Can your concrete stand up to the weather? The Iowa Department of Natural Resources’ senior AFO engineer Paul Petitti is a professional when it comes to concrete inspections.
“Concrete contains water and must not be allowed to freeze in the first seven days,” he says. “If properly cured, the concrete will reach about 70 percent of its design strength in the first week. And, about 90 percent of its design strength in 28 days.”
Follow Petitti’s tips for cold weather concrete to be successful.
Plan ahead, look at long-term forecasts and suspend concrete pouring for the season once cold weather hits.
When construction can’t be halted, follow these practices once temperature drops below freezing:
- Use insulating blankets to keep ground from freezing before you pour a floor slab and to cover the floor slab after pouring. Leave blankets on for seven days.
- Use insulating blankets to keep freshly poured walls from freezing. Leave blankets and forms on for three days. If temperatures remain below freezing, replace blankets and leave in place for four more days.
- If cold weather arrives after properly pouring slabs and walls and the pit’s been backfilled, put a few feet of water into the deep pit to prevent frost heave.
Be aware:
- Hot water in the concrete mix can help, but it is not a substitute for blankets.
- An accelerator admixture in the concrete (calcium chloride) may also help, but, again, it is not a substitute for blankets.
- Plastic drain tile becomes very brittle in cold weather, so it is subject to breaking during construction activities such as backfilling.
Petitti reminds contractors they must call and notify the regional DNR field office before pouring slabs.
DNR rules refer to the American Concrete Institute’s Standard 306 "Recommended practices for Cold Weather Concreting.” Refer to the 306 Standard for a thorough understanding of cold weather concreting.