Influence of Si/Al Molar Ratio and Ca on Waste Glass Utilization in Fly Ash/Slag−Based Geopolymer Performance

Abstract

This study delved into the utilization of waste glass (WG) as a binder and fine aggregate in fly ash-slag (FS) based geopolymer concrete, by employing both ambient and oven curing methods. Ten distinct groups were examined: in five groups WG replaced fly ash at varying percentages (10, 20, 30, 40%), and in five groups WG was used as a sand substitute with different fly ash and slag ratios. The study used a new testing approach to investigate the leaching behavior of each material in the geopolymer. The results reveal an early-stage increase in compressive strength at 7 days of curing when incorporating Calcium (Ca) sources from slag. However, a slight reduction in strength was observed at higher WG content in the mixture. Leaching tests demonstrate that Ca readily leaches out and reacts in both ambient and oven curing, while Silica (Si) exhibits activity primarily in high-temperature environments. Microstructural examinations, conducted using scanning electron microscopy (SEM), confirm the development of compounds that contribute to strength, such as calcium silicate hydrate (C-S-H) and calcium aluminosilicate hydrate (C-A-S-H), which resulted in the formation of a dense microstructure.

Keywords: Geopolymer concrete, aggregates, waste glass cullet, leaching behaviours, Mechanical properties.