Extended sustainability assessment of steel slag waste application in urban transportation infrastructure based on environmental impact and implementing feasibility

Steel slag (SS), a by-product of the steel-making process, can serve as an alternative to high-carbon aggregates in urban road construction, thereby reducing the ecological burden associated with its disposal. However, most existing studies have not considered the greenhouse gas (GHG) emissions impact arising from governmental promotion of this alternative, and they lack systematic sensitivity analyses, leaving the results insufficiently validated. This study utilizes a Life Cycle Greenhouse Gas Emissions Assessment model to derive the carbon labellings for various urban pavement materials. It then evaluates the net carbon benefits and feasibility of using SS substitutes in China's future urban transport infrastructure, within the context of current urbanization trends and relevant policies. Additionally, an embedded uncertainty analysis module is used to verify the reliability of the results. The findings indicate that while replacing natural aggregates in urban road pavements with SS leads to an increase in actual GHG emissions by approximately 3.11-4.97 kgCO₂e·m², it also generates additional carbon sequestration of 2.49-5.27 kgCO₂e·m², alongside recycling benefits of 10.40-15.99 kgCO₂e·m². Furthermore, when the proportion of SS pavements in urban reaches 80%, it enables urban road construction to achieve net-zero emissions, thereby transforming the potential threat posed by urbanization to the global climate system into an effective solution for mitigating climate change.