Fluidized bed combustion coal fly ash: comparative evaluation for potential use in alkali-activated binders

The physical, chemical, mineralogical and toxicity attributes of two fluidized bed combustion (FBC) coal fly ashes were evaluated, and were compared against that of a conventional coal fly ash. The potential use of the FBC ash in alkali-activated binders was also evaluated. Alkali-activated mortars were prepared and tested for compressive strength at different ages. The alkali-activated binders were also evaluated using SEM, TGA and FTIR methods. This investigation accounted for: (i) the differences in the combustion temperatures of FBC versus conventional methods of coal combustion; (ii) capture of sulfur from combustion emissions in the FBC method, and its incorporation into fly ash as crystalline solids; and (iii) the type and particle size of the sorbent used in the FBC process for capture of sulfur from combustion emissions. FBC ashes were found to differ from the conventional coal fly ash in terms of chemical composition, crystalline phases and carbon content. The higher crystallinity and carbon content and the larger particle size of FBC ashes were noted to challenge their potential use in alkali-activated binders. Suggestions are made based on the experimental results towards effective use of FBC ashes in alkali-activated binders.Abbreviations: FBC: Fluidized Bed Combustion; SEM: Scanning Electron Microscope; TGA: Thermogravimetric Analysis; DTA: Differential Thermal Analysis; XRF: X-Ray Fluorescence; XRD: X-Ray Diffraction; LOI: Loss-On-Ignition; TDS: Total Dissolved Solids; EPA: Environmental Protection AgencyI; CP-OES: inductively couple plasma spectroscopy; DI: Deionized; CFB: Circulating Fluidized Bed; ASTM: American Society for Testing and Materials