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.

矿物外加剂经常用于磷酸镁钾水泥 (MKPC) 体系中，以提高其性能并降低制备成本。本研究提出了一种在 MKPC 中再利用赤泥作为矿物混合物的新方法。采用响应面法优化赤泥改性MKPC的混合比例和力学性能，重点研究微观结构和反应机理。优化结果表明，最佳抗压强度镁磷质量比为2.7～3.1，赤泥含量为10～15%时可得。优化后样品的3 h、1 d和28 d抗压强度分别可以达到33.4 MPa、53.6 MPa和75.2 MPa。适量的赤泥还可以增加MKPC浆料的流动性，延长凝固时间。此外，MKPC 体系中赤泥的改性机理是通过物理填充效应（填充微裂缝和间隙以增加基质致密性）和化学效应（产生新的水化产物如磷酸钙以改善基体微观结构）。研究结果表明，赤泥的加入提高了MKPC的和易性和力学性能，降低了制备成本，使MKPC更好地作为一种新型建筑材料用于混凝土结构或建筑表面的修复和加固。