What is the purpose of grouping dry and wet subsets by similar air voids?

• A. To minimize aggregate cost
• B. To ensure comparability of results between subsets
• C. To increase air voids difference
• D. To simplify testing

Answer: (B)

Grouping dry and wet subsets by similar air void content targets a major source of variation in asphalt mixtures. The amount of void space inside a compacted sample directly affects properties like stiffness, strength, permeability, and moisture susceptibility. If two subsets have different air voids, you can’t tell whether a difference in test results comes from the factor you’re studying or simply from density differences. By matching subsets to have comparable air voids, you ensure that observed differences are due to the variable under investigation, making comparisons between subsets meaningful and reliable. In practice, you adjust compaction or specimen preparation to hit a similar air void percentage and verify it before testing. This leads to more consistent, interpretable results.