Abstract:To address issues of high cost of traditional cement-based filling materials and poor bonding of ultra-fine tailings as a component, a solid-waste-based cementitious material was developed for the backfill of a molybdenum mine in Shaanxi Province. Steel slag, slag, and desulfurization gypsum were used as main raw materials, formulated with a performance modifier. The formulation of the solid-waste-based cementitious material was studied by varying the content and fineness of slag powder. The optimal formulation was selected to investigate application performance of backfill bodies and micromorphology of hydration products of the cementitious material. Results showed that the optimal formula of the solid-waste-based cementitious filling material was 60% slag powder (407 m2/kg), 20% steel slag powder, 20% desulfurization gypsum, and 0.6% performance regulator. Under this ratio, compressive strength of backfill bodies at all curing ages was superior to that of P·O 42.5 cement, with 28-day compressive strength reaching up to twice that of the cement group. Moreover, when cement-sand ratios were 1∶7, 1∶15, and 1∶16, respectively, strength requirements of different backfill zones were satisfied. Meanwhile, the material exhibited excellent fluidity and volume stability. Leaching toxicity indexes of all backfill bodies were lower than the limits specified in GB 8978—1996, indicating favorable environmental safety. Main hydration products were acicular-rod ettringite and fibrous gel-like C-S-H gel, which were interwoven to form a dense structure. The solid-waste-based cementitious filling material developed in this study had potentials of realizing resource utilization of solid waste and reducing backfill costs, providing technical support for green and efficient backfill of mines.