Nondestructive Testing of Bridge Decks and Tunnel Linings Using Impulse-Response

This paper describes how the presence of poor bonding at interfaces between, asphalt, membranes and concrete on bridge decks or between the original concrete and repair patches of tunnel linings often causes a faster deterioration of the different materials, resulting in for example corrosion of the reinforcement, which can lead to spalling of the concrete cover layer. Visual inspections often only disclose these problems at a late state in the deterioration process and repair or replacement of portions or the whole structure can be expensive. Regular inspections combining visual and NDT tools, such as the impulse-response technique and verification of the results by drilling out a few cores, can disclose problems at an early state and provides valuable information of the actual condition of the structure. The use of the impulse-response technique gives the user an indication of the mobility and stiffness of the structures and hence a tool to evaluate the presence of conditions such as poor bonding or delaminations in the structure. Large areas can be tested rapidly and data are valuable for planning future strategies for maintenance or repair of a structure. This paper presents some typical case histories with emphasis on the advantages and limitations of the impulse-response technique.