Mineral-dependent interfacial adsorption and filler-ratio-dependent rheological trade-offs in copper-tailings asphalt mastics: experiments and molecular dynamics

Copper tailings (CT) are heterogeneous mineral residues, yet their effects in asphalt mastics are often interpreted as those of a chemically uniform filler. This study investigated the effects of mineral surface chemistry and filler-to-binder ratio (f/b = 0.5–2.0) using compositional, microstructural, rheological, and molecular-dynamics analyses. CT consisted mainly of SiO₂ (46.56 wt.%), Fe₂O₃ (23.06 wt.%), and Al₂O₃ (16.52 wt.%). FTIR indicated no new chemical bonds after blending, while SEM showed particle wetting and local particle-rich regions at f/b = 1.0. At f/b = 1.0, viscosity-temperature susceptibility decreased by 2.8%; at −24 °C, creep stiffness decreased by ~9% and m-value increased by ~13%, although stiffness remained above the 300 MPa criterion. The f/b = 1.5 mastic exhibited the most stable complex-modulus enhancement and phase-angle reduction. Increasing f/b to 2.0 reduced non-recoverable creep compliance by ~21–25% but caused anomalous behaviour near 50 °C. Simulations yielded Fe₂O₃ > Al₂O₃ > SiO₂ in binding energy. Overall, f/b = 1.0–1.5 is proposed as a candidate range for mixture-level validation rather than a universal optimum.