Concrete pours can be performed and completed even during the coldest temperatures, as long as the right measures are taken to ensure a quality concrete product. The goal is to make sure that the concrete is poured at the correct temperature, and the concrete is able to reach strength without early age freeze damage.
Why are Cold Weather Concrete Practices & Precautions so Important?
Weather plays a major role in concrete construction due to the chemical reaction known as hydration. When new concrete cools down due to cold weather, hydration slows down. If hydration slows down too much, the crystals in the chemical reaction do not properly form, and the concrete will not reach strength. Once the concrete has reached a strength of 500psi it can combat freezing temperatures. In order to reach 500psi, the concrete needs to be kept at or above 50 degrees Fahrenheit for 48 hours.
What Specifically is Cold Weather Concreting?
According to the ACI Committee, “cold weather exists when the air temperature has fallen to or is expected to fall below 40 degrees Fahrenheit during the protection period. The protection period is defined as the time required to prevent concrete from being affected by exposure to 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 ||55℉ [13℃]|
|12 – 36 [300 – 900]||50℉ [10℃]|
|36 – 72 [900 – 1800]||45℉ [7℃]|
What Methods Aid in Pouring Concrete in Cold Weather?
- Concrete Mix Acceleration – This includes accelerating chemical admixtures, decreasing water content, increasing cement percentage, changing pozzolan quantity, and replacing Type 1 cement with Type 3 cement. All of the above methods will aid your concrete in setting up faster.
- Insulation / Heat Systems / Enclosures – This includes enclosing the area around the concrete pour with visqueen and applying heaters to keep the concrete from freezing.
- Never pour concrete on frozen ground – If necessary, use a heat source to thaw out frozen ground prior to pouring concrete.
- Air Entrained Concrete – Make sure that exterior concrete is air entrained for freeze thaw cycles.
- Curing Blankets – After finishing concrete, cover it with curing blankets. Curing blankets will keep the concrete from freezing.