Development, characterization, and multi-response optimization of waste cooking oil and rice husk ash modified bio-bitumen under unaged and short-term aged conditions

Abstract

The increasing demand for sustainable pavement materials has promoted the use of waste-derived modifiers as partial alternatives to conventional petroleum bitumen. This study investigates the effects of waste cooking oil (WCO) and rice husk ash (RHA) on the physical, rheological, temperature-susceptibility, temperature-sensitivity, chemical, and workability characteristics of VG-30 bitumen. Waste cooking oil-modified bio-bitumen (WCOMBB) was prepared using 5–15% WCO, while rice husk ash-modified bio-bitumen (RHAMBB) was prepared using 3–9% RHA by weight of base binder. Conventional binder tests, viscosity analysis, mixing and compaction temperature evaluation, activation energy analysis, Dynamic Shear Rheometer (DSR)-based frequency sweep, master curve analysis, Fourier transform infrared spectroscopy (FTIR), and Grey Relational Analysis (GRA) were conducted under unaged and short-term-aged conditions. The results showed that WCO significantly softened the binder by increasing penetration up to 307.9% and reducing absolute viscosity up to 83.1%, thereby improving workability and reducing processing temperatures. In contrast, RHA improved binder stiffness by reducing penetration up to 57.1% and increasing viscosity up to 19.8%, indicating better thermal stability and high-temperature consistency. Rheological results showed that WCOMBB-10% exhibited improved flexibility, whereas RHAMBB-9% showed enhanced stiffness and rutting-related response. FTIR indices indicated physical blending for WCOMBBs and filler reinforcement for RHAMBBs without major new chemical bond formation. GRA identified 15% WCO and 9% RHA as the best-ranked dosages within the selected binder-level criteria. Overall, WCO is promising for warm-mix applications, while RHA is suitable for high-temperature binder improvement.