Air-coupled acoustic sensing opens opportunities to dramatically increase the speed of data collection. The evaluation of feasibility of air-coupled sensing led to the development and implementation of a prototype air-coupled ultrasonic system (ACUS) for simultaneous collection of impact-echo and surface wave data in concrete bridge decks. The basic sensor unit of ACUS is a hexagonal air-coupled sensor array, which includes a solenoid-driven impact source at the center and six air-coupled sensors (ACSs) with parabolic acoustic reflectors (PARs) at vertices of the hexagon. Primary interests of air-coupled acoustic testing are related to detection of delamination using impact echo (IE), and measurement of concrete modulus and evaluation of depth of vertical cracks using surface wave testing. The performance of the hexagonal arary was evaluated on a validation bridge containing numerous artifical defects (delaminations, surface-breaking cracks, segregated aggregates, partially grouted tendon ducts, and accelerated corrosion test regions). The results from performance evaluation on delaminated and cracked sections of the validation bridge are presented.

bridge decks; delamination; cracks; impact echo; surface waves; air-coupled sensors; microphones