Synthesis and characterisation of geopolymers from GGBS activated by diatomaceous earth and rice husk ash

Abstract

The two silica sources used to synthesise activating solutions for alkali-activating ground granulated blast-furnace slag (GGBS) were agricultural by-product rice husk ash (RHA) and naturally occurring sedimentary rock diatomaceous earth (DE), both rich in amorphous silica. Geopolymers were fabricated using a 10 M NaOH-based activating solution with RHA and DE at 0%, 5%, 10%, and 15%. Mechanical and durability properties were assessed through compressive strength, density, water absorption, and porosity testing, while microstructural examinations employed XRD, FTIR, and FESEM-EDS analyses. Results confirm that RHA and DE can independently substitute commercial sodium silicate as efficient silica sources, with optimal performance at 5% addition for both materials. The optimised mixes exhibited superior binder formation with the presence of amorphous calcium-alumino-silicate hydrate (C-A-S-H) gels and hydrotalcite-like phases, indicative of efficient alkali activation. The optimised mix with DE achieved a compressive strength of 34.85 MPa and a bulk density of 1.91 g/cm³, while the RHA mix achieved 27.05 MPa and 1.92 g/cm³, respectively. This study confirms the feasibility of using RHA and DE as alternative silica sources in geopolymer production, reducing costs and environmental impacts by lowering CO₂ emissions and eliminating the need for high-energy sodium silicate.