• Steam-cured mortar with up to 15% molybdenum tailings powder achieves high early strength, reaching 85% of 28-day moisture-cured strength at 3 days and at least 90% of pure cement mortar at 28 days.
• The addition of 15% MTs significantly reduces harmful and more harmful pore proportions by 71.4% and 72.2%, respectively, and decreases most probable pore diameter from 12.7 nm to 10.8 nm.
• SEM analysis reveals that steam-cured paste with 15% MTs exhibits denser microstructure and more hydration products, attributed to the pozzolanic and filling effects of MTs.
• Molybdenum tailings powder serves as an effective alternative admixture to refine pore structure and enhance durability of steam-cured cementitious materials, promoting sustainable utilization of solid waste.