Influence of low-grade bauxite on the properties of magnesium phosphate cement

This article investigated the influence of low-grade bauxite (LG-bauxite) on the properties of magnesium phosphate cement (MPC), which were explored by testing the properties of the fresh mixture (fluidity, setting time, and temperature evolution), measuring the strengths, analyzing the hydrates and observing the microstructure. With the successive additions of LG-bauxite, the fluidity continued to increase to a value of 267 mm, and the setting time was prolonged from 13 min to 26 min. The use of LG-bauxite also improved the mechanical properties of hardened MPC samples, and the group containing 10% LG-bauxite yielded the highest compressive strength of 91.2 MPa at 28 days. In addition, by the technique of X-ray diffraction (XRD), thermogravimetric analysis (DTA-TGA), scanning electron microscopy (SEM) and backscattered electron image (BSE) equipped with energy dispersive spectrometer (EDS), the micro-analyses for the MPC pastes was carried out. The obtained results all confirmed the pore-filling effect of LG-bauxite in MPC system and illustrated the formation of new phases, which was thought to be the alumina phosphate hydrate and some aluminosilicate gels. The fresh MPC slurry blended with LG-bauxite exhibited a lower exothermic reaction intensity and a slower hardening stage, which showed that it could be used as a kind of quick repair material.