Method To Ensure Stone-on-Stone Contact in Stone Matrix Asphalt Paving Mixtures

Abstract

The use of stone matrix asphalt (SMA) has continued to rise in the United States because of its ability to withstand heavy traffic without rutting. This ability is derived from a stone-on-stone coarse aggregate skeleton. While this coarse aggregate skeleton is imperative for SMA to perform, no quantitative method exists to measure it. A method for determining when stone-on-stone contact exists is presented. The proposed method first determines the voids in the coarse aggregate (VCA) for the coarse aggregate–only fraction of the SMA mixture. Second, the VCA is determined for the entire SMA mixture. When the two VCA values are compared, the VCA of the SMA mixture should be less than or equal to the VCA of the coarse aggregate–only fraction to ensure that stone-on-stone contact exists in the mixture. Five different methods for determining the VCA of the coarse aggregate–only fraction were used to see which performed best and was the most practical. The aggregate degradation produced by each of the five methods was also determined and compared with the coarse aggregate breakdown produced in an SMA mixture compacted with 50 blows of a Marshall hammer. The results indicate that the Superpave gyratory compactor and dry-rodded methods produced the best results. Both methods are recommended for further testing.