Effects of water purifying material waste on properties and hydration mechanism of magnesium phosphate cement-based grouting materials

In this paper, the effects of water purifying material waste (WP) as a mineral admixture on the setting time, fluidity, mechanical properties, water resistance, adhesive properties and hydration behavior of magnesium phosphate cement-based grouting materials (MPCG) are investigated. The results show that WP can delay the setting time, increase the fluidity, enhance mechanical properties and improve water resistance of MPCG. When the content of WP is 5.0 wt%, the fluidity of MPCG is the largest (281.5 mm), and the compressive strength at 28 d can reach 8.6 +/- 0.1 MPa, and the softening coefficient is larger than that of the control group (without WP). The analysis results of hydration heat show that WP can delay the early hydration reaction of MPCG, the total heat release of the MPCG system decreases. Microscopic analysis shows that the main hydration product of MPCG is K-struvite, and WP can improve the density of the microstructure, so that the bonding interface of MPCG with coal gangue substrate is tightly bonded, and there is no obvious crack between the bonding interfaces.