What Is Hot Weather Concreting?
Hot weather concreting is the set of practices in ACI 305R for placing concrete when heat, wind, and low humidity threaten the pour — accelerating set, increasing water demand, and driving plastic shrinkage cracking. Concrete placed above ~90°F without precautions sets too fast to finish properly and loses long-term strength and durability. Summer placement is routine with planning; it fails without it.
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How heat damages concrete
High concrete temperatures accelerate hydration — the mix stiffens before the crew can place and finish it, creating cold joints and poor consolidation. Hot concrete needs more water for the same workability, and that extra water (if added) weakens the concrete permanently. Rapid surface drying drives plastic shrinkage cracking within hours. The durability penalty of hot-weather placement without precautions shows up years later as scaling and cracking.
Required practices
Cool the ingredients (chilled water, shaded aggregates, liquid nitrogen for mass placements), schedule pours for early morning or night, use retarding admixtures to extend the finishing window, protect the fresh surface with evaporation retarders and windbreaks, and start curing immediately — water curing or curing compounds before the surface dries. Limit the concrete temperature at placement (typically 95°F maximum per ACI 305). Have backup plans: a retarder dose, extra crew, and a tested contingency for equipment breakdowns.
Planning and inspection
Hot-weather concreting plans belong in the pre-pour meeting: temperature limits, admixture strategy, crew sizing for the accelerated schedule, and curing resources staged before the trucks arrive. The special inspector monitors concrete temperature at placement and verifies curing. Concrete that sets before it is consolidated is defective — there is no repair for a cold joint through a structural member.
The bottom line
Hot-weather concreting per ACI 305R: cool ingredients, pour early, retard the set, protect from evaporation, and cure immediately. Keep placement temperature under 95°F and stage the curing before the trucks arrive.
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