Modified bauxite residue blended cements – The effects of Na- and Al-rich pozzolans on phase assemblage and pore solution composition

Abstract

Several thermochemical treatments were developed to transform bauxite residues (BR) into reactive SCMs: co-calcination, vitrification and reductive smelting. This study investigates the impact of these treatments by comparing activated BR blended cements (10 to 50 wt.% SCM) obtained through different processes. The objectives are to: (1) evaluate the SCMs´ contribution to early-hydration, (2) understand the ”late-age” microstructure of BR-blended cements, (3) detect internal durability issues and (4) identify promising pathways to low-clinker BR-blended cements. QXRD, isothermal calorimetry, ICP-OES and other techniques were used to assess early and late age properties of blended systems. Results showed accelerated pozzolanic and clinker reactions in modified BR-blended cements, which were linked to the SCMs Na-bearing phases. At late-age, phase assemblages similar to kaolinite-rich LC³ cements are observed, despite C-A-S-H and AFm phases showing uncommon compositions.