Characterization of mechanical and electric properties of geopolymers synthesized using four locally available fly ashes

Geopolymer can be synthesized using industrial wastes such as fly ash, making it a promising material to replace Ordinary Portland Cement (OPC) as a green binder for concrete materials. One major barrier to prevent the wide application of geopolymer is that its properties heavily depend on the source materials. Aiming to evaluate the effect of fly ash on the properties of synthesized geopolymers, this study used four carefully selected fly ash to synthesize geopolymers. Comprehensive experimental programs have been carried out to characterize both the mechanical and electrical properties of these geopolymers. Mechanical testing shows that similar chemical composition in the source materials doesn't guarantee similar compressive strengths of the produced geopolymers, and that high content of calcium doesn't always lead to high compressive strength. Electrical characterization shows that both the magnitude of the electrical impedance and the electrical resistance of the geopolymers at early age measured at frequency of 10 kHz increase with the curing time. It has also been found that at the early age, the electric resistance of the geopolymers is mainly determined by the reaction rate. At the late age, this electric resistance is mainly controlled by the chemical composition. Measurements over one year show that the bulk electric resistances or the diameters of the high frequency arcs of all geopolymers increase with age during the one-year testing period, suggesting that the geopolymerization is a very long process.