Decreasing the electric permittivity of cement by graphite particle incorporation

Abstract

Cement containing graphite particles (admixture) was previously reported to exhibit attractive electromagnetic properties, which relate to the electric permittivity. The addition of graphite nanoplatelet (GNP, particles, 0.5% by mass of cement, ∼0.5 vol %) to cement containing silica fume (particles, 15% by mass of cement) decreases the relative permittivity (10 Hz–1 MHz) by ∼49% (unprecedentedly large fractional decrease among permittivity-affecting admixtures), decreasing from 33 to 17 (50 Hz), while affecting the resistivity negligibly. The decrease is attributed to the inhibition of the polarization-related charge carrier movement by the distributed GNP. The previously reported huge values of 108 at 10 Hz (Bhattacharya et al., 2008) and 103 at 50 Hz (Sachdev et al., 2015) of the relative permittivity of cement containing graphite particles are erroneous, due to the absence of an electrically insulating film between the specimen and either electrode during the capacitance measurement and the limitation of the impedance meter. The previously reported trend of the permittivity increasing with increasing graphite particle content (Bhattacharya et al., 2008) is opposite to the decreasing trend found in this work, and is also erroneous, as caused by the incorrectly high measured permittivity becoming even higher when the specimen is more conductive.