The effects of borax on the setting time, compressive strength, bond strength, drying shrinkage and pH value were investigated for potassium magnesium phosphate cement (MKPC). The results show that with the increase of borax dosage, the setting time is gradually extended, both compressive strength and bond strength are greatly decreased, the drying shrinkage rate is increased. Especially high dosage of borax, the extension of setting time is more obvious. Compared with that without borax, when the dosage of borax is 12.5%, setting time can be prolonged by 214.8%.The influence of borax dosage on the time-dependent effect of compressive strength shows that when the dosage of borax is 2.5%~5.0%, compressive strength increases rapidly from 4h to 1d, and increases relatively slowly from 1d to 3d. When borax dosage is less than 2.5% or higher than 5%, the law of time-dependent effect of compressive strength is the opposite. Compared to borax prior to magnesia addition, the pH value of the system is larger and the time of inflection point is advanced when borax and magnesia are mixed together at the same time. The increase of borax dosage can reduce the pH value of the system, and decrease the rising rate of pH value, at the same time the required time when the final pH value is relatively stable is longer.

The effects of the ratio of magnesium to phosphorus (Mg/P) on the compressive strength, bond strength, drying shrinkage and pH value of magnesium phosphate cement (MPC) were investigated. The results show that the consistent effect of the ratio of Mg/P on compressive strength and bond strength, as the ratio increases, the strengths are both first increased and then decreased, and the best ratio is 3:1. For setting time and drying shrinkage, the effects of the ratio of Mg/P are both obvious. Mainly manifested as the increase of the ratio, all of them show a decreasing trend. And the setting time can be shortened by 78%, furthermore, 28d the maximum drying shrinkage rate can be reduced by 29%. The effect of the ratio of Mg/P on pH value is mainly that when the ratio increases, the time of the inflection point of pH value is obviously advanced, and their final pH value is close.

Because the setting time of magnesium phosphate cement (MPC) was too quick, its further application was restricted. Influence factors about magnesium phosphate cement setting time are summarized and the influence laws are studied in the paper. The results show that with the increase of phosphorus to magnesium ratio (P/Mg) or boron to magnesium ratio (B/Mg), the setting time is both obviously prolonged. The effect of water to binder ratio (W/C) on the setting time of MPC has an optimal point. As the specific surface area increases gradually, the setting time of MPC is greatly shortened. Although fly ash has effect on setting time of MPC, the effect is very small. At the same time, the setting time is closely related with environmental temperature, the pH value of the system and mixing volume.