Sustainable magnesium phosphate cement with co-mechanically activated low-grade MgO and coal fly ash for sub-zero Arctic infrastructure

This study investigates magnesium phosphate cement (MPC) mortars incorporating low-grade MgO (LM) and coal fly ash (FA) subjected to co-mechanical activation for use under sub-zero temperatures (down to –34 °C) typical of field conditions in cold regions. The samples were tested for flowability, setting time, compressive strength, and hydration heat, while the phase composition and microstructure were analyzed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results show that co-mechanical activation enhances the reactivity of LM and FA, promotes K-struvite formation, and refines the microstructure, leading to higher compressive strength compared with the non-activated system under both room and sub-zero curing conditions. The proposed approach enables the use of low-grade MgO in MPC mortars for Arctic and cold-region applications.