Density and Specific Gravity:

Bulk Density

The density of aggregate-material and the density of aggregate-sample are different in the sense that latter is defined as the weight of the sample of aggregates that would fill a unit volume in a standard manner. The sample of aggregates always has the volume occupied by voids and the solid aggregate. That is why the density of aggregate sample is designated as bulk density of aggregate. It depends on how densely an aggregate are packed which further depend on the shape, size, grading and moisture content of the aggregates. Then, higher bulk density indicates lesser voids.