Sand and gravel are aggregates don't call them inert because:

Sand and gravel are technically called aggregates and not as they are erroneously inert because they can intervene in chemical reactions that lead to the solidification of mortars and concretes.

The grain size

The sands are divided according to the granulometry (the size of the grains that compose them) into fine, medium and coarse sand.

The greater the fineness of the sands and the greater their workability. The greater the size and quality of the aggregates, the greater their mechanical characteristics.

The granulometric division is obtained simply by passing the sands through special sieves.