Due to the chemical reactions of hydration, weather plays an important role in concrete construction. When new concrete cools down due to cold weather, the hydration process slows down. If the hydration rate slows down too slowly, the crystals in the chemical reaction cannot form normally, and the concrete cannot reach its strength. Once the strength of concrete reaches 500 pounds per square inch, it can withstand severe cold. To achieve 500psi, concrete needs to be maintained at a temperature of 50 degrees Fahrenheit or above for 48 hours.
What is concrete in cold weather?
The ACI Committee points out that during the protection period, cold weather occurs when the temperature drops or is expected to drop below 40 degrees Fahrenheit. The definition of protection period is the time required to prevent concrete from being affected by cold weather。
Cold Weather Concrete Temperature Requirements:
ASTM C94 goes into depth on the temperatures in which concrete is to be poured during cold weather. The chart below breaks this down based on the thickness of the concrete slab.
| Section Size, minimum dimension, inch [mm] | Concrete temperature as placed |
|---|---|
| less than 12 [300] | 55℉ [13℃] |
| 12 – 36 [300 – 900] | 50℉ [10℃] |
| 36 – 72 [900 – 1800] | 45℉ [7℃] |
What are the methods of pouring concrete in cold weather?
Accelerate concrete mixing - This includes accelerating chemical admixtures, reducing water content, increasing cement percentage, changing the content of volcanic ash, and replacing type 1 cement with type 3 cement. All of the above methods will help your concrete solidify faster.
Insulation/Heating System/Shell - This includes sealing the surrounding area of concrete pouring with goggles and using heaters to prevent concrete from freezing.
Do not pour concrete on frozen soil - if necessary, use a heat source to thaw the frozen soil before pouring concrete.
Aerated concrete - Ensure that the external concrete is aerated through freeze-thaw cycles.
Curing blanket - After the concrete pouring is completed, cover it with a curing blanket. A solidified blanket can prevent concrete from freezing.
