Alkaline Activation of Synthetic Gehlenite Glasses
Appears on pages(s):
alkaline activation; gehlenite glass; microstructure; paste; phase composition.
Alkaline activation of granulated blast furnace slags by highly concentrated solutions of sodium or potassium ions has been a subject of numerous investigations for many decades. Irrespectively of the type of activator used, the so-called C-S-H phase formed is very compact, of low C/S ratio, rich in sodium, aluminium and magnesium and is predominant hydration product. Properties of AAS pastes, mortars and concretes strongly depend on the chemical and phase composition of the slag. This paper presents the properties of the alkali activated pastes and mortars produced on the base of synthetic alumino-silicate glasses of gehlenite type. Setting time, mechanical properties and heat of hydration of the gehlenite-glass pastes are presented. Detailed studies of phase composition, microstructure and structure of alkali-activated gehlenite glasses are presented in the paper. Alkaline activation of gehlenite slag glasses is influenced by molar ratio Al2O3/SiO2 of the slag and concentration of NaOH. The hydration process is much quicker in the case of gehlenite type glasses than for typical industrial melilite granulated blast furnace slags. The results of XRD and SEM/EDS examinations show that in gehlenite type pastes amorphous C-A-S-H phase containing high amount of sodium, silicon and aluminium are the dominating hydration product.