Mechanical and microstructural dissimilarities in alkali-activation for six Class F Korean fly ashes

This study presents the preliminary investigation for the microstructural characteristics of the alkali-activated fly ashes, synthesized using six different Korean Class F fly ashes, to address the large mechanical strength differences between the activated ashes using compressive strength testing, XRF, XRD, and SEM/EDS (YAG BSE, SE and elemental mapping). The results show that although the original fly ashes are not much different in XRD and XRF data, the reaction products after activation were dissimilar between the activated ashes. Particularly, the activated sample containing Al-rich chabazite produced much higher compressive strength than the other samples with zeolite A–Na. The SEM/EDS results exhibit that the activated fly ashes tended to have the higher compressive strengths as the reaction products possessed the lower Si/Al ratios down to one.