Driving Energy of Reinforcing Steel Bar for Discriminating Background Medium of Concrete

A method for discriminating the background media of concrete using the quality factor of elastic waves multireflected in the concrete was proposed. A reinforcing steel bar buried inside the concrete is employed as a sound source driven by the induction of impact electromagnetic field radiated from a spiral coil placed on the surface of the concrete. In this paper, the appropriate energy for driving the reinforcing steel bar, to obtain stable quality factors with clear differences between different background media, is studied experimentally. With various driving energies, multireflected elastic waves corresponding to three types of background medium, air, sand, and water, are measured. The quality factors are calculated by the linear predicitve coefficient analysis method. The results show that the quality factors tend to increase when the driving energy is at its lower region, and they remain comparatively stable when the driving energy is higher than a certain value. For reinforcing steel bars with different diameters, the curves of quality factors versus driving energies agree well by introducing a newly defined volume-normalized driving energy. For the reinforcing steel bar of 13 mm diameter, the appropriate driving energy for background media discrimination is approximately 0.5 J.