Application of contactless ultrasound toward automated inspection of concrete structures

• Contactless transducers can send and receive ultrasonic surface waves in concrete.
• Distinct sensor technologies are used to send and receive signals, respectively.
• An optimal test configuration is defined and incorporated into an automated system.
• The configuration provides consistent signals regardless of surface roughness.
• The technique enables damage detection and characterization for concrete.

In this paper we demonstrate the potential of contactless ultrasonic sensing for rapid and automated characterization of concrete structures. Practical generation and detection of ultrasonic surface waves are made possible using air-coupled sensors, offering the potential to overcome limitations associated with infrastructure assessment measurements. The objective is to demonstrate enhanced performance when miniature, micro-machined sensors (MEMS) and high voltage solid-state capacitance transmitters are used in a scanning configuration, suitable for automation. The employed sensors, system and testing configuration, with respect to sensor height and incident angle, are described. An optimal test configuration is defined and incorporated into a controlled scanning system. Tests with the optimized configuration were carried out on reinforced concrete elements: a pre-stressed concrete rail tie that contains rail seat damage and concrete blocks with varying levels of simulated micro-cracking damage. In both cases, obtained surface wave velocity and attenuation signal characteristics show sensitivity to concrete material damage.