Evaluation of The Effect of Gradation on Mechanical properties of Stone Mastic Asphalt Mixtures

Abstract

For stone mastic asphalt (SMA) mixtures, the aggregate gradation is the significant requirement to achieve the best structural design. In this research, an attempt to evaluate the effect of nominal maximum aggregate size (NMAS) and gradation on SMA volumetric and mechanical properties. Samples for each mixture were designed and fabricated according to NAPA specifications. A total of 9 SMA mixtures with three NMASs, each with three different aggregate gradations, one asphalt binder (styrene butadiene styrene SBS) modified binder were studied. Volumetric analysis of specimens revealed that the voids in the mineral aggregate (VMA), and voids filled with asphalt (VFA) rise with a reduction in NMAS. SMA samples with higher NMAS have lower optimum asphalt than those of lower NMAS. From the laboratory study, SMA mixes fabricated utilizing the upper limit of gradation showed the highest mechanical properties in terms of Marshall Stability and indirect tensile strength. It was recorded also that the SMA mixtures with larger NMAS had higher ITS and Marshall stability contrasted to the others. This improvement could be because of the larger portion of coarse aggregate in the SMA mixture.