Recycling solid wastes into asphalt mastics for low-carbon pavements: Performance investigation and environmental impact assessment

Recycling solid wastes as fillers in asphalt mixtures offers a promising approach for developing low-carbon pavements. In alignment with this initiative, this study explored the feasibility of using five solid wastes with huge reserves in China, including steel slag, desulfurization gypsum, blast furnace slag, waste cement, and iron tailings, as fillers for paving bitumen. This study employed a combined approach of molecular dynamics (MD) simulations and experimental testing to clarify the performance advantages of solid waste-based fillers over mineral fillers in asphalt mastics and to elucidate the underlying atomic-scale mechanisms. To assess the environmental impact of using solid waste fillers instead of conventional mineral fillers in asphalt pavement, a life cycle assessment (LCA) was conducted. The results indicate that most solid waste-derived fillers provide superior performance in asphalt mastics compared to conventional mineral fillers, with improvements of 40 % or more in high-temperature rutting resistance and fatigue properties for most waste fillers, as well as enhanced interaction capacity and adhesion property. MD simulations reveal atomic-scale mechanisms underpinning performance enhancements: rock-forming minerals in solid waste fillers strengthen interfacial interactions with bitumen molecules, as evidenced by increased adhesion work and reduced diffusion coefficients. LCA results further demonstrate that the solid waste substitution technology systematically enhances critical environmental metrics across the lifecycle of pavement materials, with improvements in ecosystem quality exceeding 6 % and resource availability exceeding 9 %. The outcomes of this study establish a sustainable technical framework for green roads and provide a win-win strategy for solid waste management and mineral resource conservation.