Quality control for natural sand content of asphalt concrete

Excessive natural sand contents can increase the susceptibility of asphalt concrete to permanent deformation-type distresses. For this reason, pavemen t construction specifications usually include a limit for the proportion of natural sand that can be included in an aggregate blend. Although proporti ons of natural sand are controlled during the development of asphalt mixtur e designs, direct methods for monitoring natural sand contents are typicall y not included as part of construction quality control plans. The packing d ensity of free-fallen aggregates, which can provide an indirect measure of particle angularity and surface texture, shows promise as a tool for monito ring natural sand content in aggregate blends. In the laboratory study pres ented in this paper, the free-fallen packing densities of aggregates extrac ted from;asphalt concrete permitted predictions of natural sand contents to within approximately 5%. When used as a quality control tool in this study , these packing density measurements effectively identified changes in the natural sand content of asphalt concrete.