Design of Geopolymeric Materials Based on Nanostructural Characterization and Modeling

摘要

Geopolymers, a class of largely X-ray amorphous aluminosilicate binder materials, have been studied extensively over the past several decades, but largely from an empirical standpoint. The primary aim of this investigation has been to apply a more science-based approach to the study of geopolymers, including introducing a variety of mathematical modelling techniques to the field. Si/Al ordering within the tetrahedral aluminosilicate gel framework is described by a statistical thermodynamic model, which provides an accurate representation of the distribution of Si and Al sites within the framework as well as physically reasonable values for the energy penalty for ordering violation. Direct measurement of the kinetics of the early stages of geopolymeric setting (up to 3 hours) is shown to be possible by energy- dispersive X-ray diffractometry (EDXRD), utilizing a high-intensity synchrotron X-ray source to conduct experiments in transmission geometry. Quantification of the results obtained by this technique provides a comparison between the setting rates of different geopolymer-forming systems, and shows clear trends with regard to temperature and Si/Al ratio as well as the nature of the alkali cation (or cation mixture) present. Finally, formulation of a reaction kinetic model for geopolymerisation draws together the results of the project. Based on an existing model for aluminosilicate weathering in aggressive media, the model includes description of dissolution, reorientation and reprecipitation processes including an autocatalytic polycondensation step, and can describe reactions involving either fly ash or metakaolin. Flexible stoichiometry of all polymerized species allows for variations in Si/Al ratios, and the effects of different alkali cations are also described. Model results are compared to calorimetric and EDXRD data, and predictions are consistent with the processes that have previously been postulated to occur during the early stages of geopolymerisation.