Influence of crumb rubber particle content and size on stone mastic asphalt: a sustainable approach to asphalt pavement

Despite having certain limitations, stone mastic asphalt (SMA) is now widely adopted for the pavement to solve the problems of HMA pavement distress because of its strong stone-to-stone bonding and higher asphalt content. To increase this bonding among the aggregates and asphalts, crumb rubber, cheaply available in the environment, can be utilized to produce sustainable pavement. However, the volumetric and mechanical qualities may be adversely affected by an overabundance of rubber and its size. Therefore, this study focused on the identification of the optimum crumb rubber content and size and its effect on the volumetric properties, and Marshall Stability, flow, and moisture susceptibility of SMA. Nine variations, with 10, 15, and 20% rubber of 4.00–2.36, 2.36–1.18, and 1.18–0.075 mm, were employed using the dry process to modify the control SMA designed by the Marshall Method. The volumetric properties of SMA were better affected by 10–15% finest (1.18–0.075 mm) rubber. The inclusion of the finest crumb rubber (10–15%) improved SMA’s Marshall Stability and moisture damage resistance, while the mixture became more flexible, as indicated by the flow value, as rubber amount and size increased. Without compromising the volumetric requirements for an SMA mixture, this rubber strengthened the control SMA’s stability and moisture damage resistance from 1500.7 lb to 1707.4 lb and 85% to 86%, respectively. Based on a thorough evaluation of findings and ANOVA, up to 15% finest crumb rubber was found to be optimal for SMA, providing superior unit weight, stability, and durability against moisture exposure.