EVALUATION OF STONE-ON-STONE CONTACT IN STONE-MATRIX ASPHALT

Abstract

The presence of stone-on-stone contact and a relatively low percentage of fine aggregate are two characteristics of stone-matrix asphalt (SMA). Although it is known that the stone skeleton in SMA is primarily responsible for its high rutting resistance, a method to quantitatively determine stone-on-stone contact has not been used in the United States. A simple laboratory method was developed to determine stone-on-stone contact in SMA with conventional hot-mix asphalt parameters such as voids in mineral aggregate, voids in coarse aggregate, and dry-rodded weight of coarse aggregate. Tests were conducted to evaluate the effect of percent passing the 4.75-mm sieve on the susceptibility of mix stability to change in void content. It was observed that mixes with a low percent passing the 4.75-mm sieve were less sensitive to low air void contents. Mixtures with a low percent passing the 4.75-mm (No. 4) sieve (30 percent or less) tended to have stone-on-stone contact.