Steel slag aggregate as a sustainable alternative to railway ballast: field and laboratory evaluation

Abstract

Sustainable construction practices are increasingly prioritized in civil engineering. In parallel, concerns about the depletion of natural aggregates have stimulated research into alternative materials, particularly for railway infrastructure. This study investigates the technical feasibility and environmental suitability of stabilized steel slag aggregate (SSA) as railway ballast, comparing its performance with conventional gneiss ballast. Comprehensive laboratory tests were performed, including particle size distribution, Los Angeles abrasion resistance, Treton impact resistance, X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS). Additionally, environmental assessments through leaching and solubilization tests were conducted to evaluate potential risks related to toxic metal mobilization. Continuous in situ monitoring of electrical resistivity from July 2022 to January 2025 was performed under actual railway operating conditions to assess compatibility with railway signaling systems. The results indicated that SSA exhibits superior mechanical properties, with significantly lower abrasion and impact indices compared to gneiss aggregate. Furthermore, the SSA displayed consistently higher electrical resistivity, with no interference detected in railway signaling circuits throughout the monitoring period. It is concluded that stabilized steel slag aggregate demonstrates technical and environmental advantages for railway ballast applications, providing a mechanically resilient and environmentally compliant alternative to conventional aggregates, particularly regarding mechanical strength, environmental safety, and compatibility with railway operations.