The effects of coarse aggregate cleanliness on asphalt concrete compactability and moisture susceptibility

Twelve field projects were studied where forty-four locations were evaluated to assess the cause or causes of asphalt concrete that exhibits 'tender zone' characteristics and to investigate the tendency of these mixes to be susceptible to moisture damage. Data was collected during construction and samples were obtained to conduct laboratory tests. Field and laboratory data was used to develop multiple regression equations to predict final in place air voids and moisture susceptibility. The overall conclusion was that compactability appeared to be predicted in a reasonable manner while moisture susceptibility did not. The Methylene Blue test appears promising when used in conjunction with cold feed and/or mix moisture as a means of providing guidance for achieving higher in place density. The tensile strength ratio (TSR) test as performed in this research on laboratory compacted specimens was found to be questionable in terms of its ability to predict field moisture susceptibility.