What is the minimum number of revolutions required when using a truck mixer?

The correct answer is based on industry standards that dictate the necessary amount of mixing to ensure uniformity and proper hydration of the concrete mix. The minimum number of revolutions for a truck mixer is typically specified to be a minimum of 70 revolutions once the materials have been combined in the drum.

This standard ensures that the concrete achieves the desired consistency and homogeneity, which is crucial for the structural integrity of the finished product. Insufficient mixing can lead to variations in strength and performance due to uneven distribution of the cement, water, and aggregates.

When considering the other options, they either fall below or above the established standards for effective mixing. Choosing a number less than 70 would not meet the minimum requirements and could compromise the quality of the concrete being delivered. On the other hand, while 80, for instance, could deliver adequate mixing, it exceeds the minimum requirement and may not be necessary for every mix, thereby being less efficient. Hence, 70 revolutions is the optimal answer that aligns with established best practices in concrete mixing.