement is 

 sufficient in most cases to accelerate setting and increase strength 

 sufficiently for cold weather concreting, with the understanding that cold 

 weather protection is provided. The selection of the optimum amount 

 should be based on the type of cement, the temperature of the concrete, and 

 the ambient air temperature. 



Calcium chloride may promote corrosion of the usual reinforcement in 

 concrete even though adequate concrete cover is provided for the steel. 



91 



