Sustainable optimisation of ternary geopolymer binders incorporating industrial by-products and a bio-based superplasticiser: A structure–performance approach

Multi-component geopolymer binders, including ultrafine industrial by-products, frequently exhibit poor workability and particle agglomeration, whereas typical petroleum-derived superplasticisers may be less compatible in highly alkaline environments. This research examined an organic additive (OA) derived from plant extracts as a bio-based superplasticiser for a ternary geopolymer binder comprising ground granulated blast-furnace slag (GGBS), red mud (RM), and silica fume (SF). The dosage of the alkali activator and the ratio of sodium silicate to sodium hydroxide were kept at 12% and 1.5, respectively, while the proportions of the precursor and the OA dosage were altered. The ideal reference binder included 65% GGBS, 30% RM, and 5% SF. The integration of OA gradually enhanced workability until it reached an ideal concentration of 20%, after which a slight decline was observed. At 28 days, the ideal OA-modified blend attained compressive, flexural, and splitting tensile strengths of 45.5, 6.1, and 4.2 MPa, respectively. Such results indicated enhancements of roughly 21.2%, 32.6%, and 27.3%, respectively, compared with the comparable mixture without OA. The findings from ultrasonic pulse velocity and rebound-hammer tests validated enhanced matrix consistency and internal integrity. At the optimal OA dosage, XRD, FTIR, and SEM measurements revealed increased aluminosilicate gel formation, improved matrix continuity, and decreased porosity. However, excessive OA integration marginally diminished strength, suggesting a preferable dosage limit. The results demonstrate that plant-derived OA improves dispersion, workability, and mechanical properties, facilitating the production of high-performance ternary geopolymer mortars from industrial byproducts.