Sustainable Cutback Bitumen from Transesterified Waste Cooking Oil: Development, Characterization, and Performance

Sustainable and environmentally responsible alternatives to conventional diesel-based cutback bitumen are increasingly needed in pavement construction due to the environmental impacts of diesel, dependence on nonrenewable resources, and safety concerns linked to low flash and fire points of the cutback bitumen. This study investigates the development of a diesel-reduced cutback system using fatty acid methyl esters (FAME) derived from waste cooking oil (WCO), with emphasis on reducing volatility, improving mechanical performance, and lowering environmental burdens. FAME was synthesized through the transesterification of WCO using an optimized methanol-to-oil ratio of 12:1 and blended with diesel at various proportions. Volatility, viscosity, Fourier transform infrared characterization, and shear strength tests were performed to assess the physical, chemical, and mechanical behavior of the blends. The results showed that FAME-modified cutbacks exhibited lower volatility and longer setting times compared with conventional diesel cutbacks. Among the formulations, the 60% diesel-40% FAME blend provided the most balanced evaporation characteristics, while the 40% diesel-60% FAME blend achieved the highest shear strength, indicating enhanced bonding performance. Cost assessment revealed an 11.53% reduction in production costs, and environmental analysis showed a 27.4% decrease in greenhouse gas emissions and a 29% reduction in energy consumption relative to diesel-based cutbacks. Overall, the findings demonstrate that FAME offers a technically viable, economical, and sustainable alternative to diesel in cutback bitumen production, providing both performance and environmental benefits.