Bio-bitumen Technique for Eco-Friendly Management of Agricultural Waste: Advances, Current Status and Future Perspectives

Agricultural waste generation is increasing worldwide due to intensification of cropping systems, agro-processing expansion, and rising consumption. While residues such as rice husk, wheat straw, sugarcane bagasse, coconut shells/husks, palm oil biomass, and olive pomace are often valorized through combustion, composting, bioenergy, or bioproducts, large fractions still remain underutilized and may be openly burned or dumped, causing air pollution, greenhouse-gas (GHG) emissions, and soil and water impacts. In parallel, the road sector relies heavily on petroleum bitumen, and conventional asphalt mixtures consume large quantities of mineral filler and aggregates, contributing to resource depletion and embodied emissions. The “bitumen technique” for agricultural waste management—broadly defined as the incorporation of agricultural wastes (directly or after conversion to ash, biochar, lignin, bio-oil, fibers, or hybrid derivatives) into bituminous binders and asphalt mixtures—has emerged as an engineering pathway that couples residue management with infrastructure development. This review synthesizes advances in (i) agricultural waste ashes (e.g., rice husk ash, bagasse ash, palm oil fuel ash, wheat straw ash) as mineral fillers or binder modifiers; (ii) lignin-based and bio-bitumen approaches that partially substitute petroleum bitumen; (iii) biomass-derived bio-oils and bio-binders; (iv) biochar/nano-ash systems to improve rutting and aging resistance; and (v) composite strategies integrating waste plastics, rubber, and agricultural residues to optimize performance. The current status indicates that properly processed agricultural residues can enhance stiffness, rutting resistance, and in some cases durability—though low-temperature cracking, moisture susceptibility, heterogeneity, and long-term aging remain key concerns dependent on residue type, dosage, and processing route. Emerging life-cycle assessments suggest potential climate benefits for certain bio-bitumen pathways, but trade-offs (e.g., land use, sourcing, logistics) require careful governance. The review highlights practical protocols, characterization methods, mixture design considerations, performance trends, environmental and techno-economic implications, and research gaps. Finally, future perspectives are proposed for scalable deployment, including residue supply-chain certification, standardization, multi-objective mixture optimization, field trials in diverse climates, circular procurement, and integration with low-temperature asphalt technologies.