Editing Aggregate (composite) (section)

===Aggregate size===
Experiments and mathematical models show that more of a given volume can be filled with hard spheres if it is first filled with large spheres, then the spaces between ([[Wiktionary:interstice|interstices]]) are filled with smaller spheres, and the new interstices filled with still smaller spheres as many times as possible. For this reason, control of ''particle size distribution'' can be quite important in the choice of aggregate; appropriate simulations or experiments are necessary to determine the optimal proportions of different-sized particles.

The upper limit to particle size depends on the amount of flow required before the composite sets (the gravel in paving concrete can be fairly coarse, but fine sand must be used for [[tile]] [[mortar (masonry)|mortar]]), whereas the lower limit is due to the thickness of matrix material at which its properties change (clay is not included in concrete because it would "absorb" the matrix, preventing a strong bond to other aggregate particles). Particle size distribution is also the subject of much study in the fields of [[ceramic]]s and [[powder metallurgy]].