Cold weather concreting can be a gamble. Freezing at an early age may damage the concrete. Even if the concrete doesn't freeze, low temperatures retard the set and increase waiting time before finishing. Forms can't be stripped as fast and strength develops slowly. Until recently, the only way to protect concrete from freezing was with insulated curing blankets or heated enclosures. Now there's a new way, using a specially formulated admixture.
A low-temperature accelerator is now available for use in concrete placed at and exposed to ambient temperatures below freezing. The admixture speeds up setting while increasing early and ultimate strengths. Concrete containing this admixture can also be placed at temperatures as low as 20 degrees Fahrenheit without freezing.
The low-temperature accelerator is recommended for use during cold weather concreting of slabs, columns, beams, or other structural members. For exterior concrete that will be exposed to freezing and thawing, an air-entraining admixture should be used in addition to the accelerator.