Experimental investigation of the effect of polyphosphoric acid on bitumen containing crumb rubber and waste engine oil

The depletion of petroleum-based bitumen resources and growing environmental concerns from waste disposal have prompted the search for sustainable additives in pavement engineering. This study addresses the gap in understanding the combined effects of Waste Engine Oil (WEO), Crumb Rubber (CR), and Polyphosphoric Acid (PPA) on the properties of 60/70 penetration grade bitumen. The research focuses on producing partially synthetic bitumen by blending various combinations of WEO (5–15%) and CR (20–30%) with PPA (0.6–1.8%). The methodology involved testing the modified binders’ penetration, viscosity, softening point, rheological properties, and bitumen bond strength. Results showed that including WEO and CR reduced penetration by up to 20%, decreased the softening point by 15%, and lowered viscosity by 10%. However, adding PPA significantly improved rheological behavior by 20%, increased viscosity by 15%, and enhanced bonding strength by 25%. The optimal combination—30% CR, 5% WEO, and 1.8% PPA—demonstrated a notable 15% increase in viscosity at high temperatures and a 20% improvement in rheological properties compared to base bitumen. These findings support using this formulation as a cost-effective and environmentally friendly alternative for road paving applications. Further extensive testing, including asphalt field trials, is recommended to validate the laboratory results, with the potential to replace up to 35% of virgin binder with industrial waste.