The moisture content of the aggregate is the excess water present on the surface of the aggregate that exists in a saturated and surface-dry state.

It is measured using a buoyancy meter test.

For a moist aggregate, the sum of its water absorption and moisture content gives its total water content.

It is determined using an oven in the laboratory or electric devices fixed in aggregate storage bins.

When a stockpile of sand is exposed to rain and sun, it may retain free moisture on the surface of sand grains in the pile's interior.

This free moisture pushes apart the adjacent sand grains, increasing the volume of a given sand mass, referred to as the bulking of sand. 

Bulking of sand contributes to a lesser mass of sand occupying a definite volume.

During weigh batching for concrete, additional sand is added to compensate for the volume increase caused by moisture, and the corresponding amount of water is subtracted from the mix to account for the moisture already present in the sand.