Hydration and chemical shrinkage of Portland cement with bauxite residue from Bayer process

Bauxite residue (BR) is a by-product from the aluminum industry, generated during the Bayer process to obtain alumina. It has valuable iron and alumina contents, with soluble ions that can interact with the cement compounds, which could make BR a new source of supplementary cementitious material. This work aims to determine the influence of different contents of BR in substitution to two types of Portland cement regarding the hydration reactions and chemical shrinkage during the first 48 h of hydration, as well as to monitor the crystalline phases with XRD and the amount of bound water and the hydrates formed with thermogravimetric analysis. The results show the interaction of BR and cement, with the formation of new products, such as N-A-S-H, C-A-S-H, aluminum silicate hydrate (AS), and calcium aluminate hydrate (CAH), that culminate in changes in the shrinkage as BR is added. It was also observed that BR accelerates and enhances the slag reactions due to its high alkalinity and soluble ions content and the fineness of the material added to the cement.