Aggregate specific gravity and bulk density: what is the difference?

Particle properties and a pile of aggregate are different measurements

Relative density, often called specific gravity, is dimensionless. Particle density relates particle mass to a defined particle volume. Bulk density of an aggregate pile or test container also includes interparticle voids. These distinctions matter whenever mass is converted to volume: using particle density for stockpile capacity omits the spaces between stones. Dry, saturated-surface-dry and apparent results must not be interchanged without understanding the method. Loose and compacted bulk densities also describe different packing conditions. ASTM C127 and C128 address coarse and fine particle properties respectively, while C29/C29M addresses aggregate bulk density and voids. A useful report identifies the sample, method, units, moisture state and filling condition. The Persian article develops original hypothetical examples, explains unit conversion and discusses why a larger reported density is not automatically evidence of better railway ballast.