Damage Detection in Reinforcing Bars in Concrete Using Ultrasonic Waves

Reinforced concrete (RCC) is the most common form of civil engineering structures these days in which the steel bars are embedded in the concrete to improve the tensile strength. These bars deteriorate with time due to environmental action and excessive stresses and it remains unnoticed inside concrete. This degradation can be catastrophic if not detected at an early stage and can results in huge loss of life and property. Hence, it calls for a rigorous inspection and monitoring technique for the steel reinforcement and ultrasonic waves provide a potentially attractive solution. This study highlights the use of ultrasonic waves for damage detection in bars in air, which will be further extended to bar embedded in concrete. Minimum intrusion has been effected by exciting one end of the bar with an ultrasonic pulse and recording its propagation at the other end using the bar as a waveguide. Ultrasonic guided waves with frequencies in the range of 1-4 MHz were generated in healthy and damaged bars by varying the input frequencies of an ultrasonic transducer. Bar diameter of 12mm was used and damages were inflicted in the form of symmetrical area reduction in reinforcing bars. Two ultrasonic testing techniques, pulse echo and pulse transmission, were used to monitor healthy as well as damaged bars. Time of flight measurement in pulse echo indicated the damage location accurately. Amplitude of received signal in both pulse echo and pulse transmission was a measure of extent of damage. The two techniques when used in combination can predict the existence, location as well as the extent of damage in steel bars in air. The same methodology was then extended to steel bars embedded in concrete.