Multi-scale insights of recycling solid waste-based fillers into asphalt mastics: Surface adsorption configuration, microstructural morphology, and mechanical performances

The sustainable development of road engineering calls for innovative approaches to reduce reliance on natural mineral resources and address the growing challenge of industrial solid waste disposal. This paper systematically investigates the feasibility of recycling solid waste-based fillers in asphalt mastics through a multi-scale approach, using three kinds of mineral fillers for comparison. Molecular dynamics (MD) simulations were employed to elucidate the surface adsorption configurations and atomic-level interaction mechanisms between filler minerals and asphalt molecules. Complementary microscopic and macroscopic experiments were carried out to characterize the microstructural morphology and mechanical performance of asphalt mastics. The results reveal that asphalt molecules exhibit distinct distribution preferences on mineral surfaces, with resins, asphaltenes, saturates, and aromatics alternately dominating at varying distances from the filler surface. The incorporation of fillers, particularly those derived from solid waste, enhances the dispersion of polar components in asphalt and increases both surface roughness and adhesion force. Solid waste fillers, due to their complex microstructures, significantly improve the bonding area and interaction with asphalt, and may even induce chemical reactions not observed with traditional fillers. Compared to conventional mineral fillers, solid waste-based fillers—especially steel slag and iron tailings—demonstrate superior interaction with asphalt and markedly enhance high-temperature rutting, fatigue, and ductile fracture resistance. These findings are corroborated by MD simulations, which attribute the performance improvements to the preferential accumulation of resin and asphaltene components at the asphalt–solid waste filler interface. This study is expected to provide valuable insights for achieving carbon neutrality goals and the sustainable development of road engineering. © 2025 Elsevier B.V.