Electromagnetic Properties of Concrete and Their Significance in Nondestructive Testing

Abstract

Electromagnetic properties of hardened concrete specimens are measured over a microwave frequency range from 0.1 to 20 GHz. The experimentally obtained values provide information about the behavior of concrete and its interaction with electromagnetic waves. In addition to the frequency variation, the effect of different moisture contents on the electromagnetic properties is studied. Properties of mortar specimens and constituents of concrete, that is, coarse aggregates, sand, and cement, are also measured. An open-ended coaxial probe method is used for the measurement of real and imaginary parts of complex permittivity of concrete. The physical significance of the measured data in nondestructive testing, including penetration depth and detectability, is discussed. The results of electromagnetic property measurements indicate that the dielectric constant of dry concrete appears to be frequency independent over the range from 0.1 to 20 GHz, whereas the loss factor increases over that range. The moisture content of concrete significantly affects the dielectric constant and loss factor. The quantitative results obtained from this research will serve as a basis in applying wideband microwave imaging techniques for nondestructive testing of concrete using radar. The results can also be used for selecting the optimum combinations of radar measurement parameters for better detection.