Characterization of Complex Dielectric Permittivity of Concrete by GPR Numerical Simulation and Spectral Analysis

In this paper, we present a numerical finite-difference time-domain (FDTD) simulation procedure developed to quantify the frequency-dependent ground penetrating radar (GPR) spectral responses occurring in four on-site scenarios involving concrete that is dry, half-saturated, saturated and chloride- contaminated. The responses are (1) numerically simulated by making use of the real and imaginary parts of complex permittivity derived from the GPR signal's two-way travel time and rebar reflection amplitude, respectively; then (2) characterized using Nyquist and Bode plots, and (3) compared to the wavelets obtained from authentic concrete specimens. The characterization shows good correspondence with the well-established Debye's models. Experimental validation shows that the simulated dispersion model is compatible with authentic concrete specimens when an optimal centre frequency is used. The method demonstrated in this paper can be used to convert GPR into a spectral analyser for predicting the on-site variability in material properties, the expected depth ranges of targets, and levels of attenuation and scattering before actual GPR survey.