Preparation and curing method of red mud-calcium carbide slag synergistically activated fly ash-ground granulated blast furnace slag based eco-friendly geopolymer

The commercial alkali activators could account for more than 50% of the cost for producing geopolymers. Thus, to lower the carbon footprint of geopolymer by avoiding the utilization of energy-intensive commercial alkali activators, a novel eco-friendly geopolymer was synthesized from 100% solid wastes comprising red mud (RM), calcium carbide slag (CS), ground granulated blast furnace slag (GGBS) and fly ash (FA) in this study. Effects of GGBS contents and curing conditions on the compressive strength, fluidity and water requirement for normal consistency were investigated. The hydration products in the binders cured at different conditions were characterized by X-ray diffraction (XRD), thermogravimetric (TG), Fourier transformation infrared spectroscopy (FTIR) and scanning electronic microscopy (SEM). The results showed that GGBS improves the compressive strength as well as the mortar fluidity and reduces the water requirement for normal consistency of the geopolymer. Raising the curing temperature up to 60 °C and prolonging the heat curing duration to 12 h facilitate the dissolution and polymerisation of the FA-GGBS and therefore increase the amount of gel and crystalline products, whereas excessive heat-curing at temperatures higher than 60 °C and durations longer than 12 h causes shrinkage cracks at later age, which was detrimental to the compressive strength. The mineralogical characterization revealed that the amount of gel governs the strength development and heat curing favors the formation of secondary crystalline phase hydrotalcite. The developed binder can be used to produce low-carbon clinker-free concrete blocks to improve the sustainability of concrete industry.