An XRD study of the effect of the SiO2/Na2O ratio on the alkali activation of fly ash

Soluble silica has a very significant effect on the microstructural and mechanical development of the cementitious materials produced as a result of the alkali activation of fly ash. In this study, four different alkaline solutions with different soluble silica contents were used to activate fly ash. The primary reaction product was a sodium aluminosilicate gel, while different types of zeolites appeared as minority phases. The percentage and composition of these reaction products were found to depend on both the soluble silica content present in the activating solutions and the thermal curing time. In addition, the amount of gel was observed to have a decisive effect on the mechanical strength developing in the material.