Enabling the Sustainable Utilization of Steel Slag in Asphalt Mixtures for Base and Surface Layers: Life Cycle Assessment and Environmental Benefits

Incorporating industrial by-products such as steel slag into pavement provides a sustainable solution to the depletion of natural aggregate. This study evaluates the environmental benefits of using steel slag in asphalt mixtures for surface and base layers in material production and construction stages of asphalt pavement through life cycle assessment (LCA) with the IMPACT World+ Midpoint method. The results demonstrate that adding steel slag reduces all impact categories in the production stage compared to control mixes. Specifically, ozone layer depletion is reduced by 46%, climate change is decreased by 335 t CO2 eq, and eutrophication potential is lowered by 30%. However, despite a 4%–25% increase in construction stage burden due to additional compaction and transportation energy, the total life cycle benefits of substituting steel slag for natural aggregates are driven by the production stage. In the material production and construction phases, the utilization of steel slag contributes to lower climate change emissions by 324 t CO2 eq, reduced ozone layer depletion of 42%, and decreased eutrophication potential by up to 27%. Furthermore, based on a multicriteria decision method employing entropy weight, the analytic hierarchy process, and the technique for order of preference by similarity to ideal solution, steel slag replacement ratios of 75% for surface layers and 50% for base layers are recommended. Finally, the robustness of the LCA results is validated through sensitivity and Monte Carlo analyses, confirming the study’s reliability. The findings provide quantitative evidence and decision-support framework to facilitate sustainable utilization of steel slag in road pavement.