Hydrothermal treatments of FBC waste aimed at obtaining ettringite-based building materials

Ettringite is a compound characterized by good binding properties, high water- and fire-resistance, and satisfactory mechanical strength. FBC by-products were investigated in order to assess their ability to produce lightweight building materials based on ettringite by hydrothermal treatment. Samples of FBC fly ash, FBC bottom ash and a blend consisting of 60% by mass of the former and 40% of the latter were paste hydrated, cured at 55°, 70°, 85°C for times ranging from 2 hours to 28 days and submitted to differential thermal analysis. FBC fly ash showed the best hydraulic behaviour. Ettringite tended to form early and to decompose later. Both phenomena were favored by increasing curing temperature and time: these parameters and the addition of blending components have to be carefully determined in order to enhance the selectivity of the reactants towards ettringite.