Optimizing the utilization of bauxite tailings in low-carbon cement

Abstract

The disposal of bauxite tailings (BT) remains a significant challenge for the global aluminum industry. However, its application in Limestone Calcined Clay Cement (LC³) systems shows immense potential. Despite this, the optimal calcination temperature for BT and its effects on LC³ performance have yet to be clearly defined. To address this gap, the study employs thermogravimetric (TG) analysis, X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, R³ reactivity tests, hydration heat measurements, and backscattered electron (BSE) imaging to systematically investigate the relationship between calcination temperature, raw material properties, and LC³ performance. The results reveal that, in contrast to the conventional calcination temperature of 800 °C typically used for clay materials, calcining BT at 600 °C achieves complete dehydroxylation of kaolinite, while balancing amorphous content, degree of polymerization, and pozzolanic activity. Under these conditions, the 28-day compressive strength reaches 43.7 MPa, significantly exceeding that of samples calcined at other temperatures and the P·I 42.5-grade benchmark cement. This performance improvement is primarily attributed to a substantial increase in the content of C-(A)-S-H and AFm phases (Hc/Mc), along with more uniform hydration reactions and tighter particle bonding around unhydrated particles, resulting in a robust matrix structure. Based on these findings, future research should focus on the microstructural properties of the phases surrounding particles in LC³ systems incorporating low-grade clays. Such an approach could more efficiently and directly determine the optimal calcination temperature, minimizing reliance on indirect performance indicators. This study not only provides a scientific foundation for the application of bauxite tailings in LC³ systems but also offers new insights for promoting low-carbon cement in regions with limited clay resources, contributing to the sustainable development of both construction materials and the aluminum industry.