Hot, dry, or windy days create myriad challenges for concrete. The hydration reaction that gives concrete its strength happens faster in hot weather, so that means your batch will quickly lose its slump and become hard to place and finish.
Water the concrete needs for this the reaction evaporates quickly as the batch heats up. That means a higher likelihood of plastic shrinkage cracking—fine cracks that develop before you can start troweling. Concrete’s chemical reaction also produces heat that causes the slab to expand, but then it contracts as it cools, which causes more cracks.
The temptation is to add water on site to keep the batch workable. But extra water weakens the concrete, causing more cracks and jeopardizing the strength and hardness of your slab.
One solution is to ask your batch plant for a good hot weather mix with chilled water and helpful admixtures to moderate chemical heating. Also, get extra help for the pour, and provide shade where you’re working or schedule the pour when the sun angle is low and there’s natural shade. Finally, cure the concrete carefully with a curing compound or a continuous water bath.