In concrete, coarse aggregate is the material retained on which sieve number?

• A. 2
• B. 3
• C. 4
• D. 5

Answer: (C)

Coarse aggregate is defined by particles that are large enough not to pass through a 4.75 mm sieve. In a sieve analysis, you separate the sample by passing it through progressively finer sieves; the portion that remains on the sieve with 4.75 mm openings is the coarse aggregate. The material that passes through that sieve is the fine aggregate. So the correct boundary is the 4.75 mm sieve, which is why the coarse portion is retained there.