How can a bridge deck be best evaluated to find the areas that have become delaminated?
The California Division of Highways uses a chain drag made of about four or five 18-inch-long segments of 1-inch link chain attached to a tee made of copper or aluminum tubing. The chain is attached to the 2-foot crossbar of the tee, which has a 2- or 3-foot stem used as a handle. The chain is dragged across the deck with a swinging motion to produce a ringing sound, which suddenly becomes dull when a delaminated area is encountered. The method has been found to be more reliable than tapping the surface with a hammer. For more sophisticated surveys requiring that the spread of delamination be monitored the Texas Highway Department uses an acoustic sounding device on a cart. It includes an oscillating solenoid that transmits 60 impacts per second to the deck through steel-rimmed wheels. The acoustic wave is received by microphones in another set of wheels and transmitted to a 2-channel pen recorder. It surveys about an 18-inch path.