ACI 306 defines cold weather concreting as a period when the average daily air temperature is less than which of the following?

The definition of cold weather concreting according to ACI 306 specifies that it occurs when the average daily air temperature is less than 40°F. This standard is important for construction practices, as it addresses the effects of cold temperatures on the setting and curing of concrete. Concrete is sensitive to temperature changes; when the temperature drops below this threshold, it can adversely affect the hydration process, leading to potential issues such as insufficient strength development, cracking, or difficulty in placing and finishing the concrete.

Maintaining proper temperature conditions during the curing process is crucial for ensuring that the concrete reaches its intended strength and durability. Understanding this definition helps contractors take necessary precautions, such as using insulation, heating methods, or special admixtures to ensure successful concrete performance during cold weather conditions.