What Is Cold Weather Concreting?
Cold weather concreting is the set of practices in ACI 306R for placing concrete when air temperatures fall below 40°F — protecting the fresh concrete from freezing before it gains strength and ensuring it cures properly in the cold. Concrete that freezes before reaching ~500 psi is permanently damaged. Cold-weather placement is routine with proper planning; it is a disaster without it.
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Why cold damages fresh concrete
Water expands when it freezes — ice formation in fresh concrete disrupts the hydrating paste, destroying up to 50% of the potential strength with a single early freeze. Even without freezing, cold slows hydration dramatically: concrete placed at 35°F gains strength at a fraction of the warm-weather rate, delaying form removal, shoring release, and loading. The protection period extends until the concrete reaches the specified strength.
Required practices
Heat the water and aggregates (never let cement contact water above 175°F), use accelerating admixtures or Type III cement where appropriate, place on thawed subgrade (never on frozen ground — it settles when it thaws), and protect the placed concrete with insulated blankets or heated enclosures. Maintain the concrete above 55°F (or the specified minimum) for the protection period — typically 3-7 days depending on the element and exposure. Monitor with maturity meters or field-cured cylinders.
Planning and cost
Cold-weather concreting adds 10-30% to the concrete scope: heating, enclosures, blankets, admixtures, extended protection labor, and slower strength gain delaying the schedule. Plan the winter pours in the project schedule rather than discovering the requirements at the batch plant. The special inspector verifies protection measures and temperature records — unprotected cold-weather concrete gets cored and tested, and rejected if it froze.
The bottom line
Cold-weather concreting per ACI 306R: heat materials, place on thawed subgrade, protect above 55°F until strength develops, and monitor with maturity meters. Budget 10-30% extra for winter placement.
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