The growing demand for sustainable and high-performance asphalt binders has prompted the exploration of waste-derived modifiers. This study investigates the performance enhancement of Natural Asphalt (NA) using Sugarcane Molasses (SM) and Waste Engine Oil (WEO). The modified blends were prepared by partially replacing 50 % NA with varying proportions of SM and WEO ranging from 10 % to 40 % of the total weight of NA. Comprehensive testing was conducted, including penetration, softening point, ductility, viscosity, Bending Beam Rheometer (BBR), Multiple Stress Creep Recovery (MSCR), Energy Dispersive X-ray Spectroscopy (EDX), Fourier Transform Infrared (FTIR) spectroscopy, and Scanning Electron Microscopy (SEM). The results demonstrated that modified blends with a high WEO content significantly increased fluidity, reducing rotational viscosity by up to 91 % for the blend with 40 % WEO and 10 % SM at 135 ◦C. Conversely, higher SM content increased stiffness, as seen in the blend with 40 % SM and 10 % WEO, with penetration values rising by 305 % compared to unmodified NA. Rheological testing showed that the 40 % SM and 10 % WEO blend achieved the highest rutting resistance with a Performance Grade (PG) of 88 ◦C, while the 40 % WEO and 10 % SM blend exhibited the best fatigue resistance with a 55 % reduction in G* .sinδ. Low-temperature performance was significantly improved across all blends, with the 40 % WEO and 10 % SM blend achieving the lowest creep stiffness and highest m-value, ensuring superior thermal cracking resistance. Chemical analysis revealed increased oxygen content (18.6 %) and reduced sulfur content (60 %) in the 40 % SM and 10 % WEO blend, indicating enhanced oxidation resistance. SEM analysis confirmed the development of dense morphology in the 40 % SM and 10 % WEO blend, correlating with superior structural integrity. Grey decision analysis identified the 40 % SM and 10 % WEO blend as the optimal blend with the lowest bull’s-eye distance, reflecting balanced performance across all parameters. These findings highlight the complementary effects of SM and WEO in enhancing the performance of NA, with the 40 % SM and 10 % WEO blend emerging as the most promising blend for bio-asphalt applications.
