Bauxite Residue as Supplementary Cementitious Material – Efforts to Reduce the Amount of Soluble Sodium

This study investigates the feasibility of using bauxite residue (BR) as supplementary cementitious material (SCM) for the cement and concrete industry. It is shown from pastes of BR and calcium hydroxide, that BR is highly pozzolanic in nature. The early hydration of cement pastes with BR is accelerated while long-term strength is reduced probably due to the alkaline nature of BR. To be used as cement replacement material in concrete, attempts have been made to reduce the alkali content of BR, in particular to reduce the chance of alkali-aggregate reactions. Co-calcination of BR with kaolin or washing and cooking of BR with calcium hydroxide or calcium hydroxide and gypsum resulted in considerable reduction of alkali content; up to 75%. At the same time the reactivity of the BR was reduced but still being higher compared to fly ash already used in the cement industry.