Behavior of magnesium phosphate cement with addition of sulphoaluminate cement at elevated temperatures

Magnesium phosphate cement (MPC) as repair materials of the structures or package materials for wastes may be exposed to elevated temperatures during fire attack. When MPC paste was exposed to about 1300 °C, a sharp increase in compressive strength was observed due to sintering. However, MPC exposed to elevated temperature, especially below 1000 °C showed a sharp decrease in compressive strength. Ye'elimite mineral in sulphoaluminate cement (CSA) has been proven to take part in the hydration of MPC and form some amorphous phases. The introduction of CSA in MPC could provide reactive Al and Si, which may be beneficial to improving the high temperature resistance of MPC. The present study aims to introduce CSA into MPC to improve its thermal properties at elevated temperatures. MPC pastes with pure dead burned MgO and various contents of CSA were prepared and exposed at elevated temperatures from 200 to 1100 °C. The compressive strengths, strength retention, dimensional changes, weight loss, phase changes, microstructures and open porosities of MPC pastes with CSA at elevated temperatures were studied. The proper addition of CSA in MPC pastes could form some new amorphous phases, reduce the open porosities, promote the sintering progress and enhance the strengths at elevated temperatures. To promote the properties of the MPC pastes at elevated temperatures, 10% and 30% CSA were recommended to replace dead burned MgO in MPC pastes at exposure temperatures above 1000 °C and below 400 °C, respectively.