High air temperature during concreting, sometimes aggravated by the effects of wind or low relative humidity or both, can impair the quality of the concrete. Improvised responses to the unexpected seldom succeed, and the damage that the hot weather causes can never be completely alleviated. Immediate effects on fresh concrete can be more water demand for the same slump or workability, greater slump loss, faster setting, more likelihood of plastic cracking, and more difficulty in controlling the air content. After hardening, the concrete may have lower strength, more drying shrinkage and tendency to crack, less durability in freeze-thaw exposures, and less uniform surface appearance.
All of these effects can be virtually overcome by careful selection of materials and procedures for hot weather work, with the key being advance planning. Areas which have special requirements for a successful, well-run hot weather job include planning, concrete production, delivery and discharge, placing and finishing, curing and protection, and testing and inspection, where required.
For example, materials should be batched and mixed at the site, possibly using a jobsite plant, if the project is large enough. Water should not be added to ready mixed concrete at the job site unless it is part of the amount required initially for the specified maximum water-cement ratio and the specified slump. On some jobs contractors may find that they themselves can exercise best control in this regard.