Problems Encountered in Cold Weather Concreting:

Subsequent problems are encountered during concreting in cold weather conditions:

Delayed Setting

Temperature affects the rate of hydration of cement. If the temperature is low, concrete will take long time to set and harden.

At low temperatures, the development of concrete strength is retarded as compared to the strength development at normal temperatures. The setting period necessary before removal of formwork is, thus, increased. Although the initial strength of concrete is lower, an ultimate strength will not be severely affected provided the concrete has been prevented from freezing during its early life.

The speed of progress of work will be very slow and the economy will be affected in case of cold weather concreting.

Early Freezing of Concrete

When the temperature is sub-zero the free water in the plastic concrete freezes. This freezing prevents the hydration of cement and also makes the concrete expand. That will expansion affects the strength of concrete.

Plastic concrete may suffer permanent damage if it is exposed to freezing temperature. If the concrete is allowed to freeze before a certain pre-hardening period, it might suffer irreparable loss in its properties so much so that even one cycle of freezing and thawing during the pre-hardening period may reduce compressive strength to 50% of what would be expected for normal temperature concrete. The pre-hardening period depends upon the type of cement and environmental conditions. It may be specified in terms of time required to attain a compressive strength of the order of 3.5 to 7 MPa; alternatively it can be specified in terms of period varying from 24 hours to even three days depending upon the degree of saturation and water-cement ratio.

Stresses Due to Temperature Differential

A cracking of concrete may take place due to a large temperature differential. It has a damaging effect on durability. Such situations are likely to occur in cold weather at the time of removal of formwork.