Mix composition and characterisation of one-part geopolymers with different activators

Abstract

To improve the commercial viability of geopolymers, there is a need to develop one-part geopolymer mixes. In this research, 100% fly ash or a mixture of fly ash and slag was employed as the precursor. Meanwhile, the highly corrosive alkali solutions used as activators in conventional geopolymers were replaced by different solid activators (in powder form), such as sodium silicate, calcium hydroxide, sodium oxide, lithium hydroxide, potassium carbonate or their combinations. The mixes were subjected to both ambient and heat curing to check the influence of curing conditions. Effects of type/combination of the solid activators on the workability, early and final strength, hardened density and microstructure of these one-part geopolymer mixes were examined. The incorporation of slag in the binder increased the early and final strength of mixes but reduced the workability. Furthermore, the type/combination of solid alkaline activators affects the microstructure of the geopolymer gels and subsequently impacts the mechanical properties. Among the investigated ambient cured geopolymers, a relatively high compressive strength of 38 MPa at 28 days was obtained when the geopolymer precursor was composed of 50 wt% fly ash and 50 wt% slag activated by a combination of sodium silicate, calcium hydroxide and lithium hydroxide.