Investigation on the water resistance of the fly-ash modified magnesium phosphate cement

In order to improve the water resistance of magnesium phosphate cement (MPC), the flexural strength, compressive strength, strength retention rate and mass retention rate under different immersion conditions, were tested by XRD and SEM methods by adding 30%, 35%, 40%, 45% and 50% fly ash. The mechanism of fly ash improving the water resistance of magnesium phosphate cement was analyzed. The results show that when fly ash content is 35%, the mechanical properties of magnesium phosphate cement (MPC) reach the optimal, and the strength retention rate and mass retention rate are improved. Fly ash modified by magnesium phosphate cement produces no new hydration products. After it is soaked in water, a large number of flake like k-struvite are produced on the surface of MgO particles. Few cracks forms on the surface, which reduces the porosity and enhances the compactness, thus improving the water resistance of MPC cement.