What is Cold-Weather Concreting?

Have you ever noticed that the 3500 psi concrete mix that performed so marvelously back in the summer and fall is performing lousy during these cold winter months? It looks dead, takes forever to place and finish, and the compressive strength values are disgustingly low. What’s the matter with this wintertime concrete? Well, it’s winter and cold; that’s the major problem!

Like us, concrete is warm-blooded; it doesn’t like cold weather. It wants to be kept warm and must be kept warm to reach its potential. The American Concrete Institute (ACI) defines cold weather concreting as a period when the average daily ambient temperature is below (or expected to fall below) 40 °F for more than three consecutive days. Low, cold temperatures (especially freezing) can significantly slow down the hydration process of cement, thus greatly affecting the strength development process. Freezing temperatures within the first 24 hours (when concrete is still in the plastic state) can reduce the strength by 50% or more.

Keep concrete warm and place it at temperatures per Table 5.1 of ACI 306R (around 50 °F to 60 °F), pictured above. Maintain the proper concrete protection period temperatures according to the related ACI 306R, Table 7.2, and the concrete will develop the proper strength and required durability qualities.

ACI 306R, Section 2 - Definition of Cold Weather: ACI 306R, Section 2 - Definition of Cold Weather: “Cold weather - When air temperature has fallen or is expected to fall below, 40 F during the protection period; protection period is defined as the time recommended to prevent concrete from being adversely affected by exposure to cold weather during construction.” (See ACI 306R, Chapter 7, Table 7.2 for protection period.)

For more information or further enthusiastic discourse on topics of CODE, please contact Alan Tuck at: [email protected] or 540.344.7939.