The maximum size of aggregate is defined as the aperture of the sieve retaining 15 percent or more of the particles present in the aggregate sample. The aggregate's maximum size impacts the concrete's water requirement, workability, and strength. Larger aggregates reduce the surface area needing cement paste coverage, which can lower water needs, thereby allowing a decrease in the water-to-cement ratio when the desired workability and richness of the mix are to be maintained, which can result in enhanced concrete strength. However, too-large aggregates may weaken concrete by reducing the aggregate-cement bond area and introducing discontinuities, leading to a heterogeneous mix. The optimal maximum size of aggregate depends on the specific application, but for most structural concrete, it is typically limited to either 25 mm or 40 mm. The size is constrained by the dimension of the concrete member, the space between reinforcing bars in the member, and a balance between the cost of managing various aggregate sizes and the risk of segregation during placement.
