Long-Term Mechanical and Environmental Performance Monitoring of Steel Slags in Granular Roadways

Recent years have seen the use of steel slag in roadway applications. This is primarily driven by the growing emphasis on utilizing recycled materials to promote sustainable development. However, this widespread utilization also raises concerns related to long-term mechanical performance and environmental effects. This study evaluates the long-term mechanical and environmental performance of steel slag used in granular roadway layers over 7 years. The steel slag used in this study was electric arc furnace slag, sourced from two suppliers with different gradations (Types A and B). Both types were placed at two layer thicknesses (5.08 and 10.16 cm), and their in situ and laboratory properties were thoroughly analyzed. The field and laboratory tests included the dynamic cone penetrometer, light weight deflectometer, resilient modulus M R , permanent deformation, X-ray diffraction, pH, electrical conductivity, and elemental concentrations. The results indicate that both slag types exhibited increasing stiffness and strength because of ongoing hydration and carbonation processes, with steel slag Type A (coarser gradation) showing a higher M R compared with Type B. The results of the 5.08 cm steel slag surface layers were comparable with the 10.16 cm layers, emphasizing the potential for design optimization to mitigate environmental risks. The effects of field carbonation, to effectively stabilize toxic elements, were reflected in pH and metal concentration measurements in the surrounding soils. Although laboratory tests indicated higher pH and elemental release for steel slag aggregates, conditions in the laboratory were extreme, causing disruption of protective carbonate layers, compared with those observed in the field. Both steel slag types demonstrated mechanical characteristics comparable to natural aggregates, offering a sustainable alternative.