The influence of alkaline curing systems on the strength and microstructural properties of magnesium phosphate cement

Magnesium phosphate cement composites have been serviced under many alkaline environments in the numerous aspects of Civil Engineering. The study investigated the influence of alkaline solution with different pH values on the strength and microstructural properties of MPC hard pastes with the passages of time. The results indicated that the effects of alkali soaking are related to the molar ratio of magnesia to phosphate and pH value of the alkaline solution. The pH values can be divided into low-alkaline soaking (LAS, pH ≤ 10), moderate-alkaline soaking (MAS, 10 < pH ≤ 12), and high-alkaline soaking (HAS, pH = 14.0). It was observed that LAS and MAS have a slight influence on the early strength, and the permeation rate of low-alkaline solution is relatively slower. More importantly, compressive strength of the solid matrices decreased significantly in HAS solutions and the permeation rate of high-alkaline solution was very high. Moreover, curing media of LAS and MAS affects a little in the hydration products. Furthermore, high-alkaline environment triggered the higher porosity, coarser microstructure, and dissolving out of hydration products of MPC. The major findings of this study might be applied in the practical fields of MPC related activities.