Waste glass in the geopolymer preparation. Mechanical and microstructural characterisation

Alkali activated materials have a variety of niche applications (other than as a large-scale civil infrastructure material) in which alkali-activated binders and concretes have shown potential for commercial-scale development. The majority of these applications have not yet seen large-scale alkali activated materials utilisation, moreover, there have been at least pilot-scale or demonstration projects in different areas and each provides scope for future development and potentially profitable advances in science and technology. This paper explores the feasibility of generating geopolymers from fly ash using waste glass as an alkaline activator (waterglass family). The mechanical properties of the cementitious geopolymers obtained by alkali-activating fly ash with three solutions: sodium hydroxide 8 M, sodium hydroxide 10 M + 15% waterglass and sodium hydroxide 10 M + 15 g of waste glass were determined, along with their microstructural characteristics using Fourier Transform Infrared Spectroscopy, X-Ray Diffraction, Mercury Intrusion Porosimetry, Mass Nuclear Magnetic Resonance, Scanning Electron Microscopy and Back Scattering Electron Microscopy. The main reaction product in all the systems studied was the alkaline aluminosilicate hydrate gel to which geopolymers owe their mechanical properties. The gel formed when the system contained an extra source of silicon was shown to prompt compositional differences, while the degree of reaction, microstructure and Si/Al and Na/Al ratios were very similar in the former two systems. Waste glass proved to be an effective alkaline activator in geopolymer preparation.