Thermal effects on rheological characteristics and its evolution mechanism of bio-modified rubberized asphalt for sustainable road system: a focus on rubber particle size

Bio-modified rubberized asphalt (BMR) has been acclaimed for its superior pavement performance and eco-friendliness, which can promote the sustainability of road systems. However, its rheological properties, intimately tied to crumb rubber (CR) particle size, display variability during thermal storage. This study probed the effect of CR particle size on BMR's rheological attributes under thermal conditions. BMRs were prepared using varied CR particle sizes, thermally conditioned over a span of up to 10 hours, and then tested for rheological properties. Our findings illustrate particle size's pivotal role in CR swelling, degradation, and asphalt aging mechanisms during thermal conditioning, consequently affecting various BMR characteristics. Large CR particles displayed slower swelling rates, with secondary swelling observed. The CR's micro-skeleton within asphalt phase amplified asphalt's elasticity recovery, causing an increased rutting factor and complex viscosity. In contrast, stress concentration due to CR particles curtailed the fatigue life of BMR. With smaller CR particles, both elastic response and viscosity of BMR diminished due to CR's devulcanization and depolymerization during thermal conditioning. However, substances released during CR degradation altered the asphalt composition, bolstering BMR's fatigue resistance. During thermal process, asphalt oxidation resulted in increased stiffness, thereby degrading BMR's rheological properties. It is beneficial for CR of 40 mesh or coarser to extend the breeding time to stabilize its performance, whereas for asphalt prepared with 60 mesh or finer CR, it should be used as soon as possible after preparation to prevent a significant performance degradation. In summary, managing particle size and thermal conditioning time is crucial in preserving BMR's optimal rheological properties.