Prediction of the electrical properties and shielding effectiveness of conductive concrete

This paper describes a procedure to estimate the shielding effectiveness of a concrete wall containing steel fibres. The conductive inclusions have a length that is much smaller than the wavelength in the concrete at the frequency of interest, and are arbitrarily oriented and uniformly dispersed in the concrete matrix in such a way that the composite material can be considered isotropic, homogeneous and with linear electrical properties. Its effective complex permittivity can be obtained, under the assumption of low concentration of the inclusions, from the spatial average of both the polarisation of the plain concrete and that due to the currents induced in the fibres by an impinging plane wave. The comparison of the calculated values of the effective complex permittivity with experimental data shows a good agreement. Once the effective complex permittivity has been found, the shielding effectiveness of a conductive concrete wall can then easily be calculated.