Performance Evaluation and Future Prospects of the Wastewater Sludge Ash as a Filler Material in Asphalt Mixture

Abstract This review examines the potential of wastewater sludge ash (WSA) as a sustainable filler in asphalt mixtures, with a focus on its mechanical performance, environmental safety, economic viability, and regulatory implications. Derived from the incineration of wastewater sludge, WSA is rich in inorganic compounds, such as silica and aluminium oxide, contributing to enhanced stiffness, durability, and resistance to rutting and cracking, outperforming conventional fillers such as limestone dust and fly ash. The fine particle size and high surface area of WSA improve aggregate packing and interlocking, leading to enhanced pavement performance. Additionally, this review evaluates heavy metal leaching risks and the compatibility of WSA use with regulatory frameworks. Economically, the WSA offers cost savings by reducing the need for virgin materials and minimising disposal costs. It provides a comparative analysis of WSA against other ash-based fillers and addresses key research gaps related to field validation and mix design optimisation. The findings support the WSA’s alignment with Sustainable Development Goals (SDGs) and national development plans (NDPs), positioning it as a viable material for circular and sustainable construction. Collaborative efforts among industry, academia, and regulators are essential for realising full implementation.