Define Reinforcing Steel - Limitations of Ultrasonic System?

The sound velocity measurement taken parallel to the reinforcing bars embedded in the concrete will be markedly higher because sound velocity in steel is 1.2 to 1.9 times the velocity in concrete. The effect is small while the axis of the rebar is perpendicular to the direction of sound propagation and the correction factors are of the order of only 1 to 4% depending on the quality of concrete. It is, therefore, recommended that sound trans- mission paths should be chosen, based on available drawings that avoid the influence of the rebar. If drawings are not available, rebar-mapping equipments may be used to verify the presence and orientation of embedded rebars.