Anuoluwapo Sola Kolade, Bolanle Deborah Ikotun, D.O. Oyejobi
Sodium silicate is a primary activator in geopolymerization and is commercially produced through high-temperature and energy-intensive processes that contribute substantially to cost and environmental impact. This study presents a sustainable alternative by synthesizing sodium silicate from waste glass powder, aligning with circular economy principles. The novelty of this work lies in systematically evaluating how fusion temperature (500–650℃) and duration (2–3 hours) affect the phase structure, solubility and reactivity of waste glass-derived sodium silicate, and in directly benchmarking its performance against commercial sodium silicate in geopolymer mortars—an aspect rarely addressed in previous studies. The synthesized sodium silicates were characterized using pH measurement, X-ray diffraction, X-ray fluorescence, scanning electron microscopy and energy-dispersive X-ray spectroscopy. They were combined with sodium hydroxide to activate binary geopolymer mortars containing fly ash and slag. Mortars were thermally cured at 80℃ for 24 hours, followed by ambient curing and tested for compressive and flexural strength at 7 and 28 days. Fusion at 500℃ for 3 hours produced predominantly amorphous and highly soluble sodium silicate, yielding 28-day compressive and flexural strengths of 35.32 MPa and 7.38 MPa, respectively. Higher fusion temperatures increased crystallinity, which reduced solubility, reactivity, and strength. While waste-derived sodium silicate achieved approximately 25% lower compressive strength than commercial sodium silicate, it enhanced flexural strength by up to 26%. These findings demonstrate that optimizing fusion conditions enables waste glass to be valorized into an effective, eco-friendly activator, suitable for sustainable non-structural and semi-structural applications in geopolymer binder systems.