ABSTRACT
ABSTRACT: NDT techniques such as impact-echo and impact acoustic available for the integrity assessment of concrete bridge can be employed to locate void, cracks, honeycombing, and delamination in concrete decks and slabs, as well as other concrete structure. These two methods have the similar theoretical background, i.e., both of them are performed by introducing a stress pulse impact source (such as a ball drop or hammer strike) at the surface of a structure and monitoring the stress waves with a transducer (impact-echo method) or microphone (impact acoustic method). Stress waves propagate into the structure and are reflected by the external surface and existing voids or delaminations, and thus to create a resonance condition which can be observed by a spectrum analysis of the acquired waveforms. The resonance frequency provides critical information about the structure geometry, soundness of the structure, and the acoustic behavior of interfaces between materials (Sansalone et al 1989; Sansalone et al 1997). One advantage of these two methods is that access to only one surface of a structure is needed, making them suitable for rapid assessment of structure.
