Use of fluidized bed combustion residues and alumina powder as components of ettringite-based aerated building elements

The use of industrial wastes and by-products for making construction materials unequivocally gives a pronounced environment-friendly character to their manufacturing process. Two binary (M1, M2) and one ternary (M3) mixtures, based on alumina powder, fluidized bed coal combustion fly- and/or bottom-ash were submitted to hydrothermal treatments in order to generate aerated building elements based on ettringite (6CaO·Al2O3·3SO3·32H2O); ettringite is a compound characterized by low density, water insolubility, high fire resistance and significant mechanical strength. The M1 – M3 systems were hydrated in a thermostatic bath (100 % R.H) at 55 °C and 70 °C for aging periods ranging from 2 h to 28 d; the hydrated samples were submitted to both differential thermal–thermogravimetric and X-ray diffraction analyses for assessing the formation of the hydration products. In this regard, the ettringite generation, being also dependent on the operating temperatures and times, was observed within all the investigated systems. Furthermore, the best results in terms of both ettringite concentration and formation rate were exhibited by the M2 system at 70 °C after 2 d of curing.