John L. Provis, Peter Duxson, Grant C. Lukey, and Jannie S. J. van Deventer. Department of Chemical and Biomolecular Engineering, University of Melbourne, Parkville, Australia
Geopolymers are a class of X-ray amorphous alkali aluminosilicate gel binder materials with potential applications in a wide range of areas. In particular, geopolymers can provide significant improvements over traditional Portland cement technology in applications requiring resistance to acid or salt attack, or thermal stability at temperatures up to 1000°C. The quasi-zeolitic nature of some of the phases formed during geopolymerization is also of significant interest in immobilization of cationic waste streams. However, it is only recently that the structures and synthesis mechanisms of geopolymers have begun to be modeled. Nanostructural information has been obtained by MAS-NMR, microscopy and synchrotron pair distribution function analysis, which together have provided for the first time the ability to analyse both framework and non-framework cation sites and ordering within the geopolymer gel binder phase in detail. Comparison between the results of an empirical reaction kinetic model and data obtained by in situ energy dispersive synchrotron X-ray diffractometry is presented, and insight into the geopolymerization process and its influence on the microstructure of geopolymers is undertaken. The results presented will have significance in determining the performance of geopolymers in applications requiring controlled setting rates and rheology, or where long-term chemical stability is important.