Microscopy and microanalysis of inorganic polymer cements. 2: the gel binder
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By scanning electron microscopy and microanalysis of fly ash-based and mixed fly ash-slag inorganic polymer cement (i.e., “fly ash geopolymer”) binders, a more detailed understanding of the gel structure and its formation mechanism have been developed. The binder is predominantly an aluminosilicate gel charge balanced by alkali metal cations, although it appears that calcium supplied by slag particles becomes relatively well dispersed throughout the gel. The gel itself is comprised of colloidal-sized, globular units closely bonded together at their surfaces. The microstructure of the binder resulting from hydroxide activation of fly ash is much less uniform than that which forms in a corresponding silicate-activated system; this can be rationalized in terms of a newly developed explanation for the differences in reaction mechanisms between these two systems. In hydroxide activation, the newly formed gel phase nucleates and grows outwards from the ash particle surfaces, whereas the high silica concentration in a silicate-activated system enables a more homogeneous gelation process to take place throughout the inter-particle volume.
KeywordsZeolite Geopolymer Nuclear Magnetic Resonance Spectroscopy Silicate Solution Potassium Silicate Solution
Partial financial support for this work was provided by the Australian Research Council (ARC), through Discovery Project grants awarded to J.S.J. van Deventer and through the Particulate Fluids Processing Centre, a Special Research Centre of the ARC.
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