Sonic inspection of concrete bridge decks

One technique for determining the integrity of concrete structures, such as bridge decks, involves dragging a chain across it and listening to the audible response. A distinctive, hollow sound is produced when a chain is dragged over a section of concrete containing a delamination. This technique has been automated by recording the sound produced by a dragging chain with a suitable microphone and processing these signals with a minicomputer to distinguish between ‘‘good’’ and ‘‘bad’’ sections of concrete. The equipment is mounted on a hand-pushed cart with chains attached so that they drag along the surface of the deck. In addition, the microphone is mounted in such a way, using standard noise control techniques, so that external noise is minimized. Traffic noise is filtered electronically. These improvements make the technique operator independent and allow inspections to be made in noisy environments. Another advantage is that this approach produces an objective record of the inspection, available both electronically and in hardcopy. These records can be compared to past and future inspections, allowing the inspectors to monitor the health of the structure. Results from bridge deck inspections will be presented, along with a description of the device and the signal processing techniques.