Effect of Modified Magnesium Oxide on the Properties of Magnesium Phosphate Cement under a Negative Temperature...

As a rapid repair material, magnesium phosphate cement (MPC) can be used under various environmental temperature conditions, but different temperatures significantly impact its strength and working performance. In this study, based on the surface modification of magnesium oxide, the working and mechanical properties of samples were investigated at an ambient temperature of -5 °C, and the hydration properties and microstructure of MPC were investigated using X-ray diffraction (XRD), thermogravimetric analysis (TG), mercury-in-pressure (MIP), and scanning electron microscopy (SEM). The results show that the modified magnesium oxide at a negative temperature prolongs the setting time of MPC from 10 min to more than 30 min, and fluidity can still be maintained or increased after half an hour. From 1 d to 28 d, the compressive strength growth rate of the reference group was 257.0% compared to 723.8% for the 10 wt% water-glass-modified MgO sample. K-struvite transformed from a blocky growth to a needle-like growth with the modified sample filling the pores and cracks inside the matrix. Compared with the unmodified sample, MPC's porosity decreased from 9.62% to 9.23% for 10 wt% water-glass-modified MgO. Therefore, the surface modification of magnesium oxide not only prolonged the setting time but also further benefited mechanical performance, which provides the prerequisites for MPC construction in negative-temperature environments.