Location of reinforcement and moisture assessment in reinforced concrete with a double receiver GPR antenna

Abstract

Ground Penetrating Radar (GPR) is a popular technique in Civil Engineering for non-destructive investigations and more especially for the diagnosis of reinforced concrete structures. Its main applications are for the location of reinforcement and for measuring the thickness of elements. The advantage of GPR compared to other techniques, such as the use of a covermeter, is its rapidity of measurement, which allows large surfaces to be covered in a shorter time than with magnetic techniques. However, in a comparison with covermeters, the main disadvantage of GPR is the difficulty of accurately assessing the depth of reinforcement without advanced processing, or/and calibration.In this study, we propose a new methodology for GPR measurement and processing that allows accurate location of reinforcement in depth and an assessment of wave velocity inside the cover concrete at the same time. The new method of measurement employs a double offset configuration by using two bi-static antennas.A specific algorithm was developed for the determination of reinforcement depth and velocity inside cover concrete at the same time. The algorithm is tested on a 3 m × 3 m reinforced concrete slab with cover thickness ranging from 15 to 80 mm. With the algorithm, it is possible to measure the depth of reinforcement to within less than 2 mm, whatever concrete thickness.By using a calibration procedure specifically developed in this study, the velocity can be used to assess the water content inside cover concrete with a core conditioned at different moisture contents. A conversion model is obtained between water content and velocity measured by transmission, which can be used at different places in the structure to assess moisture.