Which sieves cannot be changed for gradation targets?

The correct choice is based on the critical role that specific sieves play in determining the proper gradation of aggregate used in asphalt and concrete mixtures.

The top sieve refers to the largest mesh size in the grading system, which effectively controls the upper limits of aggregate size. Altering the top sieve would significantly affect the overall proportion of coarse aggregates in the mix, altering performance characteristics such as workability and load-bearing capacity.

The bottom sieve, on the other hand, dictates the smallest particle size that can be used, which directly impacts the filler and fine aggregate content. If the bottom sieve is adjusted, it can affect the void space and packing of the aggregates, which is vital for ensuring a solid bond in the final mix.

The #200 sieve specifically evaluates particles that are finer than 0.074 mm, which contributes to the cohesiveness and workability of the mix. This size plays a crucial role in preventing segregation and ensuring that the smaller particles fill the voids between larger aggregates.

Together, these sieves (the top, bottom, and #200) must remain unchanged to maintain the integrity of the aggregate gradation, as they are fundamental to achieving the desired performance characteristics of the material. Adjusting other sieves may influence gradation