Mechanochemically activated bottom ash-fly ash geopolymer

Abstract

A source of sub-bituminous coal bottom ash was mechanochemically activated by co-grinding fly ash and a sodium silicate powder for use in a geopolymer application. A total of nine different mixes were considered to study the effects of the mechanochemical treatment, mixing procedure, and bottom ash loading. The compressive strength, reactivity, rate of geo-polymerization and morphology were investigated using isothermal calorimetry, nano-indentation, optical and scanning electron microscopy, and Fourier-transform infrared spectroscopy. The solid-state mechanochemical activation attacks the fly and bottom ash particles producing small sheet-like activated agglomerates. The activation enhances the dispersion of the activated particle, alters the sodium silicate and aluminosilicate reaction kinetics and intensifies the interconnectivity of geopolymer structure, decreases pore size, and significantly increases compressive strength (between 60% and 80%). When treated in this manner, the bottom ash serves as an effective extender to fly ash in geopolymer systems up to 50% replacement of fly ash without significant reduction in mechanical strength or significant alteration to the microstructure.