Anyone who has previously worked in construction is aware that optimum weather conditions are rarely present. If you waited for the perfect day to get to work, you’d only pour concrete a handful of days per year.
The American Concrete Institute explains, “…one or a combination of the following conditions that tend to impair the quality of freshly mixed or hardened concrete by accelerating the rate of moisture loss and rate of cement hydration, or otherwise causing detrimental results: high ambient temperature; high concrete temperature; low relative humidity; and high wind speed.”
Concrete can adequately set in anywhere between 8 and 48 hours in good weather. Although it can set adequately in a week’s time, it takes up to a month to cure completely.
Although many contractors may find working with concrete to be second nature, it can be a tricky material to work with due to how quickly it can change when exposed to various temperatures, humidity levels, and wind speeds.
How Does Heat Affect Concrete?
Concrete that is poured during hot weather conditions is more likely to develop cracks since moisture evaporates quickly in the heat. If concrete is laid in a place where the temperature is high during the day but drops significantly at night, it will also be more prone to cracks.
Due to these factors, concrete that is mixed and allowed to cure at 75° F will probably perform better than concrete that is mixed and allowed to cure in 100° F weather. Simply said, while dealing with concrete in warm weather, timing and prior knowledge are vitally essential.
Concrete should ideally be worked with or poured while the temperature is between 50 and 60 degrees Fahrenheit. However, contractors are advised to aim to keep the maximum concrete temperature at 95° F according to the ACI guidelines for setting and mixing concrete in hot weather. Concrete can adequately set in anywhere between 8 and 48 hours in optimal weather.
What About Cold Weather?
The ACI defines cold weather as three consecutive days of low temperatures, specifically those below 40° F. The ACI also defines “cold weather” as air temperatures that remain below 50° F for more than 12 hours at a stretch. Newly poured concrete and cold weather do not play well together.
When water and concrete powder are combined, a chemical reaction takes place right away that causes the concrete to crystallize internally. Concrete can endure additional pressure that might be brought on by frozen water molecules in the concrete, thanks to these crystals. Even in frigid conditions, crystals will continue to grow for a long time. Low temperatures, on the other hand, will stop them from growing and prevent the concrete from curing to its maximum compressive strength.
The golden rule for contractors is to never pour concrete straight onto ground that has frozen or thawed when working in cold weather. In fact, once the ground thaws, it will settle. Because of this, pouring concrete in extremely cold weather may also be prone to cracking.