Hot weather concreting precautions

Hot weather (ambient temperature above 40 °C, or high temperature with low humidity and wind; IS 7861 Part 1, referred to by IS 456 cl. 14.1, and ACI 305) speeds up setting, reduces slump, increases water demand and causes plastic shrinkage cracking. The concrete temperature at placing should preferably be kept below about 35 °C, and IS 7861 does not allow it above 40 °C.

Precautions

1. Materials: keep aggregates in the shade and sprinkle them with water; use chilled water or crushed ice as part of the mixing water; shade water tanks and pipes and paint them white; do not use cement that is still hot from the silo.
2. Mix: use a low-heat cement or PPC, a lower cement content, and a retarder or water-reducing retarder admixture; keep the w/c fixed and do not add water to regain slump.
3. Transport and placing: shorten the time between mixing and placing; cover mixers, ready-mix trucks and pump lines; place at night or early in the morning; avoid delays and cold joints.
4. Forms and subgrade: wet the formwork, reinforcement and subgrade before placing (with no standing water); shade the work with sunshades.
5. Protection and curing: start curing immediately; use fog sprays, evaporation retarders, wet hessian, plastic sheeting or a curing compound; cure continuously for at least 10 days (IS 456 cl. 13.5.1 for hot, dry weather); protect from wind to prevent plastic shrinkage cracks.
6. Provide additional joints and thermal control in thick sections.