Cold Weather Concreting:
During hydration process temperature plays a great role on the rate of strength development. When the temperature is just above the freezing point the rate of hydration becomes very slow. The hydration that occurs in 1 day at a temperature of 20°C may take up to 7 days at 4°C temperature. Thus the time for removing formwork also extends. So some precautions should be taken while concreting in cold weather.
Precautions For Cold Weather Concreting:
1. Hot water (60°C) and aggregates (15°C) should be mixed before adding cement content in the mix.
2. Concrete should be placed at a temperature of 4° -5° C. After placing and compacting the temperature should be kept at 2°C until it becomes hardened.
3. To prevent flashing, cement should not be added alone with water.
4. Do not use frozen aggregates in the mix.
5. Accelerating admixtures (mainly calcium chloride) can be used to increase the internal temperature of concrete.
6. Damaged concrete due to frost action should be eliminated.
7. Formwork should be cleaned and free of snow or ice.
8. To keep the temperature at constant and to protect the concrete from frost action, the concrete surface should be covered with dry blankets of cement bags, staws, tarpaulins etc.
9. Curing should be extended for a longer period.
10. Formwork should be removed after a longer period.