The porosity of aggregate refers to the volume of pores in the aggregate.

These pores vary in size and are either enclosed within the aggregate or interconnected and open to its surface, through which the water or other fluids can enter the aggregates.

A saturated surface-dry state implies that all aggregate pores are filled with moisture, yet the surface is dry.

Meanwhile, a moist state indicates the presence of excess moisture on the surface of the saturated aggregate.

When aggregate in a saturated surface-dry state is exposed to air, some moisture evaporates from the pores, resulting in an air-dry state.

When oven-dried, complete moisture evaporates from the aggregate pores, signifying a bone-dry state.

Water absorption is calculated as the difference in the mass of the aggregate between the saturated surface-dry state and the bone-dry state, expressed as a percentage of the sample's dry mass.

Lastly, water absorbed in the pores of aggregates in concrete will not be available to hydrate cement or improve concrete workability.

Moreover, when subjected to freeze-thaw cycles, this absorbed water may cause the aggregate to disintegrate.