Degradation of concrete structures, which constitute a significant majority of the built infrastructure, due to increased demand, environmental exposure, natural and man-made calamities may lead to catastrophic failure, causing loss of human lives and to the economy. To achieve sustainability and resilience and to obtain quality service and optimal benefit from investment, research needs to be carried out on development of accurate and fast non-destructive testing techniques for assessment of concrete structures.
The first part of my talk deals with the application of ultrasonic imaging as a tool for non-destructive evaluation of concrete media. In contrast to traditional approaches, where ultrasonic pulse velocity measurements are used to assess the quality of concrete, our work applies two advanced techniques, the Synthetic Aperture Focusing Technique (SAFT), typically used in remote sensing and medical ultrasound and the Reverse Time Migration (RTM) algorithm prevalent in geophysical exploration, for detection of small debonds around rebars in laboratory scale concrete samples. The debonding is a serious issue with regard to safety and originates due to bad workmanship, slip of the rebars during casting, honeycombing etc. Our computational work and experimental investigations reveal that ultrasonic images have very consistent features that can distinguish between intact and debonded rebars.
In the second part of my talk, I demonstrate that a combination of ultrasonic and thermographic imaging can be a powerful tool for detection of rebar corrosion. An accelerated corrosion setup is developed on which both ultrasonic and thermographic imaging are performed. By applying a Fourier Transform based thermographic imaging technique, we are able to detect fine surface-breaking cracks in concrete that may otherwise be ignored. The study shows that thermal imaging being a non-contact technique has potential of assessment of large areas of the concrete structure to detect the troubled spots, which can further be assessed in detail with ultrasonic imaging. The ultrasonic imaging methodology shows that with progress of corrosion, the rebars disappear from the images, which can also be a useful diagnostic indicator for progressing corrosion.
Dr. Abhijit Ganguli is currently an Associate Professor of Civil Engineering (specialization - Structures) at the Indian Institute of Technology Tirupati, INDIA. Previously he was an assistant professor of Civil Engineering at the Indian Institute of Technology Delhi, INDIA. Abhijit obtained his Ph.D from Université Libre de Bruxelles, Belgium and had postdoctoral experience in the University of Massachusetts Amherst, at Schlumberger-Doll Research Center in Boston and in the Center for Subsurface Sensing and Imaging Systems at Northeastern University Boston, USA.
Abhijit’s primary research interests lie in the field non-destructive evaluation (NDE) and health monitoring of civil engineering structures. Specifically, he has been active in the area of phased array ultrasonic imaging as a tool for NDE of concrete structures for more than a decade. His work involves experimental acoustics, wave propagation and signal and image processing for detection of durability issues in concrete. Abhijit’s future interests lie in the development of non-contact assessment tools for efficient inspection of large scale civil structures.