Progress in ultrasonic imaging of concrete

Among present non-destructive methods for concrete evaluation, ultrasonic testing uses relatively short wavelengths and therefore has particular potential for detailed assessment of concrete. Methods like SAFT (Synthetic Aperture Focusing Technique) and tomographic reconstruction are able to provide high-resolution images of concrete areas, which can be employed for tasks such as area imaging, duct localization, fault detection, and thickness measurement. This contribution is intended to give insight into some of the principles and possibilities of ultrasonic concrete imaging using SAFT and tomographic reconstruction. It thereby reviews progress that has been achieved at the author's institute during the last years. For SAFT reconstruction, the processing steps are explained that are necessary to obtain an image that is easy to interpret, including the influence of transducers, their coupling, and image noise suppression. Quantitative evaluation of ultrasonic images enables the examination of tendon ducts for voids and the objective assessment of image quality. A field example demonstrates the possibilities of SAFT reconstruction. In a separate section, ultrasonic tomography is shown to have the capability to detect faults such as honeycombing in concrete pillars. Finally, the potential of ultrasonic imaging and remaining steps necessary to open broad practical application are described. (c) 2005 RILEM. All rights reserved.