The Effects of Bauxite Residue on the Alkali Silica Reaction in Cementitious Composites

Large scale use of bauxite residue (BR) in cementitious composites has been considered a promising alternative to reduce its landfilling. However, for BR to be considered for commercial use it is imperative to establish that the residue does not compromise the mechanical properties or the service life of structures. The excess alkalis conferred to BR by the Bayer process poses a potential risk to concrete as it could lead to alkali-silica reaction (ASR). To assess the ASR risk, an investigation was conducted in Portland cement (PC)-BR mortar mixtures at three levels of PC replacement (10%, 20%, and 30%). Also, three different Brazilian BRs were tested at a 20% PC replacement level. Results from the accelerated mortar bar test indicate a decreasing ASR expansion rate with increasing BR content, attributed to clinker dilution, despite the high sodium content. The study suggests that mechanisms such as the presence of soluble aluminates and portlandite consumption through pozzolanic reaction play a minor role on ASR expansion. Other possible mechanisms contributing to reduced ASR expansion could be shrinkage and the presence of zeolites in the form of sodalite, a major BR phase. These results contribute towards the safe use of BR as a supplementary cementitious material, potentially adding value to waste as a filler in the construction industry.