Automatic Detection of Reinforcement Rebar and Material Type Characterization in Concrete Slab Based on Frequency Analysis

Ground-Penetrating Radar (GPR) is an excellent tool to non-destructively detect the embedded rebar in concrete. Almost all civil engineering structures, including building, bridges and pavements, count with numerous rebar. The location and extraction of the position can be long and tedious. Several efforts were successfully carried out to automatically detect the rebar position in the time-domain. Here it is presented a new methodology to automatically detect the horizontal position of rebar through the frequency analysis - Fast Fourier Transform (FFT). The technique is quick and user-independent: it can be applied to the full A-scan, without selecting a specific time window. It was observed that both the amplitude and the integral of the FFT achieve maximum values when the wave intercepts the position of where a reinforcement rebar is located. The technique was tested in 2 cases, for rebar distributed with different spacing intervals and depth, several centre frequencies and both impulse radar and step frequency continuous wave GPR antennas. Apart of the rebar detection, the technique was able to distinguish between plastic and metal.