Effects of selected inorganic chemical activators on properties and hydration mechanism of high volume fly ash (HVFA) binders

Effects of Na2SO4, Na2CO3, and Na2SiO3 on setting time, compressive strength (up to 90 days), and hydration mechanism of binders with high volume (70 wt%, HVFA binders) of fly ash (FA) were investigated. Before chemical activation, FA was mechanically activated. Effects of the activators on hydration process were examined by isothermal calorimetry, X-ray diffraction and thermogravimetric analyses, and scanning electron microscopy. Pore solution analyses were also performed. It was found that, with addition of the chemical activators, Portland cement (PC) hydration was accelerated and the pozzolanic reaction started earlier, which resulted in shortening of setting time and increase in early compressive strength of the HVFA binders. Combination of mechanical activation of FA and the chemical activation by sodium silicate proved to be the best choice for synthesis of HVFA binder with good physicomechanical properties