This thesis investigates the competences, limitations, and modifications of a handheld ultrasonic tomography device for integration into a zero-intrusive automatic bridge maintenance device. The handheld device relies on low-frequency pulse-echo methodology to identify and localize a variety of defects as well as determine specimen thickness. Current available non-destructive equipment is not suitable for the evaluation of in-service concrete structures since it is time consuming and expensive. Therefore, there is a need to develop a high speed non-destructive testing device in order to evaluate current structures for retrofitting or new construction. This thesis validates this handheld device for integration, discusses preliminary design options, and identifies key features necessary for high speed application. Eleven preconstructed concrete slab specimens, containing a variety of artificial defects including delaminations, air-voids and water-voids, were tested using the handheld system. This research concludes that the system effectively determines the initial depth of the defects and rebar within 10 percent of the actual location, with the exception of one artificial delamination located an inch from the surface. This is the shallowest defect and indicates that there may be near-sighted issues. This device determined the thickness to be within 2.6 percent of the actual thickness for all specimens, ranging from 305 mm (12.0 in.) to 610 mm (24.0 in.) deep. It was also determined that transducer orientation plays a significant role in characterizing flaws; the vertical orientation is able to identify horizontal defects more clearly, while the horizontal orientation detects vertical defects more effectively. All flaws identified within the specimens are parallel to the surface, and cracks located at the surface or propagating vertically were not recognized by the system. It was also found that overlapping measurements significantly improve image clarity, but scans without overlapping measurements are still able to successfully characterize and localize an artificial defect as well as two layers of rebar. Slabs containing simulated delaminations demonstrate a shadowing effect, where whole or partial reflections of the plastic can be seen throughout the slab since the ultrasonic waves are unable to penetrate through the defect. The most functional design consists of a cylinder of transducers equally spaced along the outer surface area to eliminate signal timing issues and reduce damage from impact forces. The final product will be larger and able to operate at a variety of speeds since the signal will be generated automatically as the transducers come into contact with the specimen surface. Digital mapping is key for database application and should be integrated into the device to generate a visual map database of defects beneath the surface of concrete structures.
