Per AASHTO R 90, what minimum mass and maximum nominal size should be sampled?

• A. At least 10 kg with nominal max size 4.75 mm
• B. At least 25 kg with nominal maximum size 19 mm
• C. At least 50 kg with nominal max size 37.5 mm
• D. At least 5 kg with nominal max size 19 mm

Answer: (B)

AASHTO R 90 bases the amount you sample on how large the aggregate particles are. The bigger the largest particle, the more material you need to grab a representative chunk for all the lab tests that follow (like gradation and asphalt content). For a mixture with a maximum nominal size of 19 mm, the standard calls for at least 25 kg of material to be sampled. That ensures the sample is large enough to be representative when splitting and testing in the lab.

The other options don’t fit that guideline: a larger maximum size would require more mass (for example, 37.5 mm calls for about 50 kg), while a smaller maximum size would require less mass (4.75 mm would be around 10 kg). A too-small sample mass for the given maximum size wouldn’t provide a representative portion for testing.