There's no single cut-off, but below 5°C you need cold-weather measures. With protection, concrete can be placed in freezing weather.
Cold-Weather Concreting.
Concrete can be placed in winter, but it must not freeze while it's young. Protect it until it gains enough strength to resist frost.
At a glance:
Below 5°C : When cold-weather measures apply
3.5 MPa : Strength before exposure to freezing
10°C+ : Target concrete temperature while curing
Why Cold Weather Is a Risk.
Low temperatures slow hydration, so concrete sets and gains strength slowly. If water in fresh concrete freezes, it expands and can permanently damage the concrete. One early freeze can cut its strength significantly.
Protecting New Concrete.
Cover concrete with insulated curing blankets as soon as finishing allows. Keep it protected until it reaches at least 3.5 MPa, usually several days in cold conditions.
If you use heaters inside an enclosure, vent fuel-fired units outside. Exhaust can damage the fresh surface. Remove protection gradually to avoid thermal shock.
Before the Pour:
Never pour on frozen ground: Thaw and protect the subgrade first. Remove snow and ice from forms and reinforcing.
Ask for heated concrete: We can supply concrete batched with heated water.
Consider an accelerator: It speeds up setting and early strength gain.
Line up protection: Have insulated blankets, enclosures or heaters on site before the truck arrives.
Frequently Asked Questions
What's the lowest temperature I can pour at?
Does antifreeze exist for concrete?
Not in the way people think. Accelerators and heated water help concrete set faster, but it still needs protection.
How long do blankets need to stay on?
Until the concrete reaches at least 3.5 MPa. In cold weather, that can take several days.
Should exterior winter slabs have air entrainment?
Yes. Air entrainment protects against freeze-thaw cycles for the life of the slab.
Does winter concrete cost more?
Heated water, accelerators and protection add cost. [Dolans CONFIRM winter surcharge]
Disclaimer: These guides are general information. Always follow your engineer's specification and local building requirements.
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