Optimization of factors affecting the silicate modulus of home-brewed sodium silicate (HBSS) solution from industrial & agro ashes

Abstract

This study investigates the development of geopolymer mortars using a greener alternative to commercial silicate can be produced. Home-brewed sodium silicate (HBSS) solutions were synthesized via a hydrothermal method using agro-industrial byproducts like rice husk ash (RHA) and palm oil fuel ash (POFA) as silica sources. These materials offer high silica content (approximately 90% for RHA and 60% for POFA) compared to traditional activators, potentially reducing reliance on energy-intensive commercial processes. The research explores the influence of various parameters on the silicate modulus (SM) of the HBSS solution, including NaOH solution molarity, stirring time, and thermal treatment of the ash materials. Geopolymer mortars were then formulated using GGBS/FA blend as the main binder and the HBSS solutions as activators. The results demonstrate that the optimal combination of NaOH concentration and stirring time for achieving maximum compressive strength depends on the ash source. Ground RHA achieved a maximum strength of 44.7 MPa with a 5M NaOH solution and 1 hour of stirring, while treated ground POFA reached a higher strength of 51.6 MPa using a 3M NaOH solution and 3 hours of stirring. The higher silica content and amorphous silica fraction in RHA likely contribute to the observed differences in optimal SM values between the ash sources. This research paves the way for utilizing waste materials and a greener activator production method for the development of strong and sustainable geopolymer mortars.