Multiscale Evaluation of Mechanical Properties of Steel Slag Asphalt Mixtures

As an industrial waste, steel slag is widely used as a substitute for natural aggregates in road construction materials and other applications, due to the good physicochemical properties and low price. In this research, the mechanical properties and interface strength of steel slag asphalt mixtures (SSAMs) are investigated from a multiscale perspective. The experimental results show that the water stability increases with the increase of the addition amount of steel slag. When the dosage is 50%–100%, the residual stability of immersion of the original steel slag mixture increases by 1.2%–7.0%, while the residual stability of immersion of the natural aged steel slag mixture increases by 1.9%–10.5%. The freeze-thaw splitting test confirmed that due to the porous structure mitigation effect of steel slag and the chemical adhesion between metal cations and asphalt, the [tensile strength ratio (TSR)] value of the mixture was the highest at 100% content. The dynamic stability reaches the peak when the steel slag content is 50%, which increases by 3.4% (original steel slag) and 7.2% (natural aged steel slag) compared with the basalt mixture. The high-modulus minerals ( Fe 3 O 4 , CaO) in steel slag enhance the interfacial load transfer, while the density/hardness and strong interfacial bonding synergistically improve the strength and toughness. At a dosage of 30%–50%, the maximum indentation depth decreases by 3.87%–27.84%. Aging eliminates the risk of f-CaO expansion, and the optimal blending of 50%–70% steel slag significantly enhances the rutting resistance of heavy-duty pavements. The bottle rotation test confirms that the adhesion between steel slag and asphalt is markedly superior to that of basalt. After 48 h of water erosion, the asphalt stripping rate of steel slag is 16% lower than that of basalt. Furthermore, in contrast to the flake-like stripping observed on basalt, the stripping on the steel slag surface manifests as discrete pitting damage.