When should Method B be used for standard proctor testing?

Method B for standard proctor testing is specifically applied when the material being tested has 25% or less retained on a 3/8" sieve. This method is utilized for finer materials that are expected to exhibit better compaction characteristics and more consistent moisture-density relationships. The use of Method B is important because it provides a more accurate representation of the compaction characteristics for these specific soil types, helping engineers and technicians achieve reliable results for construction and earthwork projects.

The focus on 25% or less material retained on the 3/8" sieve ensures that the soil sample is sufficiently fine-grained, allowing for effective compaction testing. This threshold is critical because it differentiates between different testing methods based on the grain size distribution of the soil, which can influence the compaction behavior significantly. Thus, using Method B under these specific conditions helps ensure that the results will accurately reflect the materials' compaction properties.