High-Temperature Properties of Magnesium Ammonium Phosphate Cement Modified with Gold Tailings

Magnesium ammonium phosphate cement (MAPC) exhibits rapid setting, high early strength, and potential resistance to elevated temperatures, making it a promising material for rapid repair and fire-resistant applications. Gold tailings (GT), which contain thermally stable Si- and Al-rich components, show potential for improving the high-temperature performance of MAPC. However, the mechanisms by which GT affects the residual performance and phase evolution of MAPC after exposure to elevated temperatures remain insufficiently understood. In this study, GT was used to replace the total binder in MAPC mortar at mass replacement levels of 0%, 10%, 20%, and 30%, while the MgO/NH4H2PO4 mass ratio in the remaining binder was kept constant. The effects of GT content on the workability of MAPC mortar, as well as its visual appearance, mechanical properties, mass loss rate, phase evolution, and microstructure after exposure to elevated temperatures, were investigated. The results showed that GT incorporation shortened the setting time and reduced the fluidity and room-temperature strength. After exposure to elevated temperatures, the GT-containing specimens exhibited higher strength retention and lower mass loss rates. After exposure to 1000 °C, the compressive strength of the specimen containing 30% GT reached 15.37 MPa, which was approximately 44.0% higher than that of the specimen without GT. Its flexural strength retention and mass loss rate were 47.42% and 9.84%, respectively. XRD and SEM results indicated that the formation of high-temperature residual phases, including Mg3(PO4)2, Mg2SiO4, and aluminosilicates, may contribute to the improvement of the residual matrix structure after exposure to elevated temperatures. Overall, GT incorporation improved the residual mechanical properties of MAPC after exposure to elevated temperatures, and the specimen containing 30% GT showed comparatively superior performance within the experimental scope of this study. These findings provide a reference for the resource utilization of GT in MAPC-based heat-resistant repair materials.