Hot weather concreting
Placing concrete under conditions of heat, sun, wind, or low humidity that accelerate slump loss and setting and raise the risk of cracking and reduced strength.
What does hot weather concreting mean?
Heat shortens the finishing window dramatically and increases water demand, tempting crews into the one response that permanently damages the concrete. Standard countermeasures include cooling mix water with ice, scheduling placements for early morning, pre-wetting subgrade and forms, erecting windbreaks and shade, using retarders, and starting curing immediately. Concrete placed hot gains early strength faster and typically ends up weaker at the test age.
In practice
Summer residential pours often start before sunrise for exactly this reason, and the crews that do it have noticeably fewer callbacks.