Towards the application of pretreated steel slag in asphalt pavements: A study on feasibility and mitigation strategies for volume expansion risk

To enhance the volume stability and mechanical properties of steel slag asphalt mixture (SSAM), this study employed four pretreatment agents—acetic acid (AA), oxalic acid (OA), silane coupling agent (SCA), and polyvinyl alcohol (PVA)—on steel slag (SS). The raw materials were first evaluated for basic physical properties, and the effects of different pretreatments on chemical composition and microstructure were analyzed using X-ray f luorescence (XRF) and scanning electron microscopy (SEM). Mechanical performance of SSAM with 60 % SS content was assessed, including high-temperature stability, low-temperature cracking resistance, and moisture resistance properties. Volume stability under various pretreatment conditions was also systematically investigated. Furthermore, the economic viability of different treatment methods was also incorporated into the scope of the study. At last, the Gray Target Decision (GTD) technique was applied to conduct a comprehensive evaluation of the long-term performance of SSAM under different pretreatment methods, integrating multidimensional performance indicators into a unified decision framework. Results indicated that AA and OA improved volume stability and adhesion via chemical reactions with active components on SS surfaces, while SCA and PVA formed hydrophobic films to inhibit moisture intrusion. The SCA-treated SSAM possesses superior comprehensive mechanical properties and volume stability, characterized by a volume expansion rate of merely 0.68 % — well under the 1.5 % benchmark. However, the inherent thermal instability of PVA induces a 7 % degradation in high-temperature performance. Based on the evaluation using the GTD methodology, it was further confirmed that the SCA-treated SSAM exhibited the most balanced and desirable long-term performance characteristics among all tested variants. In summary, the pretreatment approach not only effectively improves the applicability of SS in asphalt mixture formulations but also facilitates and promotes its sustainable resource utilization in practical engineering applications. © 2025 Elsevier Ltd.