Percolation backbone structure analysis in electrically conductive carbon fiber reinforced cement composites

A simple model was presented to quantitatively calculate the backbone density of carbon fillers in carbon/cement composites. In this model, a “structure factor”, κ, defined as a function of the aspect ratio of the carbon filler, was first introduced to calculate the backbone density. To obtain the actual backbone density, carbon fiber (CF) reinforced cement composites with different CF concentrations were prepared and their DC electrical conductivities were measured. It was found that, when the CF concentration slightly exceeded the percolation threshold, the electrically conductive critical exponent was neither a universal value nor a constant that increases with the CF concentration. The results also indicated that the backbone density of the CF decreased with increasing CF concentration. The mechanisms of backbone structure evolution with increasing CF concentration were presented. The experimental results showed that near the percolation threshold the backbone density is approximately 0.15, which agrees well with the simulation results.