Integrated Application of Waste Cooking Oil, Reclaimed Asphalt Pavement, and Fly Ash in Sustainable Flexible Pavement Systems

The increasing scarcity of natural aggregates and petroleum-based binders has intensified the need for sustainable alternatives in flexible pavement construction. Simultaneously, the disposal of industrial by-products and roadway wastes presents serious environmental challenges. This study investigates the integrated use of waste cooking oil (WCO), reclaimed asphalt pavement (RAP), fly ash (FA), and bottom ash (BA) to enhance the performance of flexible pavements. Short-term aging of bitumen was simulated using the Rolling Thin Film Oven Test (RTFOT), followed by rejuvenation with varying dosages of WCO. Binder performance was evaluated through penetration, softening point, ductility, viscosity, flash point, and fire point tests. RAP mixtures incorporating rejuvenated binders were designed using Marshall methodology. FA and BA stabilized subgrades reinforced with polypropylene fibers (PPF) were assessed through CBR and triaxial testing. Finite Element Analysis (FEA) was conducted to evaluate pavement response under axle loading and validated using laboratory plate load tests. Results demonstrate that an optimum WCO dosage effectively restores aged bitumen properties, while stabilized subgrades significantly reduce pavement thickness and construction cost. The combined use of WCO, RAP, and fly ash offers a technically viable and environmentally sustainable solution for flexible pavement construction.