Microwave assisted cold consolidation of alkali activated suspension of glass waste powders

Abstract

Boro-alumino-silicate pharmaceutical glass has been considered as feedstock for several alkali activated materials. The present paper is intended to investigate the impact of microwave-assisted process on the hardening phase of alkali-activated materials, beyond the use of fine glass powders suspended in mild alkaline solution (2.5 M, KOH) and dried at only 40 °C. The results indicate a significant reduction in curing time, with interesting consequences on the hardening mechanism. Stable compacts are achieved through bridging of adjacent particles, in turn determined by condensation reactions at the surface hydrated layers, upon drying. Drying under microwave heating promotes the chemical stability of a gel phase, formed by reaction of glass components released in the activating solution. In fact, this process enhances the ‘trapping’ of alkali ions in hydrated carbonates. The application of microwave technology results in a reduction of depolymerization within the gel phase. Furthermore, it is observed that the mechanical compressive strength of the activated materials is notably improved when subjected to microwaved irradiation.