Microscopic Analysis of Activated Crumb Rubber and Its Effect on Mechanical Performance of Asphalt Mixtures Using Dry Process

Abstract

Crumb rubber (CR) from grinding waste tires has served as an asphalt modifier in asphalt pavement construction for decades. Incorporating CR in asphalt mixtures by the dry method is becoming popular with the emphasis on low carbon emissions, greenness, and sustainability. However, the poor compatibility and mechanical performance of dry-mixed asphalt rubber limit its application. This work presents the effect of practical activation treatments on the microstructure of CR and mechanical properties of the resulting asphalt binder and mixtures, aiming to modify CR surface features and improve the performance of asphalt mixtures. According to previous work, the activation treatment methods of high-temperature, preswelling, the two combinations, and microwave irradiation for CR were compared. Meanwhile, the surface morphology, chemical features, and dispersion degree of various activated CR as well as rutting resistance, low-temperature performance, and moisture stability of the resulting asphalt and asphalt mixtures were evaluated. The results indicated that selected activation methods significantly change the surface morphology and chemical features of CR, and the activated CR shows a flocculent structure with porous surface and reactivity. Preswelling with high-temperature and microwave activation for CR endows the modified asphalt with significantly improved viscoelastic properties. Preswelling with high-temperature activated CR asphalt shows better low-temperature cracking resistance. Asphalt modified with activated CR presents homogeneous and compatible states in microscopy compared with ordinary asphalt rubber. Incorporating activated CR in asphalt mixtures by the dry method is a promising technique in view of improved low-temperature cracking resistance and moisture stability.