Utilization of steel slag as coarse aggregate and filler in stone mastic asphalt (SMA) mixture: Engineering performance, environmental impact and economic benefits analysis

The unquantified environmental impact and economic benefits of steel slag based asphalt mixture, as well as the difficulty in directly utilizing steel slag fine aggregate (SSFA) due to solidification, limit the utilization of steel slag in asphalt mixture. This research proposed an innovative method of using steel slag coarse aggregate (SSCA) and steel slag powder (SSP) filler prepared by grinding solidified SSFA to replace ordinary natural resources to prepare stone mastic asphalt (SMA) mixture. The feasibility of the proposed utilization method of steel slag was determined based on the analysis results of main engineering performance, environmental impact and economic benefits of steel slag SMA mixture (SSSM). The ordinary SMA mixture (OSM) was functioned as a control group. The investigated main engineering performance included fatigue performance, moisture stability, hightemperature deformation resistance and low -temperature crack resistance. Environmental impact was evaluated based on the life cycle assessment (LCA) method, and the relationship between the transportation distance of steel slag, common basalt and the emission characteristics was deeply analyzed. In addition, economic benefits were determined based on the cost calculation results. Results showed that SSSM was superior to OSM in terms of these main engineering performance. The emissions from SMA mixtures increased with the extension of transportation distance of steel slag or basalt. From the perspective of reducing emissions, choosing steel slag aggregate had advantages when the transportation distance was less than 365 km, otherwise, it was recommended to choose basalt. Under three different transportation distances (short, medium and long distance transportation), the introduction of steel slag in SMA mixture reduced the greenhouse gas emissions by 1.1% - 8.6%, of which the raw material production stage contributed the most. Furthermore, SSSM exhibited higher economic benefits, with a functional unit of SSSM pavement saving the cost by 14.4% - 19.8%. Therefore, using steel slag as a substitute for coarse aggregate and filler in SMA mixture can promote the reuse of solidified SSFA, reduce the environmental impact and total cost of all stages of constructing SMA pavement.