Development of Eco-Efficient Fly Ash–Based Alkali-Activated and Geopolymer Composites with Reduced Alkaline Activator Dosage

The eco-efficiency and economy of geopolymer composites largely depend on their alkaline activator dosage. In this study, the effect of applying a pre-setting pressure and variation of the aggregate-to-fly ash ratio on the alkaline solution dosage and mechanical strength of fly ash–based geopolymer composites was explored. It is shown that through control of the aggregate-to-ash ratio and application of pre-setting pressure, compressive strength could be increased by 102% and 86% for Class F fly ash–based geopolymer and alkali-activated Class C fly ash–based mixture, respectively. The total alkaline solution consumption could be reduced from 718 to $188\mathrm{kg}/{\mathrm{m}}^3$ and from 769 to $262\mathrm{kg}/{\mathrm{m}}^3$ for Class F fly ash–based geopolymer and alkali-activated Class C fly ash–based mixture, respectively. The proposed method reduced the alkaline solution consumption per compressive strength ($6.2\mathrm{kg}·{\mathrm{m}}^{-3}·{\mathrm{MPa}}^{-1}$) by up to 85% compared to that of the reference manually consolidated control geopolymer. The findings demonstrate that fly ash–based geopolymers could be made more sustainable and eco-efficient through tailored production techniques.