Effects of Hydrothermally Synthesized Xonotlite Produced from Red Mud on Some Mechanical Properties and Microstructure of Cement Mortars

Red mud (RM), an alkaline solid waste generated during alumina production, poses significant environmental challenges due to its massive accumulation. To address the accumulation issue and promote sustainable utilization, this study utilizes the calcium and silicon components in red mud. By adjusting the Ca/Si ratio to 1, xonotlite was synthesized via hydrothermal treatment at 200°C. Its performance as a cement additive was then evaluated. The results show that xonotlite outperforms raw red mud as an additive, significantly improving the 7-day compressive strength of cement mortar. At 28 days, its performance is comparable to that of the control sample. The optimal improvement was observed at a 2.5% dosage, with a slight enhancement in overall compressive strength. Scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) revealed that cement mortar with 2.5% modified RM (HT24) exhibited a denser microstructure. TGA further indicated a higher degree of hydration at 28 days. In conclusion, hydrothermally synthesized xonotlite from red mud, when used as an additive, reduces the environmental risks of red mud storage and provides a novel, environmentally friendly additive for construction and building materials.