Fresh and hardened properties of one-part fly ash-based geopolymer binders cured at room temperature: Effect of slag and alkali activators

Geopolymers are considered to be a sustainable and environmentally friendly replacement for ordinary Portland cement as they lead to a reduction in carbon footprint. The dosage and type of precursors and alkali activators have been known to be important parameters affecting the fresh and hardened properties of geopolymers. This study investigates the effect of slag content as well as type and dosage of alkali activators on one-part fly ash-based geopolymers cured at room temperature. Different ratios of fly ash were replaced with slag as a CaO-rich precursor. Setting time and flowability tests were carried out to evaluate the fresh properties, compressive and flexural strength experiments were conducted to determine the mechanical properties of the geopolymers. The mineralogy and microstructure of the samples were evaluated by Optical microscope, X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM-EDS) analysis. The experimental results revealed that the increase of slag content improved the strength and reduced workability. Moreover, some microcracks were observed when over 15% of fly ash was replaced with slag. In terms of activators, the sodium metasilicate anhydrous provided optimum strength and higher flowability compared to the others. Microstructural analysis results showed the presence of more unreacted particles when less than 8% Na ₂ SiO ₃ content as alkaline activator and also less than 15% slag as replacement was used in the system.