• CO2 mineralization curing of steel slag-fly ash-Portland cement ternary paste achieves significant CO2 uptake and improved mechanical performance, with residual water/cement ratio, CO2 pressure, curing time, and steel slag content as key interactive factors.
• Factor interactions become pronounced at higher steel slag dosages (>30%), lower residual water/cement ratios (0.1–0.15), and CO2 pressures of 0.1–0.3 MPa, all of which significantly influence compressive strength and CO2 uptake rate.
• Microstructural analysis reveals that mineralization chiefly yields CaCO3 and silica gel; post-curing reduces pores larger than 50 nm and increases harmless pores smaller than 20 nm, thereby refining the pore structure.
• Life cycle assessment demonstrates that CO2 mineralization curing of SS-FA-Portland cement solid waste concrete can substantially reduce environmental impacts, supporting low-carbon construction materials.