Double percolation in the electrical conduction in carbon fiber reinforced cement-based materials

Electrically conductive cement-based materials are important as multifunctional structural materials. Double percolation has been observed for the first time in the electrical conduction in carbon fiber cement-based materials. It involves fiber percolation and cement paste percolation. The fiber percolation threshold increases with increasing sand/cement ratio and ranges from 0.30 to 0.80 vol.% fibers in the paste portion. The cement paste percolation threshold is between 70 and 76 vol.% carbon fiber cement paste in the mortar. A sand volume fraction of 24% or less (i.e., a sand/cement ratio of 0.75 or less) and a fiber content of 0.80 vol.% (or more) of the paste portion are recommended for attaining high conductivity. The use of a higher sand/cement ratio requires a higher fiber content to attain the same level of conductivity. For a compromise between cost and conductivity, a sand/cement ratio of 0.75 and a fiber content of 0.80 vol.% of the paste portion (corresponding to 0.59 vol.% of the mortar) is attractive. At a fixed fiber volume fraction in the paste portion, the conductivity of the mortar decreases with increasing sand/cement ratio.