ACI 306R
Guide to Cold Weather Concreting
Placing and protecting concrete when low temperatures slow strength gain and freezing threatens to destroy fresh concrete outright.
Who needs it
Contractors and ready-mix suppliers working through winter, inspectors, and specifiers writing cold-weather protection into a project.
What the test involves
It defines cold-weather conditions in terms of low average daily temperature sustained over consecutive days, rather than a single cold night, and sets out the protection period concrete needs before it can safely be exposed. Measures include heating mix water or aggregates, using accelerating admixtures or higher early-strength cements, insulating blankets and heated enclosures, protecting corners and edges that lose heat fastest, and controlling how quickly protection is removed so the concrete is not thermally shocked. Freezing before the concrete has developed enough strength causes permanent, unrepairable damage.
Common misconceptions
- Concrete does not stop curing in the cold — it slows down dramatically, which means forms stay up longer and strength milestones arrive later than the schedule assumed.
- Antifreeze admixtures do not prevent freezing in the way the name suggests. Accelerators shorten the vulnerable window; they do not remove the need for protection.
- Pulling blankets off on a sunny afternoon can crack a slab through thermal shock, so how protection ends matters as much as that it was used.
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