So you’re prepared and you’ve got the right mix, now what? For flatwork, the traditional, and still the best way, to protect concrete from the cold is to cover it with blankets after it’s been finished. Since the ground is a bit warmer and the concrete generates its own heat, blankets will keep it warm even if the temperature goes below 20°F. A few things to think about are:
- Remember the definition: If the air is below or expected to go below 40°F, then use cold weather techniques.
- When finishing concrete in cold weather, you still need to wait for all the bleed water to evaporate. Bleed water is basically the concrete particles settling (like mud in a stirred up pond) and squeezing out all the extra water. If you finish that water into the surface, you increase the water-cement ratio and get weak surface concrete. Since the concrete is setting more slowly in the cold, bleeding starts later, lasts longer, and you can get more bleed water. You can try getting it off with squeegees or vacuums–or you can wait.
- Typically, you only need to keep the blankets on for a couple of days, if the concrete is warmer than 50°F.