Electrical conductivity and compressive strength of carbon fiber reinforced fly ash geopolymeric composites

The effect of carbon fiber (CF) addition on the electrical behavior and mechanical property of fly ash geopolymer was investigated. The electrical resistivity of CF/geopolymer composites was systematically investigated as a function of CF concentration, liquid to ash ratio (L/A), curing temperature, aging time, measurement frequency, and measurement technique. Three different techniques used in this study for measuring electrical properties were I-V curve measurement, cyclic voltammetry, and electrochemical impedance spectroscopy. Each technique yielded similar results. The electrical conductivity was highly dependent on the CF concentration and percolation threshold. Below the threshold, the resistivity varied with curing temperature and time, but above that the resistivity decreased monotonically with respect to CF concentration irrespective of other factors. Changing the L/A shifted the percolation threshold to higher values, but the other electrical characteristics were similar. The composite with 0.5 wt% CF was found to exhibit the lowest resistance and highest compressive strength. Our findings showed that CF addition not only improved the electrical conductivity by several orders of magnitude, but also enhanced its mechanical property. The improvement of these properties was due to the combined effects as confirmed by X-ray diffraction and scanning electron microscopy techniques that the phases of matrix did not change and the fiber distribution was homogeneous and randomly oriented.