Water resistance and phase development of magnesium oxysulfate cement modified with roasted siderite tailings

In this study, roasted siderite tailings (RST) were used as a partial substitute for light-burned magnesia to investigate their effects on workability, setting behavior, mechanical performance, water resistance, phase evolution, and microstructure of MOSC. . Water-immersion results showed that 10% replacement was most effective, increasing the residual compressive strength after 28 d immersion by 30.3%. Phase and microstructural analyses revealed that the enhanced water resistance was mainly governed by the stabilization of the 5·1·7 phase and the reduced accumulation of weak Mg(OH)2. Reactive silicate species from the tailings participated in secondary hydration and formed water-stable M-S-H gel, which adhered to or surrounded the 5·1·7 crystals and inhibited their decomposition during immersion. These findings indicate that RST improves the water resistance of MOSC, providing a feasible route for the high-value utilization of siderite tailings in magnesium-based cementitious materials.