The unusual solidification process of alkali activated slag and its relationship with the glass structure of the slag

Two types of blast furnace slags (HS N and HS V) with different CaO/SiO2 ratios, were activated by potassium silicate solution (M-s = 1). The results showed that most of the alkali silicate activated slag AAS mortars lost their workability within 10 min. Only an AAS mortar made from slag HS V had an outstanding fluidity even after 20 min. The microstructural evolution of the AAS pastes, as well as their selective dissolution residues after 1 h, were analyzed by an ultrasonic method, TGA, FTIR and solid state Si-29/Al-27 NMR. By employing a model developed for aluminosilicate glasses, Si(Q(n)(kAl)) species in the slags were calculated and fitted to their Si-29 NMR spectra. The results indicate that slag HS V experienced incongruent dissolution during hydration and that its dispersed glass structure in terms of Si(Q(n)(kAl)) abundance, was significant with respect to its unusual solidification process.