Microstructure and strength development of fly ash-based geopolymer mortar: Role of nano-metakaolin

Abstract

Geopolymer mortar is a novel binder material that exhibits the same properties as of cement. However, being a waste material geopolymer binder has an edge over cement binder because of environmental safety. This paper elucidates the fluctuations in compressive strength and microstructure of fly ash based geopolymer mortar using 14 M molar concentrations of alkali activator solution along with different replacement levels of nano-metakaolin (0%, 2%, 4%, 6%, 8% and 10% of fly ash). The mixture of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) in the ratio of 1:2.5 was used as an alkaline activator solution. All the specimens were cured for 24 h temperature curing and tested after 3,7,14 and 28 days of ambient curing followed to temperature curing. Geopolymer mortar with 4% nano-metakaolin shows appreciable improvement in compressive strength at all curing ages. The phase composition and microstructure of fly ash based geopolymer incorporated with nano-metakaolin were investigated using scanning electron microscope (SEM) technique.