Characterization and Prediction of Clinker Phase Assemblage in Low-CO2 Iron-Rich Calcium Sulfo-Aluminate Cements Incorporating High Volumes of Bauxite Residue

Bauxite residue (BR) is the primary waste product of the alumina industry, with an annual production rate of 170 million tonnes, of which only 4 million tonnes are used productively. As a result, studies are being conducted to determine how high quantities of BR may be included in the manufacture of cementitious products. This research study proposed low-CO2 iron-rich calcium sulfoaluminate cement (CSA-F) by integrating more than 35 wt% BR as a raw material. Using thermochemical modeling, two set of cement clinkers were formulated from the raw materials consisting of limestone, gypsum, kaolin, and BR containing calcium oxide. The main reactive clinker phases targeted were calcium alumino-ferrites (C4AF) and belites (C2S) in the limestone-bauxite residue-kaolin system. However, some minor non-reactive phases such as gehlenite and perovskite were also formed when increasing the BR content in the mixture. Experimentally, a low-BR clinker (38 wt% BR) and a high-BR clinker (50 wt %BR) were produced at a temperature of 1250–1260 ℃, followed by fast cooling to stabilize the reactive phases such as the β-belite phase formed at lower temperatures and increase the hydraulic activity. Results obtained from the experimental characterization studies revealed that in the case of high-BR clinker, non-reactive phases such as gehlenite and perovskite were present, which may reduce the overall hydraulic activity of the clinker. Moreover, the solid solution of ferrite-phase formed in the high-BR clinker had a very low alumina-iron oxide ratio (A/F) which may correspond to low reactivity.