The percentage of fines passing the No. 200 US Standard sieve in the A-2-4 material should not exceed?

• A. 10%
• B. 12%
• C. 15%
• D. 20%

Answer: (C)

The key idea is controlling how many fines the material contains, as measured by the percentage passing the No. 200 sieve. For A-2-4 material, keeping fines at or below 15% preserves the mostly coarse-grained nature of the mix, which is important for interlock between larger pieces, strength, and, importantly, drainage. If too many fines pass the No. 200 sieve, the material becomes too plastic and weather-sensitive, reducing permeability and making compaction and bearing capacity less reliable. That’s why 15% is the maximum—low enough to maintain good drainage and structure, but not so low as to overly restrict workable material. The other values would either be too strict or too permissive for this type of material, risking either poor compaction or excessive fines that degrade performance.