Effect of the alkali metal activator on the properties of fly ash-based geopolymers

The alkali and alkali earth metal cations present during the formation of m ost known aluminosilicate structures have a very significant effect on both the physical and chemical properties of the final product. Geopolymers are no exception, although this effect has not been thoroughly quantified and in the case of waste-based geopolymers it has not received any significant attention. The present study investigates the effect of mainly Na+ and K+ o n the physical and chemical properties of fly ash-based geopolymeric binder s both before and after setting has occurred. A variety of tests were condu cted, including rheological measurements, various leaching tests, compressi ve strength testing, specific surface area determinations, and infrared spe ctroscopy (IR). It is concluded that the alkali metal cation controls and a ffects almost all stages of geopolymerization, from the ordering of ions an d soluble species during the dissolution process to playing a structure-dir ecting role during gel hardening and eventual crystal formation.