Detection of Multiple Flaws in Concrete Bridge Decks using Ultrasonic Wave Propagation

A current Nebraska Department of Roads (NDOR) project (M029) has successfully illustrated the ability of Ultrasonic Wave Propagation (UWP) to identify the onset of debonding between rebars and concrete such as it may occur as a result of corrosion effects. The principal investigators were able to detect significant changes in the attenuation measurements due to cracks smaller than 0.008 inch by monitoring the leaked energy of a guided wave travelling through the rebar, and demonstrated promise to identify its location along the embedded rebar. In the current study, the transmitting and receiving ultrasonic transducers are located on the rebar and in the concrete, respectively. This arrangement should theoretically allow for the assessment of the conditions of both materials (steel and concrete), as well as the bond between them, which would all influence the ultrasonic waves propagating from the transmitter to receivers differently. The benefit of this method as a monitoring tool is that, with earlier detection of problems, it is possible to employ lower cost maintenance options and extend the service life of bridge decks. The current study also demonstrated that there is a correlation between delamination widths and the amplitude (and velocity) of leaked energy, which is promising to develop this method into a diagnostic technique, in addition to being a powerful monitoring technique.