Visual images that describe the location, size and shape of embedded defects provide direct information about the condition of a structure. Many individual data are needed to construct an effective image however, and the inherent large size of concrete structures results in an enormous amount of data needed to construct an adequate image. One approach to empower the application of ultrasound for such imaging is to eliminate the need for physical contact between the sensor and tested structure. The PI has recently completed research on air-coupled ultrasonic testing for concrete. The research findings illustrate that ultrasonic waves traveling through concrete can be detected with a fully contact-free configuration using air-coupled sensors. In this project, the efficacy of air-coupled ultrasonic tomographic imaging will be investigated. The methods will first be evaluated experimentally using reduced-scale (fifth-scale) concrete column samples. Both rectangular and circular cross-sectioned column samples will be considered for each scan configuration. Some concrete samples will contain embedded artificial volumetric (void) and planar (crack) defects. Other defect-free specimens will be subjected to simulated seismic loads, using the fifth-scale test facility at the University of Illinois. Application to full-scale concrete columns, which are currently being tested as part of a NEES small group project at the University of Illinois, will then follow; the columns will be non-destructively imaged before and after the mechanical (seismic) loading is applied as part of the NEES project. Successful completion of the work will enable unparalleled internal defect characterization for concrete structures. At the same time, the effort provides a unique opportunity to extend development of an emerging technology that is currently being developed by the PI: air-coupled sensing for concrete structures.
