The Ground Penetrating Radar is a device which can be used for non-destructive inspection of civil engineering structures such as reinforced concrete buildings and bridges. Because of its ability to detect defects and provide reliable image of the substructure, it has attracted large interest from both practitioners and researchers in the field of health monitoring of vital structures. The objective of this work is to analyze detectability of defects in reinforced concrete structures by considering the presence of a defect which can attenuate GPR signals. Defects embedded in the structure can in fact cause significant changes in the intensity of the hyperbolic like reflection patterns generated by reinforcement bars. To assess this effect, a numerical simulation study of GPR data was conducted by using the GprMax software which is based on finite differences time domain method. The proposed approach has enabled to study the modification affecting the radargram due to the presence of a defect of finite size.

The GPR is widely used for non-destructive evaluation of reinforced concrete structures. High resolution of detection is needed in order to differentiate between multiple targets present in the host medium. This article aims to numerically study the vertical and horizontal resolutions associated to detection of reinforcing bars buried in a structure made from concrete by means of GPR inspection. Use was made of open source software GprMax2D by considering the three work frequencies: 1GHz, 1.6GHz and 2GHz. The method of scanning is assumed to be according to B-scan protocol which was conducted along a profile traced on the surface of the inspected member. In situ measurements were made for a bridge pillar made of reinforced concrete by the MALÅ CX GPR system with a frequency centred on 1.6 GHz. The obtained results show that the GPR is effective in the examination of reinforced concrete structure and most of the steel bars can be detected. After making correction, the horizontal resolution predicted by a conventional formula was verified. However, the real vertical resolution imposes a minimum distance separating steel bars that is higher than that proposed in the literature. This is due to the high conductivity of steel bars that yields strong reflection of the signal at the first reached bars and which impedes significant secondary reflection from targets located below them.