Which statement is true about sieve sizes used when washing?

Which statement is true about sieve sizes used when washing?

• A. Upper sieve openings 2.36 mm ( #8 ) and 1.18 mm ( #16 ), and a 75-μm ( #200 ) lower sieve.
• B. Upper sieve openings 4.75 mm and 2.36 mm, and a 600-μm lower sieve.
• C. Three sieves with equal openings.
• D. Lower sieve is 2.36 mm.

Answer: (A)

When washing aggregates, the goal is to separate the material by size while removing clay and fines with the wash water, so you end up with the right distribution after washing. Using two small upper screens and a very fine lower screen is a common setup because it provides staged classification and effective fines control. Having upper openings of 2.36 mm and 1.18 mm lets you separate the mid-sized and finer fractions before the finest material is collected, while the bottom sieve of 75 μm captures the finest material. This ensures the coarser fractions stay in their proper size ranges and the fines are isolated for proper washing and disposal, which helps the final aggregate meet performance specs for asphalt. Options with a coarser lower sieve (like 600 μm) would let too many fines pass through, making the classification ineffective; three sieves with equal openings wouldn't properly separate the size ranges; and a lower sieve of 2.36 mm wouldn’t capture the fines needed for accurate washing and disposal.

When washing aggregates, the goal is to separate the material by size while removing clay and fines with the wash water, so you end up with the right distribution after washing. Using two small upper screens and a very fine lower screen is a common setup because it provides staged classification and effective fines control.

Having upper openings of 2.36 mm and 1.18 mm lets you separate the mid-sized and finer fractions before the finest material is collected, while the bottom sieve of 75 μm captures the finest material. This ensures the coarser fractions stay in their proper size ranges and the fines are isolated for proper washing and disposal, which helps the final aggregate meet performance specs for asphalt.

Options with a coarser lower sieve (like 600 μm) would let too many fines pass through, making the classification ineffective; three sieves with equal openings wouldn't properly separate the size ranges; and a lower sieve of 2.36 mm wouldn’t capture the fines needed for accurate washing and disposal.