Mechanical and hydration characteristics of autoclaved aerated concrete (AAC) containing iron-tailings: Effect of content and fineness

With the objective of reducing the negative impacts on environment and utilizing the secondary resource of tailings, the possibility of preparing AAC by using iron tailing was investigated. The bulk density and compressive strength were determined to indicating the feasibility of preparing AAC blocks from iron tailing. The morphology (FESEM-EDX), mineral constituent (XRD), thermal characteristics (TG-DSC) and crystal characteristics (29Si-NMR) of hydration products of AAC samples were analyzed to demonstrate the hydration characteristics of AAC products containing iron tailings effected by iron tailing content and fineness. The results indicated that the increasing content of iron tailing has negative effect on the mechanical property of AAC, and the finer of iron tailings can effectively enhance strength of AAC blocks. The main minerals in AAC products are C-S-H gel, tobermorite, anhydrite, hydrogarnet, and some residual minerals including quartz and calcite accompanied by ferric oxide and white mica in minor quantities. The increasing content of iron tailing obviously reduces the amount of calcium silicate hydrates; meanwhile, the finer of iron tailing accelerated the decomposition of white mica during the autoclaving process and has slight negative effect on crystallinity of tobermorite. It was also suggested that Al and Mg ions in iron tailings got into the structure of tobermorite during the hydrothermal reaction. This study provided the theoretical foundation for the utilizing of iron tailings in AAC production.