There is no single "too cold" air temperature. Cold-weather concrete practice starts around 40 F, and fresh concrete itself freezes if it falls below about 25 F. Frozen fresh concrete can lose more than half its potential strength, so it has to be protected until it reaches 500 psi, about two days after placement. Pouring in cold is possible with the right protection. Pouring and walking away is not.
What temp to pour concrete in winter? Two numbers matter, and people mix them up. Cold-weather practice begins around 40 F. Fresh concrete freezes if its own temperature falls below about 25 F (NRMCA). Between those two, you can pour, but only with a plan.
The number that ruins concrete: about 25 F
Fresh concrete freezes if its temperature falls below about 25 F. Frozen fresh concrete can lose more than 50 percent of its potential strength and will not be durable (NRMCA). That loss is the reason winter pours get protected, not a reason to refuse every winter pour.
The key word is "fresh." Once the concrete reaches 500 psi, which NRMCA puts at about two days after placement, it is past the worst of the freezing risk (NRMCA). Protecting it until then is the job. NRMCA also says to protect it from freeze-thaw cycling while wet until it reaches at least 3500 psi (NRMCA).
The number where cold-weather rules start: about 40 F
This is where we need to be careful, because the definition depends on the edition you use. NRMCA's older wording defines cold weather as more than 3 consecutive days with an average daily temperature under 40 F and air temperature not above 50 F for more than half of any 24 hour period. Since ACI 306R-10, cold-weather provisions apply when the air temperature is below, or expected to fall below, 40 F during the protection period. The newer definition triggers cold-weather practice more often, and which edition governs depends on the code adopted (NRMCA). We got the newer wording from a secondary source, so treat it as a guide and ask what your project follows.
The practical point: "above freezing" is not safe. A pour at 35 F with a cold night coming needs the same planning as one at 30 F.
What changes the answer
Air temperature alone does not tell you whether a pour will work.
- The base. Snow, ice and frost must be removed before placing, and the surfaces touching the concrete must be above freezing. No concrete should go on a frozen subgrade (NRMCA, NRMCA).
- How warm the concrete arrives. NRMCA recommends 55 F as placed for sections thinner than 12 inches (NRMCA).
- How fast it cools. Do not let it cool faster than 5 F per hour for the first 24 hours (NRMCA).
- Curing. When freezing is expected, use moisture-retaining curing, not wet curing (NRMCA).
- Accelerators. They speed setting but do not prevent freezing (NRMCA).
For how crews actually do this, see how concrete gets poured in a Chicago winter. For when you can step or drive on it afterward, see how long before you can walk or drive on new concrete.
So should you pour?
If the forecast is near or below freezing and the contractor has no protection plan, wait. If they can name the delivery temperature, how they will cover and insulate the slab, and how long, a winter pour can work. Our concrete team will tell you straight when to wait. The concrete guide has more.
Common questions
Cold-weather practice already applies near 40 F, and fresh concrete freezes below about 25 F. At 32 F a pour is possible only with a plan: warm concrete, a frost-free base, and covering until the slab reaches 500 psi, about two days.
No. Accelerators speed setting but do not prevent freezing. Calcium chloride should not exceed 2 percent by weight of cement, and a non-chloride product is advised where steel corrosion is a concern.
Sources
- National Ready Mixed Concrete Association: Concrete in Practice 27: Cold Weather Concreting (PDF)
- National Ready Mixed Concrete Association: Concrete in Practice 11: Curing In-Place Concrete (PDF)
- National Ready Mixed Concrete Association: Concrete in Practice 4: Cracking Concrete Surfaces (PDF)
Facts last checked: October 7, 2026.
This article explains general rules and common situations in Chicago. It is not legal advice, and City rules change. For a specific property, check with the Chicago Department of Buildings or a licensed professional.