The fate of water in fly ash-based geopolymers

Researchers on geopolymers have proposed equations that hypothesised the process of geopolymerisation. In those equations, it appears that water gets to be generated during the final geopolymerisation process. Moreover, those equations suggest that there would be no water combined within the geopolymer itself. However, this hypothesis has not been proven and therefore it remains a hypothesis to be further researched. In this paper, the authors report their study on fly ash-based geopolymers which were activated using Na2CO3 and Ca(OH)2. The research included the determination of evaporable and combined water at the various steps of making the geopolymer. The composition and microstructure of the fly ash as well as the geopolymers were characterised in each step using scanning electron microscopy and X-ray Diffraction. The results obtained enabled accounting for the water used in the reactions. It is suggested that the resulting geopolymer compounds contain a measurable amount of non evaporable/combined water.

► Fly ash-based geopolymers were synthesized using Na2CO3 and Ca(OH)2 as activator.
► Evaporable and combined water were determined at various steps of making geopolymer.
► Composition of fly ash and geopolymers were characterised using SEM and XRD.
► Microstructure of fly ash and geopolymers were characterised using SEM and XRD.
► The geopolymer compounds contain a measurable amount of non-evaporable/combined water.