10.12 : 寒い天候でのコンクリート打設

During cold weather, when freshly placed concrete starts to freeze before it sets, the water in the concrete converts to ice, resulting in its expansion.

Water in ice form is unavailable for cement hydration, during thawing, it melts into water, which aids in cement hydration.

Consequently, the concrete hardens in its expanded state, resulting in larger void volumes and weakening the concrete.

Similarly, expansion upon freezing of set concrete before it gains strength leads to its disruption.

Concrete is prepared using aggregates heated using steam or water if the ambient temperature is below 40°F.

Furthermore, using Type III cement, accelerators, and air-entraining admixture in concrete is ideal for cold-weather concreting.

Concrete is placed in formwork made of insulating material, and the surfaces receiving concrete should be free of snow.

After placing concrete, it is covered with blankets for a sufficient duration, or sometimes, shelters are built around it, and heat sources are added inside to protect the concrete from cold conditions.

Lastly, the temperature of the concrete is monitored using thermocouples installed in the concrete to ensure proper thermal insulation.