"Nondestructive testing of civil infrastructure using mechanical waves"
by: Giovanni Cascante, University of Waterloo
Nondestructive testing (NDT) is a critical step for the success of maintenance and safety programmes currently developed by construction and government agencies. Condition assessment is typically based on in situ measurements of material strength. These measurements are commonly performed using intrusive tests; however, these tests are expensive and in many cases impossible to perform. Conversely, nondestructive tests (NDT) such as ground penetrating radar (GPR) and ultrasonic surveys are non-intrusive, fast, and economical; they can reveal structural damage - such as fracturing, debonding, and corrosion - that cannot otherwise be detected. GPR and seismic equipment has been successfully used for the condition assessment of civil infrastructure. However, the problem is complex and both methods can produce false positives. Therefore, new reliable techniques to perform cost-effective maintenance and rehabilitation programmes are needed by infrastructure managers.
This presentation covers the basics of wave propagation methods, the importance of transducer characterization, and the use of numerical simulations to explain wave-material interaction. Typical experimental results from nondestructive tests on concrete plates, asphalt pavements, and an earth embankment will be discussed. Experimental results show that the main components of ultrasonic equipment introduce a characteristic time delay in the response of the system; which is responsible for significant errors in wave-velocity measurements. Based on numerical and laboratory results of ultrasonic tests, the actual responses of ultrasonic transducers are measured and evaluated. The 2D-Fourier and wavelet transforms are used in the analysis of surface responses to extract information of the fundamental Lamb mode in concrete and asphalt plates. A proposed wavelet transmission coefficient (WTC) is shown to be sensitive to the crack and joint depths. Finally, experimental and numerical results show that surface wave tests can be successfully used to determine the surface location of buried trestles in an earth embankment.
Dr. Giovanni Cascante serves as an Associate Professor at the University of Waterloo; he holds a B.Sc. degree in Structural Engineering (University of Costa Rica), a M.Sc. in Earthquake Engineering (Central University of Venezuela), and a Ph.D. in Geotechnical Engineering (University of Waterloo). Before joining the University, he worked as a Project Engineer (Trow Consulting Engineers Ltd.), Research Assistant and Post-doctoral Fellow (University of Waterloo), and Research and Consulting Engineer (Intevep S.A. and Coral 83 S.R.L). His areas of expertise are in nondestructive testing of civil infrastructure using mechanical waves, dynamic soil characterization (resonant column, BE, and ultrasonics), signal processing, numerical simulations of wave propagation, and vibration measurements. The main objective of his current work is to improve and develop nondestructive testing techniques for civil infrastructure based on a fundamental understanding of wave propagation in geo-materials. Dr. Cascante has authored more than 50 technical publications, including award-winning papers (ASTM 2005, SAGEEP 2005, TAC 2006). Dr. Cascante is associate editor for the GTJ-ASTM and the JEEG journals and is a member of several professional societies.