Cold weather concrete has superior properties to concrete placed in hot weather. At low temperatures, though, concrete sets and gains strength more slowly because the cement doesn't hydrate as fast. Setting time is increased about one-third for each 10 degree decrease in concrete temperature down to 40 degrees Fahrenheit. Accelerating admixtures can help to offset these effects of low temperatures on setting and strength gain. They should meet the requirements of ASTM C 494, Standard Specifications for Chemical Admixtures for Concrete.