Stability of acid volcanic glasses in alkaline solutions: Understanding their potential to participate in the alkali-silica reaction

Experimental laboratory tests were performed using volcanic glasses from Argentina of variable chemical composition and texture, in 1 N KOH, NaOH, Ca(OH)2 and combined NaOH + KOH + Ca(OH)2 solutions, at 40 degrees C and up to 10 weeks. The initial materials were characterized by petrography, chemical analysis, XRD, FTIR and DSC-TGA. The reaction progress was evaluated by XRD, and the final products studied by SEM-EDS. The reactivity of the most reactive glass is attributed to a combination of its high porosity/permeability and alteration degree (indirectly assessed by the volatile mass loss up to ~250 degrees C). The glass silica content and Ca/(Al+Si) ratio could be other factors affecting the glass reactivity; however, more studies are needed to understand the influence of these variables.