Improving the electrical conductivity of composites comprised of short conducting fibers in a nonconducting matrix: The addition of a nonconducting particulate filler

The addition of a second discontinuous filler (silica fume) that is essentially nonconducting to a composite with a comparably nonconducting matrix (cement) and a conducting discontinuous filler (carbon fibers) was found to increase the electrical conductivity of the composite when the conducting filler volume fraction was less than 3.2%. The maximum conducting filler volume fraction for the second filler to be effective was only 0.5% when the second filler was sand, which was much coarser than silica fume. The improved conductivity due to the presence of the second filler is due to the improved dispersion of the conducting filler. The silica fume addition did not affect the percolation threshold, but the sand addition increased the threshold.