Two acoustic methods, impact echo (IE) and ultrasonic surface waves (USW), enable inspection below the surface of the concrete structure and are sensitive to the presence of damage and flaws. However, the use of conventional contact sensors to create condition maps of bridge decks is severely limited by the required physical contact and coupling of the transducers. Scan areas can consist of a very large number of measurement points. As a result, the inspection with the conventional IE and USW methods is time consuming and rather costly. The most time-consuming part of measurements with conventional contact sensors is the process of pressing the sensors against the surface at each measurement position, lifting up the sensor, moving it to the next measurement position, and ensuring good coupling. Furthermore, the application of contact sensors requires rather smooth surfaces to achieve sufficient coupling.
An effective and promising solution to this problem is to eliminate the need for physical contact between the sensor and tested structure, and the use of contactless air-coupled acoustic sensors. However, in practical applications noise from the environment, acoustic noise caused by motors or wheels when using systems in motion, and impact noise from the steel sphere itself often make the use of air-coupled sensors very difficult.
The ultimate goal of this study is to utilize a non-contact acoustic array for accurate and quick imaging of flaws inside concrete bridge decks. This study has the following five main objectives: (1) improvement of hardware including the acoustic array and air-coupled sources (ultrasonic transducer) to have a fully air-coupled testing system, (2) identification of continuous data acquisition scenarios in terms of speed and data resolution for bridge deck inspection, (3) improvement of effective signal processing schemes to eliminate noise components and to identify useful contents for both IE and USW, (4) development of an effective real-time data presentation system with 3D imaging capability; and (5) validation of the accuracy and reliability of the developed air-coupled acoustic array through laboratory specimens and actual field tests.
Nondestructive evaluation; Bridge deck; Acoustic; Robotic; Air-coupled; Automation; Surface wave; Impact echo;