Sustainable Asphalt Mixtures Using Agricultural Waste Fillers: A Systematic Review of Rice Husk Ash, Bagasse Ash and Palm Shell Ash

Abstract The increasing demand for environmentally sustainable road infrastructure has led to a growing interest in replacing conventional mineral fillers in asphalt mixtures with agricultural waste-based alternatives. This systematic review examines the potential of rice husk ash (RHA), Bagasse Ash (BA), and Palm Shell Ash (PSA) as fillers in Asphalt Concrete – Binder Course (AC-BC) mixtures. A total of 72 peer reviewed studies published between 2010 and 2024 were analysed, focusing on key Marshall parameters: stability, flow, Void in Mix (VIM), Voids Filled with Bitumen (VFB), Voids in Mineral Aggregate (VMA) and Marshall Quotient (MQ). The review highlights that RHA and BA significantly improve stability and stiffness, with optimal performance typically at 6–8% and 4–6% filler content by weight, respectively. PSA, on the other hand, enhances flow and workability, performing best at 5–7% dosage. All three ashes demonstrate the potential to reduce VIM and VMA while increasing VFB, contributing to denser and more moisture resistant mixtures. However, the performance strongly depends on filler characteristics such as particle fineness, silica content, and carbon residue. Although these agro-waste fillers offer promising benefits in terms of sustainability and mechanical performance, challenges remain regarding standardization, processing, and field application. Further research is required to validate long-term durability and support large-scale implementation.