What are considered critical sieves in aggregate gradation?

In the context of aggregate gradation, critical sieves are those that significantly impact the performance of the mix design, especially in terms of strength, workability, and durability of the final product. The top sieve is crucial as it indicates the largest particle size and influences the void structure of the aggregate. The bottom sieve (also known as the smallest sieve) is critical as it helps determine the amount of fine materials in the sample, which can affect the wetness and workability of the concrete or asphalt mixture. The #200 sieve is significant because it captures the fine particles and dust that can greatly influence water demand and cohesiveness in the mix.

By focusing on these three specific sieves—the top sieve, the bottom sieve, and the #200 sieve—technicians can effectively assess and manage the gradation of aggregates to ensure optimal performance in construction applications. This combination provides essential information for evaluating how the aggregate blends together and interacts with binder materials, which is central to achieving desired properties in asphalt or concrete mixes.