In order to determine the optimal proportion of magnesium phosphate cement-based binder (MPB), influences of setting adjusting agent, ratio of phosphate to magnesia, ratio of binder to sand, and addition of fly ash on the setting time and strength development of MPB paste and mortar was studied. The compatibility between MPB and traditional concrete and the hardening mechanism of MPB were also investigated. The results showed that the setting time of MPB can be regulated to 15～30 minutes by the addition of 10% of setting adjusting agent. When the ratio of phosphate to magnesia is 1∶2, MPB paste presents the best strength, with compressive strength greater than 40 MPa at 3 hours and 50 MPa at 1 day. When the ratio of MPB binder to sand is 1∶1.5, the MPB mortar reaches the highest strength, with compressive strength beyond 50 MPa and flexural strength more than 9.1 MPa at 3 hours. When the flowability of paste is kept the same, the addition of fly ash doesn’t reduce the strength of MPB paste and the color of MPB paste is changed to be very close to traditional concrete. The main reaction product of MPB is MgNH4PO4·6H2O. There is a good compatibility between MPB and traditional concrete, therefore MPB is very suitable for rapid repairing of concrete structures undergone natural disaster.
