Comparative study on morphology of ground sub-bituminus FBC fly ash geopolymeric material

• FBC fly ash was ground to increase the surface area.
• Ground FBC fly ash was used as a source material in geopolymer.
• Different water glass to sodium hydroxide mass ratios were studied.
• Increase in water glass resulted in dense and homogeneous composites.
• Zeolites can be formed in composites.

Fluidized bed coal combustion (FBC) is a clean coal combustion and environmentally friendly process with low emission of SO2 and NOx to atmosphere. However, fly ash from FBC process is not suitable for further utilization due to the high sulfate and low glassy phase contents. FBC fly ash was ground to reduce pore and increase specific surface area for use as a source material in geopolymer. FBC fly ash geopolymers with different sodium silicate to sodium hydroxide (G/N) mass ratios were studied and characterized using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM–EDX), and Fourier transform infrared spectroscopic (FTIR) techniques. Compressive strength of materials was also tested. Test results indicated that G/N ratio had a significant effect on morphology and strength of geopolymer. Low G/N ratio gave low strength geopolymer with a large amount of calcium hydroxide. The high G/N ratio mixes with increased water glass content gave dense and homogeneous composites. The presence of a high amount of calcium resulted in the formation of calcium silicate products which coexisted with the sodium aluminosilicate products.

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