Potential to Design Magnesium Potassium Phosphate Cement Paste Based on an Optimal Magnesia-to-Phosphate Ratio

Magnesium potassium phosphate cement (MKPC) is an important engineering material, and it has been attracting increasing attention. Properties of MKPC based materials depend largely on the magnesia-to-phosphate molar ratio (M/P) and the water-to-cement mass ratio (W/C). While the effect of W/C has been clear, experimental results of the effect of M/P in the literature seem to be inconsistent. In this paper, a model is developed to unify these experimental findings. The model hypothesizes that the strength of MKPC based materials is dominated by the volume ratio of magnesium potassium phosphate hexahydrate and space (MKP/space ratio), and the ultimate MKP/space ratio can be limited by the availabilities of the three reactants, i.e. magnesia, phosphate and water. It proves that, if the W/C of MKPC-based material is kept constant, there exists an optimal M/P that results in the highest compressive strength. It appears that the higher the W/C is, the smaller this optimal M/P will be