What is the maximum allowable temperature for freshly mixed concrete according to ACI recommendations?

The maximum allowable temperature for freshly mixed concrete, according to ACI (American Concrete Institute) recommendations, is indeed set at 90°F (32°C). This limit is established to ensure the proper curing and hydration of the concrete. When concrete is mixed and placed at higher temperatures, it can lead to accelerated setting times, which may result in incomplete hydration of the cement particles. This incomplete hydration compromises the strength and durability of the concrete.

High temperatures can also trigger problems such as thermal cracking and may negatively affect the uniformity of the mix. By adhering to the 90°F limit, particularly in hot weather conditions, procedures can be implemented to mitigate these risks—such as using cooler mixing water, shading the mix, or adjusting materials to maintain optimal performance.

Following this guideline helps ensure that the concrete can achieve its intended mechanical properties and longevity in its service environment. It also promotes best practices for quality control in concrete placement and handling.