Ground-penetrating radar signal modeling to assess concrete structures

To better understand reflected ground-penetrating radar (GPR) signals from sound concrete and delaminated concrete structures,five bare concrete slabs and nine slabs with simulated delaminations were constructed. Five concrete mixtures were used; till slabs were cast at 1.5 x 1.5 x 0.127 in. Delamination was simulated by placing polystyrene plastic pieces inside the slabs during casting. A method was developed to determine the complex dielectric constant of the five concrete mixtures. The effect of delamination was studied by comparing signals obtained from the bare concrete slabs with those obtained from the slabs with embedded polystyrene pieces. It was found that modeling the reflected signals using air average complex dielectric constant over the entire radar frequency range results in waveforms comparable to the measured ones. It was also found that reflections from air voids located at 50 mm from the surface overlap with the surface reflection. The distorted shape of the reflected signal, however, serves as an indication of the void presence.