How Is Concrete Protected During Hot-Weather Placement?

Hot-weather concreting per ACI 305 limits the concrete temperature as delivered and placed — commonly targeting below 95°F at placement — using cooled mix ingredients, scheduling, shading, and admixtures. Evaporation control (fogging, retardants, windbreaks) prevents plastic shrinkage cracking, and prompt curing must start the moment finishing allows. Heat attacks concrete on two fronts: it accelerates the chemistry, collapsing the window for placing and finishing, and it drives evaporation that cracks the surface before the concrete has any strength. The hot-weather plan manages both — the mix's internal temperature and the surface's exposure — because fixing either one alone still leaves the pour vulnerable.

Cooling the mix is the first lever: chilled water, ice as partial mix water, shaded aggregates, and night batching all lower the delivery temperature. Every 10 degrees of concrete temperature changes set time noticeably, so cooling buys working time directly. Scheduling is the second lever — placing at night or dawn dodges the worst heat, and sequencing large placements so each section is finished before the next arrives prevents cold joints. Surface protection is the third lever and the one most often skipped. Evaporation retardants sprayed after screeding, fogging that raises humidity without adding mix water, and windbreaks around the placement all slow surface drying. Then curing has to start immediately — in hot weather the window between finishing and surface drying can be minutes, not hours, and curing compound or wet coverings need to be staged and ready before the pour begins.

Hot-weather success is decided before the trucks roll. The pre-pour checklist:

• Set a maximum placement temperature in the spec and enforce it at the truck: reject loads that arrive too hot
• Schedule large placements for night or early morning: the cheapest cooling is avoiding the heat
• Stage evaporation control before the pour: retardant, fogging equipment, and windbreaks ready at the deck
• Prohibit jobsite water additions beyond the mix allowance: protect the water-cement ratio
• Start curing the moment finishing allows: in heat and wind, the curing window is measured in minutes