Under what circumstances should a concrete mix be rejected?

A concrete mix should be rejected if it fails to meet strength and consistency specifications because these factors are critical to ensuring the durability, performance, and safety of the finished structure. Strength specifications indicate the load-bearing capacity, which is essential for the structure to perform its intended function without risk of failure. Consistency, which pertains to workability, also plays a significant role in the mix’s ability to be placed and finished properly. If the mix cannot achieve the required strength or the necessary level of consistency, it poses a risk to the structural integrity and overall quality of the concrete.

While the other options may raise concerns, they do not directly correlate with fundamental structural safety and performance requirements. A mix could theoretically meet the strength specifications despite being mixed for over an hour or having color inconsistencies—for instance, if it maintains the appropriate mechanical properties. However, if the mix does not conform to the established standards for both strength and consistency, it undermines the reliability of the construction project and should therefore be rejected.