There is a growing realization that the demands being made on the construction industry can only be met if construction activity can be maintained in the winter months. However, concreting requires special attention whenever air temperatures fall below 50 degrees F. at the time of placing. To combat the problem, the Journal of the American Concrete Institute has recommended 1 per cent calcium chloride by weight of cement to accelerate the hydration of cement so that other forms of protection will not be required until temperatures are close to freezing. Calcium chloride assists in maintaining the proper temperature for the hydration of cement. Calcium chloride in concrete increases the rate of early heat development and accelerates the setting of the cement. Calcium chloride also reduces by approximately one half, the time required for cement to reach maximum temperature thus off setting the rapid loss of heat that occurs in winter operations. The increased rate of temperature development is due to the acceleration of the rate of hydration of the cement and is one of the most important results of using calcium chloride. The Journal of the American Concrete Institute also recommends that there be no frozen lumps of material in the concrete as place and that the concrete should be prevented form freezing and drying for at least three days after placing.