Understanding the role of MgO fineness on the performance of magnesium phosphate cement through multi-scale study

This study investigated the impact of fineness of magnesium oxide (MgO) on the performance of magnesium phosphate cement (MPC) and analysis from the fresh and hardened properties of MPC. The fresh properties were determined by the setting time, fluidity, and early hydration heat evolution, the hardened properties were characterized by compressive strength and water resistance. The microstructure and hydration products were examined by XRD, TG-DTG and SEM. The results showed that a decrease in particle size of MgO resulted in reduction of the fluidity of MPC from 175 mm to 108 mm and shortening of setting time to 340 s and a continuously decrease in the exothermic reaction intensity. Finer MgO particles exhibit great influence on the later compressive strength of MPC paste and enhance the water resistance. The specimen with the smallest fineness of MgO yielded the highest compressive strength of 51.55 MPa at 28 days, which was pronouncedly improved by 35.41 % comparing to the controlled group. Besides, MgO with the particle size range of 20–60 μm is favorable to the late-stage compressive strength of MPC paste. Moreover, obtained results from the micro analysis showed that small size MgO promotes the formation of crystalline struvite and amorphous hydration products. The microstructure became more compact with less microcracks and defects as the fineness of MgO decreased.