In the Mix with Cemstone’s Business Development Engineers
John Lee, P.E. & Jim Grothaus, P.E.
December 19, 2023
Like it or not, the cold temps are back🥶Whether you’re a Midwesterner through and through or a newbie in town, it’s good to know what’s up when working with concrete in chilly conditions.
What is cold weather concrete?
Cold weather concreting occurs when the air temperature is or is anticipated to drop below 40°F during the recommended cold weather protection period, aiming to prevent negative impacts on concrete due to exposure to cold weather during construction, as outlined in the American Concrete Institute (ACI) 306R-16, “Guide to Cold Weather Concreting.”
So, are there benefits and objectives to a cold weather concrete protection plan? Yes! Below are some key elements that should be included:
• Prevent damage to concrete due to early-age freezing. Concrete can withstand a single cycle of freezing when it has obtained a compressive strength of 500 psi in a dry condition. At 50°F, most well-proportioned concrete mixtures reach this strength within 48 hours.
• Ensure that the concrete develops the required strength for safe removal of formwork and for safe loading of the structure.
• Maintain curing conditions without using water curing. During cold weather, water curing may reduce the resistance to freezing and thawing when protection is removed.
• Limit rapid temperature changes, particularly before the concrete has developed sufficient strength to withstand induced thermal stresses. Rapid cooling of concrete surfaces or large temperature differences between the exterior and interior can cause cracking and reduce the strength or durability of the concrete member.
• Provide protection consistent with the durability of the structure during its design life. Surfaces and corners must be protected from freezing, dehydration, and cracking from overheating due to inadequate protection, improper curing, or careless workmanship.
Who should develop the cold weather concrete protection plan?
A cold weather plan is a team effort between your ready-mix supplier and the contractor. Each has responsibilities for executing the plan. The following should be considered:
- All formwork and subgrade should be free and clear of snow and ice. The temperature difference of the subgrade and fresh concrete should not be greater than 20°F.
- When temperatures are below 10°F, metallic embeds should be warmed prior to placement. Embeds with a cross-section 4 in2 or greater should be warmed to at least 32°F. A heated enclosure or insulated concrete curing blankets may need to be used before the concrete is placed.
- The air temperature on the placement day must be determined. Table 1 of Cemstone’s Cold Weather Protections Plan provides recommended concrete temperatures, based on the air temperature and member size.
- Concrete placed in cold weather conditions must be protected using a heated enclosure or insulating blankets. Table 2 of Cemstone’s Cold Weather Protections Plan provides the recommended length of the protection period based on the use and exposure condition of the concrete member.