Design and performance of stone mastic asphalt

Accurate quantification of aggregate gradation is essential for a better understanding of its effect on the load-carrying capacity of an asphalt mixture. This is even more applicable for stone mastic asphalt (SMA), where stone-to-stone contact forms the cornerstone of its load-carrying capacity, especially against rutting. This paper presents a mix design procedure, which is based on and adapted from the Bailey method, to objectively quantify stone-to-stone contact for SMA mixtures. A total of 16 asphalt mixtures with six different aggregate gradations and three different asphalt binder contents were studied. Volumetric analysis of specimens showed that the volume of coarse aggregate in the mixtures had a significant effect on the voids in the coarse aggregate and the voids in the mineral aggregate (VMA). The coarse aggregate stone-to-stone contact was developed when the volume of coarse aggregate was in the range of 95–105% of the rodded unit weight. Asphalt binder content at 5.5% was optimal for the des...