Strength and durability of dry-processed stone matrix asphalt containing cement pre-coated scrap tire rubber particles

Application of rubber particle from the scrap tire through dry-process is a practical and economical efficient way to resolve the recycling problem and environmental concern of the disposed tires. However, the added rubber aggregate reduces both the strength and durability of the rubberized asphalt mixture. This study aims to improve the strength and durability of dry-processed asphalt mixture by using the cement (Portland Type Ⅰ) coating methods and gap-gradation system (Stone Matrix Asphalt (SMA)). The cement coating was applied to enhance the bonding performance between rubber aggregate and asphalt binder, and limits its expansion due to swelling in hot asphalt binder. The SMA mixtures were prepared with different sizes and proportions of mineral aggregates. The samples with conventional aggregate and untreated rubber aggregate both serve as control samples for the sample evaluation. Finally, tests on tensile strength, moisture susceptibility, rutting resistance, anti-stripping resistance, fatigue cracking resistance, and bonding between rubber particles and asphalt binder of SMA mixtures were conducted. The results showed that SMA mixture with pre-coated rubber aggregate owns similar performance comparing to the samples prepared with conventional aggregate and also has higher strength and better performance than that of the mixture with untreated rubber aggregate. Results also clearly indicated that the asphalt mixtures with 50% of No.16 mineral aggregates replaced by pre-coated rubber aggregates performed the best-satisfied performances; while, with a further increase in replaced size or proportion, the satisfied performances of SMA mixtures would be degenerated