Chemistry of Geopolymers

Abstract

This chapter focuses on how the aluminosilicate sources react with the alkaline activating solutions. The application of model systems based on metakaolin is explored in detail and a simplified geopolymerisation model is shown. The critical influence of water content on the outcome of geopolymerisation is clearly demonstrated. The wide range of analytical techniques employed to characterise the precursors and geopolymer microstructure is addressed. In the case of fly ash based geopolymers the interpretation of kinetic and mechanistic results is more difficult due to the presence of crystalline materials. Variation in fly ashes sourced from different plants also contributes to these difficulties. The alkali reactive glassy aluminosilicates may not be readily accessible for alkali dissolution reactions, being shielded by non-reactive phases. An alkali activation of fly ash model is described. The presence of soluble calcium entities changes the kinetics of fly ash geopolymerisation. It is shown that increasing CaO content generally increases compressive strength, reduces setting times and facilitates ambient curing.