Working with Concrete in Cold Weather

On Colorado's Western Slope, the construction season doesn't stop when temperatures drop. With proper planning and the right materials, successful concrete pours are possible even in cold weather. Here's what every contractor and homeowner should know about cold-weather concreting.

When Is It "Cold Weather" Concreting?

The American Concrete Institute (ACI 306) defines cold weather concreting as any time the air temperature has been or is expected to fall below 40°F during the protection period. At these temperatures, concrete hydration slows dramatically, and fresh concrete can freeze if not properly protected — leading to permanent strength loss of up to 50%.

Keys to a Successful Cold-Weather Pour

• Use hot water in the mix to raise the initial concrete temperature to at least 50°F
• Request accelerating admixtures from your ready-mix supplier to speed up set time
• Never place concrete on frozen ground — thaw the subgrade first
• Protect fresh concrete with insulating blankets for at least 48 hours
• Monitor concrete temperature during the curing period
• Avoid using calcium chloride accelerator with embedded metals

Protecting Fresh Concrete

Insulating blankets are the most common protection method for flatwork. They trap the heat generated by the hydration process to keep the concrete warm. For walls, columns, and other formed work, heated enclosures may be necessary. The concrete should maintain a temperature of at least 50°F for the first 48 hours and should not be allowed to freeze for at least the first 7 days.

If you're using concrete blankets, make sure edges are weighted down or secured to prevent wind from getting underneath. Wind chill can dramatically reduce the effectiveness of insulating blankets.

Rebar Placement in Cold Weather

Rebar placement during cold weather requires extra attention. Frozen ground can shift during thaw cycles, potentially displacing rebar before the pour. Ensure your subgrade is properly compacted and completely thawed before placing reinforcement. Also verify that rebar is free of ice, snow, and frost before pouring — these can create voids and weaken the bond between steel and concrete.

We Stock What You Need

Rocky Mountain Building Solutions stocks concrete accessories, forming materials, rebar, and insulating blankets to support your cold-weather concrete work. Our team has years of experience advising contractors on successful winter pours. Contact our Delta or Montrose locations for product availability and expert guidance.