ACI 305R
Guide to Hot Weather Concreting
Placing concrete when high temperature, low humidity, wind, and solar radiation combine to work against a successful placement.
Who needs it
Contractors and ready-mix suppliers working through summer, inspectors, and specifiers writing hot-weather provisions into a project.
What the test involves
It explains why hot conditions accelerate slump loss and setting, shorten finishing time, increase water demand, and raise the risk of plastic shrinkage cracking and reduced long-term strength. It then covers countermeasures: cooling the ingredients or the mix, adjusting admixtures, scheduling placements for cooler hours, pre-wetting subgrade and forms, shading and windbreaks, and beginning curing immediately rather than after finishing is complete. The controlling variable is usually the rate of evaporation from the fresh surface, not the air temperature by itself.
Common misconceptions
- Hot weather is not just an air-temperature problem. Wind and low humidity can make a mild day more dangerous to a slab than a hot, still, humid one.
- Adding water to restore workability lost to heat is the single most damaging response, because it trades a short-term finishing convenience for permanent strength and durability loss.
- Concrete placed hot can gain early strength faster and still end up weaker at the specified test age than the same mix placed cool.
Official source
We summarize scope and purpose only. The full text belongs to the issuing body — read it at the official source. American Concrete Institute