Towards the sustainable utilization of steel slag in asphalt pavements: A case study of moisture resistance and life cycle assessment

The large-scale promotion of steel slag (SS) in pavement construction remains challenging due to the concern of swelling potential. This study combined molecular dynamics simulations, surface free energy theory, and X-ray computed tomography to characterize the moisture damage resistance of asphalt mixtures incorporating SS. A case study of the life cycle assessment of SS asphalt pavement under different application strategies (two gradation types and three volume contents) was conducted, including global warming and human-related health impacts. The results indicate the higher polarity and abundant alkaline components of SS contribute to the bonding strength and tend to reduce the moisture susceptibility. The adhesion of steel slag to asphalt is 137.58%, 120.39% and 37.06% higher than that of granite, basalt, and limestone, respectively. The susceptibility index (Energy ratio) is reduced by 108.72%, 107.90% and 39.10%, respectively. Moreover, the incorporation of SS improves the compactness of the structure and delays the penetration and the interconnection between large voids. While the number of micro-voids increases geometrically after steel slag incorporation, ranging from 250% to 981% during FT cycles. The proliferation of microdefects has the potential to develop into macro cracks under a long-term freeze-thaw environment, meanwhile the risk of swelling-induced cracks is exacerbated with the high use of SS. The increased consumption of asphalt and transport mass of SS during mixture production are detrimental to the overall environmental impacts. However, the use of SS avoids the damage of exploitation and eliminates the huge risks of landfill accumulation. These two benefits are enormous and cannot be accurately estimated.