Reuse of red mud in magnesium potassium phosphate cement: Reaction mechanism and performance optimization

Abstract

Mineral admixtures have been frequently used in magnesium potassium phosphate cement (MKPC) system to improve its performance and reduce preparation cost. This study proposes a new method of reusing red mud as a mineral admixture in MKPC. The mixing proportions and mechanical properties red mud-modified MKPC were optimized by response surface methodology, with emphasis on the microstructure and reaction mechanism. The optimization results show that the best compressive strength can be obtained when the mass ratio of magnesium to phosphate is 2.7–3.1 and the content of red mud is 10–15%. The 3 h, 1 d and 28 d compressive strengths of the optimized samples can reach 33.4 MPa, 53.6 MPa and 75.2 MPa, respectively. The appropriate amount of red mud could also increase the fluidity and prolong the setting time of MKPC paste. In addition, the modification mechanism of red mud in the MKPC system occurs via physical filling effects (filling microcracks and gaps to increase matrix compactness) and chemical effects (generating new hydration products such as calcium phosphate to improve matrix microstructure). The research results show that the addition of red mud improves the workability and mechanical properties of MKPC and reduces the preparation cost, making MKPC better used as a new building material in the repair and reinforcement of concrete structures or building surfaces.