Rutting and fatigue performance of high-dosage crumb rubber modified bitumen

Abstract

This study investigates the effects of crumb rubber (CR) modification on the rheological and performance characteristics of asphalt binders, with a focus on rutting and fatigue resistance. Modified binders were prepared with CR contents 10%, 15%, 20% and 24% by weight of viscosity grade-30 (VG-30) binder. These binders were evaluated using Dynamic Shear Rheometer (DSR), Multiple Stress Creep Recovery (MSCR), Zero Shear Viscosity (ZSV), Shenoy parameter, and the Linear Amplitude Sweep (LAS) test. The addition of CR significantly increased the complex shear modulus (G*) and storage modulus (G′) by up to 3.1 and 30.3 times respectively, while reducing the phase angle (δ) by up to 34.6°, indicating improved stiffness and elasticity. Enhanced values of G*/sin δ and Shenoy parameter increased by 5.34 and 10.4 times respectively for CR24 binder demonstrating improved rutting resistance. MSCR results showed percent recovery increased from -0.2% to 75.1%, and non-recoverable creep compliance (J_nr) decreased from 2.81 to 0.07 kPa⁻¹. The Rutting Resistance Index Ratio (RRIR) was effective in evaluating crumb rubber modified bitumen (CRMB) performance with J_nr showing the highest sensitivity to CR content, establishing it as robust indicator of rutting resistance. Fatigue analysis revealed that the binder with 20% CR offered the best balance between fatigue resistance and strain tolerance, identifying it as the optimal dosage. A strong inverse correlation with r-square value 0.91 was found between elastic recovery (ER-DSR) and Jnr, and a moderate positive correlation with r-square value 0.68 between ER-DSR and fatigue life (N_f), highlighting the interconnected nature of elasticity, rutting resistance, and fatigue performance.