Effect of glass waste and sodium hydroxide concentration on fly ash-pyrophyllite based geopolymer composites: Microstructural investigations and performance optimization

The current study investigates the feasibility of crushed glass waste as a precursor in the synthesis of fly ash-pyrophyllite-based geopolymer. Hardened geopolymerized specimens at an early age were assessed in terms of microstructural and technological aspects. To do so, various microstructural characterizations (XRF, XRD, FTIR, SEM, TG-DTA), mechanical, and physical characterizations, as well as dielectric properties, were performed. The study explores the influence of factors such as NaOH concentration (up to 14 M) and glass waste content (up to 10 wt%). The results revealed the occurrence of geopolymerization and the emergence of new phases, particularly evident towards high concentrations and medium glass waste content. Notably, the optimal combination of properties was achieved with a sodium hydroxide concentration of 14 M and a glass waste content of 7.5 wt%. This specific formulation resulted in a remarkable enhancement in both mechanical and dielectric performance, yielding a compressive strength of 29.63 MPa and a relative permittivity of 1439, while maintaining a low dielectric loss of approximately 6. These findings underscore the potential of fly ash-pyrophyllite-glass waste geopolymers to serve as multifunctional materials, with applications spanning both mechanical and dielectric domains, thus broadening their utility in construction and advanced technological applications.