From Waste to Pavement: Used Motor Oil Rejuvenation of Guayule Resin–Crumb Rubber Sustainable Asphalt Binders

This study evaluated waste-derived used motor oil (UMO) as a rejuvenator in sustainable asphalt binders incorporating guayule resin and crumb rubber modifier (CRM). Guayule resin is a bio-based by-product of natural rubber extraction exhibiting asphalt-like characteristics. While it offers environmental benefits and resists oxidative aging due to natural antioxidants, its intrinsic stiffness limits performance at intermediate and low temperatures. CRM enhances elasticity and rutting resistance but further amplifies stiffness when combined with guayule. A hybrid binder system, designated ARG75(20):25, was formulated with 75% asphalt rubber and 25% guayule resin (12.5% CRM by total binder weight), with a continuous performance grade (PG) 73-16. To restore viscoelastic balance across service temperatures, UMO was incorporated at 1%, 3%, and 5%, targeting base asphalt grade PG 64-22. Rheological properties were assessed under original, RTFO-, and PAV-aged conditions using dynamic shear rheometer (DSR), bending beam rheometer (BBR), and black phase analysis. PG and viscoelastic metrics were used to evaluate aging response, rutting and fatigue potential, as well as low-temperature stiffness and relaxation. Results showed that UMO reduced binder stiffness and improved relaxation behavior, significantly enhanced fatigue and thermal cracking resistance without compromising rutting tolerance. The 3% UMO dosage yielded the most balanced formulation, restoring the PG grade to 66-22 and meeting Superpave criteria. Black phase analysis confirmed enhanced compliance, and BBR at -12  validated low-temperature cracking resistance. Compared to the PG 64-22 benchmark, UMO-ARG binders delivered comparable or superior performance while displacing ~40% of petroleum asphalt with recycled and bio-based materials, supporting circular economy goals.