Comparative study on the effect of bauxite tailings on properties of magnesium-phosphate-cement-based materials before and after calcination

Abstract

To study the recycling of bauxite tailings (BT) and the poor water resistance of magnesium phosphate cement (MPC), the effects of BT and calcined BT (CBT) on the setting time, fluidity, drying shrinkage properties, compressive strength, and water resistance of MPC were investigated. The results showed that BT and CBT regulated the setting time and fluidity of MPC, adjusted the pH of the MPC paste, and decreased the generation rate of hydration products. The incorporation of BT decreased the early strength and increased the late strength of MPC, while the incorporation of CBT increased the MPC strength during the 28 d duration. Further, the optimal incorporation amount of BT and CBT was found to be 15 wt%. Although the water resistance of MPC was improved by blending BT or CBT, the effect of CBT was more significant, with a 32% reduction in compressive strength loss in the CBT groups compared to the control group for 28 d of curing. The alumina in BT was calcined and activated such that AlPO4 produced by secondary hydration reaction with phosphate enhanced the bonding of the solids and filled the pores and cracks of the MPC specimens, thereby increasing the densities of the specimens and improving their water resistance.