Effect of spherical silica fume and fly ash on the rheological property, fluidity, setting time, compressive strength, water resistance and drying shrinkage of magnesium ammonium phosphate cement

Due to the high bonding strength, Magnesium ammonium phosphate cement (MAPC) is suitable for the crack repair. However, the fast initial hydration rate, high viscosity and poor water resis-tance hinder its application in the crack repairing engineering. To solve the above problems, the spherical silica fume and fly ash were added into MAPC. The effects of spherical silica fume and fly ash on the rheological property, fluidity, setting time, compressive strength, water resistance and drying shrinkage of MAPC were studied. The results showed that both spherical silica fume and fly ash could reduce the plastic viscosity of MAPC and prolong the setting time. Spherical fly ash could improve the fluidity of MAPC. The late-age strength and water resistance of MAPC were increased and the drying shrinkage was reduced by adding spherical silica fume and fly ash. Therefore, it is concluded that the addition of spherical silica fume and fly ash into MAPC makes it more available to be applied in the crack repairing engineering.