Effect of Water Content and MgO / ADP Ratio on the Properties of Magnesium Phosphate Cement

Materials such as magnesium phosphate cement (MPC) have attracted significant attention of researchers, therefore, understanding the effects of dosage parameters, such as water content and MgO/NH4H2PO4 ratio on phase formation is essential for obtaining cementitious matrices with improved performance. In the present work MgO was sintered at 900 °C and 1110 °C in a conventional oven, and the effect of water concentration and MgO/NH4H2PO4 (or ADP) ratio on the properties of MPC was evaluated in terms of phase formation by X-ray diffraction, pore size distribution, mechanical properties, and microstructure. For less-reactive MgO (calcined at 1100 °C) with a high MgO/ADP ratio, increased water content did not cause additional solubilization of ADP or formation of more hydrated phases, although the cement porosity increased. Compositions with more reactive MgO (calcined up to 900 °C) formed dittmarite (NH4MgPO4.H2O) independent of water content. Higher water content and MgO calcination temperature were associated with increased MPC setting time and decreased mechanical strength due to higher porosity.