What percentage of particles retained on the 19mm sieve is the threshold for Test Method C?

The correct answer is 30%, which serves as the threshold for Test Method C regarding the percentage of particles retained on the 19mm sieve. In this context, Test Method C is used to determine the suitability of aggregate base materials, particularly focusing on the maximum allowable amount of coarser particles that can be retained on a specific sieve.

This threshold is set to ensure that the aggregate meets the specifications needed for effective performance in construction applications. If the amount of material retained exceeds this limit, it may indicate that the aggregate is too coarse, potentially leading to performance issues such as insufficient compaction or inadequate load distribution.

The other options, while they represent percentage values, do not meet the specific criteria established in Test Method C. Thus, the guideline of using 30% as the cutoff is critical for maintaining material quality in aggregate applications, contributing to the longevity and stability of the constructed infrastructure.