What is cold weather? Generally we define cold weather as a period when the average daily temperatures fall below 40 degrees F for more than three days in a row. These conditions require special precautions when placing, finishing, curing and protecting concrete from the effects of cold weather. Good construction practices and proper planning are important.

Tips for protecting concrete in cold weather:

1. Check with your ready mix producer to discuss heating water or aggregates, increasing cement content, or adding an accelerating admixture.
2. Use air entrainment if concrete is exposed to freezing during construction and for all exterior flatwork.
3. Provide a warm subgrade, reinforcing and forms; don’t place concrete on frozen subgrade.
4. Provide sufficient insulation blankets or heaters.
5. Cover the concrete with the insulation blankets to conserve the internal heat generated by the concrete; provide triple insulation at corners and edges.
6. Use heated enclosures to block wind, keep out cold air and conserve heat.
7. During the first 24 hours, carbon dioxide produced by unvented combustion heaters can cause soft, dusting floors. Make sure the carbon dioxide is vented outside the enclosure.
8. Gradually cool the concrete; a maximum of 50 degree F drop in 24 hours is OK.

What happens to concrete in cold weather? Freezing Temperatures freeze the mix water, reducing the concrete strength up to 50%. Protect against freezing until it reaches 500 psi compressive strength. Concrete should be placed and maintained at a temperature above 50 degrees F by insulating or heating it for three days. As cold weather slows concrete strength gain, increase concrete set time up to one-third for each 10 degree F decrease in air temperature. If multiple freeze-thaw cycles are expected, protection should be provided until the concrete reachs 3500 psi compressive strength. One hundred pounds of extra cement or the use of an accelerator will provide high-early-strength to reduce protection periods by about one-third. Use of less water will counter-act delays in set time and allow increased strengths for resistance to freeze-thaw action. Curing of the concrete surface should not be done with water; a membrane curing system or impervious paper or plastic sheets will provide the best cold weather curing.