Dry subset samples and wet subset samples should be grouped so that the average air voids for each subset is about the same.

• A. Not specified
• B. False
• C. True
• D. Only if recommended

Answer: (C)

The idea being tested is balancing the samples to reduce bias when comparing different moisture conditions. Air voids are a fundamental property that reflects how densely the asphalt mix has been compacted; they can vary from sample to sample. By grouping the dry subset and the wet subset so that each group has about the same average air void content, you ensure that any differences you observe between the dry and wet conditions come from the moisture effect (or the testing setup) rather than from one group starting with more or fewer air voids. This makes comparisons fair and the results more reliable.

In practice, you’d measure the air voids across the candidate samples and assign them to the two subsets so their mean air void values are very close. If needed, you’d swap samples to keep the averages aligned. This balancing act is standard practice because it controls for natural variation in air voids and isolates the variable you’re studying.

So, it’s true because balancing the averages improves the validity of comparing dry versus wet samples, not because it’s optional or undefined.