Preparation and properties of magnesium phosphate cement with recycled magnesia from waste magnesia refractory bricks

Waste magnesia refractory bricks (WMRBs) are a high-quality magnesia resource with a MgO content of ＞80%. However, numerous WMRBs are not effectively utilized, leading to the waste of magnesia resources. WMRBs can be transformed into recycled magnesia (RM) with a MgO content of ＞82% by simply crushing and grinding the material. Using RM to prepare magnesium phosphate cement (MPC) can significantly cut the preparation cost of MPC and promote the efficient utilization of WMRBs. Herein, the chemical and mineral composition, hydration activity, and micro-morphology of RM are analyzed, and the physico-mechanical properties of MPC prepared with RM are studied. The results show that the chemical and mineral composition of RM is not significantly different from that of dead-burned magnesia (DM), but its hydration activity is remarkably lower than that of DM owing to the larger grain size of periclase and more regular particle morphology of RM. The setting time of MPC prepared with RM (MPCRM) increases significantly, and the hydration temperature rise decreases significantly, which is more conducive to the application of MPC to large-scale engineering. Although the early strength and long-term strength of MPCRM are lower than those of MPC prepared with DM, the 3 h compressive strength of MPCRM exceeds 25 MPa, while its 28-d compressive strength is close to 60 MPa; furthermore, MPCRM has a small drying shrinkage value and good water resistance, which can meet the requirements of repair construction.