Effect of re-refined engine oil bottoms on rutting and fatigue performance of EVA-modified bitumen

This study investigated the effect of re-refined engine oil bottoms (REOB) on the morphological, chemical, physical and rheological performance of 50/70 penetration-grade bitumen modified with 5% ethylene–vinyl acetate (EVA). REOB was utilized specifically as a balancing agent to mitigate the excessive stiffness and workability issues typically induced by plastomeric polymers like EVA. REOB was incorporated into EVA-modified bitumen at 2%, 4%, 6%, 8%, and 10% by weight of the base bitumen. The binders were evaluated using conventional tests, temperature sweep, multiple stress creep and recovery (MSCR), linear amplitude sweep (LAS), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) analysis under unaged, rolling thin-film oven (RTFO)-aged, and pressure aging vessel (PAV)-aged conditions where applicable. REOB increased penetration by up to 50.0% and reduced softening point and viscosity (by up to 5.0% and 26.5%, respectively), indicating improved workability of EVA-modified bitumen. Rheological results showed that REOB partly reduced the high-temperature rutting resistance provided by EVA (decreasing the |G*|/sinδ parameter by up to 30% in the unaged state), but improved intermediate-temperature fatigue-related response and preserved a more ductile damage behaviour in the LAS test. The results indicate that EVA + REOB composite modification provides a performance balance between rutting resistance, workability, and fatigue response, with the suitable REOB dosage depending on the intended service conditions.