The Effect of Ionic Contaminants on the Setting Behaviour of Geopolymeric Gels

Geopolymerisation is a new technology that processes and transforms aluminosilicate minerals into mechanically strong and chemically stable products. In this investigation, minerals such as fly ash and kaolinite were used as the solid raw materials for geopolymerisation. Inorganic salts were added to the geopolymeric pastes to simulate ionic contamination during processing for building and construction applications. The resultant products were examined and characterised physically. It was found that the early strength development of geopolymeric pastes could be changed according to the nature as well as the extent of the contamination. At a small dosage, the effect of the contamination on the early geopolymeric system depended heavily on the nature of the artificial surfaces that were created in the geopolymeric solution through the addition of the chemical additives. The samples demonstrated different yield stress development due to the different nature of the additive surfaces exposed to the geopolymeric solution. These results suggested that heterogeneous nucleation could be responsible for the change in rheological behaviour upon inorganic salt addition. The contamination did not show significant structural change according to XRD, but it influenced the compressive strength and setting processes of the geopolymer due to the unique interactions of the anions present.