Experimental Investigation of Stone Matrix Asphalt Mixtures

Abstract

Stone Matrix Asphalt (SMA) is gap graded bituminous mixture, having higher proportions of coarse aggregates and bituminous binder, yielding better rut resistance and durability than conventional dense graded mixes. The skeleton of coarse aggregates has stone on stone contact between them, which is a major requirement for this mixture. The gap graded aggregate structure and higher binder and filler content may lead to drain down in loose SMA at elevated temperatures, and it is controlled generally by using a suitable stabilizing additive in the mixture. In the current study, SMA mixtures were prepared with two aggregate gradations having two nominal maximum aggregate sizes, 16mm and 13.2mm, and are named as SMA 1 and SMA 2. Viscosity Graded (VG) 30 bitumen, Crumb Rubber Modified Bitumen (CRMB) and Polymer Modified Bitumen (PMB) of two grades, 40 and 70, were used as binders, and three types of fibers, pelletized Cellulose Fiber (CF), Coconut Coir (CC) and Sisal Fiber (SF), and Shredded Waste Plastics (SWP) were used in mixtures with VG 30 bitumen to control drain down. Fiber content was limited as 0.3% by weight of mixture, based on drain down test results, whereas SWP content was selected 4, 8, 12 and 16 % by weight of bitumen. Drain down was within specified limits for all mixtures and decreased with increase in fiber and SWP content. The specimens were prepared as per Marshall mix design and were compacted in Superpave Gyratory Compactor (SGC). The performance of these mixtures were assessed in laboratory through Volumetric and Marshall properties, Indirect Tensile (IDT) strength, rutting and fatigue behaviour and moisture susceptibly characteristics. In general, mixes with PMB 40 and CF, showed better properties among mixes with modified binder and fiber additives respectively. In case SWP mixtures, 8 and 12% plastic content produced better mixtures. For all mixture types, SMA 1 gradation showed better results than SMA 2, except for moisture susceptibility, where both gradations performed almost same. Cost analysis of all prepared mixtures was carried out based on the standard rates, and cost for one cubic meter mixture was determined.