Rapid Scanning Approaches for Ultrasonic Imaging of Concrete

Instruments and methods for ultrasonic imaging of concrete have been developed to a sufficient level. In contrast, the measurement process is too time- consuming to encourage broad application. In particular, the coupling process makes scanning of plane apertures a tedious task. This contribution discusses three coupling approaches that have the potential to permit rapid scanning. The merits of water coupling, dry coupling, and air coupling are compared, and two- and three-dimensional images are presented that make use of a newly developed mechanical scanner. From the results it can be anticipated that ultrasonic imaging of concrete can be applied in an economically efficient way. The development of ultrasonic imaging techniques for the application at concrete has reached a state that already allows solving a number of practical tasks. Imaging methods such as B-scan or SAFT (Synthetic Aperture Focusing Technique) reconstruction have been shown to enable thickness measurement, detection of tendon ducts, and flaws, and can expose the inner structure of concrete elements (1, 2). For regular use, additional progress is desirable concerning the efficiency of these techniques. Up to date especially the measurement process is time consuming. A large number of single measurements is necessary to limit the effect of structural noise and thus to enhance image quality. Due to the tedious coupling effort, every single measurement takes a relatively large amount of time. This is especially true for scanning two-dimensional apertures needed to provide a complete three-dimensional view of a concrete section. In this case, measurement times exceed SAFT reconstruction times. This contribution presents and compares approaches that make a rapid and therefore economical application of ultrasonic imaging of concrete possible. Firstly, the coupling process is considered. Here, water coupling, dry coupling, and air coupling are presented that all promise to accelerate the coupling process and allow for automated scanning. Then, a 2D/3D mechanical scanner is presented that has been developed to apply these coupling techniques in the laboratory and in the field. Two- and three-dimensional SAFT reconstructions show some of the possibilities inherent in the presented approaches.