Influence of slag on water resistance of magnesium silicon potassium phosphate cement

Abstract

The poor water resistance of traditional magnesium phosphate cement (MPC) limits its wider application in engineering fields. So far, research on enhancing the water resistance of MPC has been relatively limited. Therefore, this paper optimizes the slag content based on magnesium silicon potassium phosphate cement to prepare slag-magnesium silicon potassium phosphate cement (S-MSPPC). The research results indicate that slag contains various active components, and its appropriate addition can refine the pore structure of the paste. With the increase in slag replacement rate, the paste setting time increases, and the fluidity decreases slightly. The hydration of silica fume to produce and ions significantly enhances the alkalinity of the paste and provides conditions for activating the activity of the slag. The S-MSPPC hardened paste can maintain alkalinity for the long term. Moreover, the water resistance of the S-MSPPC paste was significantly improved while ensuring mechanical properties. The water resistance coefficients of S-20 with 20% slag increased by 49.23% and 40.64% at 28 days and 56 days compared to the reference group S-0. This improvement was due to the participation of silica fume and slag in the hydration reaction to form M-S-H and C-(A)-S-H gels in the paste. These gel products fill the pores and microcracks in the paste, optimize the pore size distribution, reduce porosity, and enhance density. In addition, the alkaline environment within the paste effectively slows the dissolution rate of K-struvite in water, further enhancing the water resistance of S-MSPPC.