69 Guided Wave Technique for Corrosion Detection in Reinforced Steel Bars Umar Amjad, Susheel Kumar Yadav and Tribikram Kundu Department of Civil Engineeing and Engineering Mechanics The University of Arizona, Tucson, AZ 85721 (520) 621-2403; e-mail umaramjad@email.arizona.edu (520) 621-2403; e-mail susheel@email.arizona.edu (520) 621-6573; e-mail tkundu@email.arizona.edu ABSTRACT Guided wave techniques are very promising for damage detection in pipe and plate like structures. Longitudinal guided waves are excited and recorded after transmission for corrosion detection in reinforcing steel bars. Apart from recording the amplitude of the transmitted guided waves or in other words, monitoring the attenuation of guided waves, differential time- of-fight is recorded with high temporal resolution using cross-correlation technique. It is found that corrosion can be detected from the TOF change as well. Feature extraction techniques are used from time-frequency representations. INTRODUCTION Oxidization of steel bars either in open environment or inside concrete causes corrosion. Any small damage (such as crack) in concrete can provide enough resource to corrode steel bars to its failure. In recent years researchers are making a lot of effort to develop a technique by utilizing guided acoustic waves to detect the corrosion of reinforcing steel bars in concrete. The feasibility of detecting interface degradation and separation of steel bars in concrete beams has been studied by Miller et al. (2013) [1] using guided Lamb waves. Lamb waves can travel a long distance and distinctly identify any change in interface bonding. The majority of research related to longitudinal guided waves focuses on examining the amplitude of the waves propagating through a material. This research however, goes in a different direction. We investigate the change in the time-of- fight (TOF) [2, 3] of the waves with respect to the variation in corrosion in steel bars. Experimental Setup Two steel bar samples are corroded for different time durations using corrosive chemicals and then the experimental data obtained from these samples are compared with that from a non-corrosive sample. All three samples are of same length. For data acquisition, guided wave set up is established in transmission mode so that refections and other shortcomings related to pulse echo method can be neglected at this time. Longitudinal guided waves are excited and studied in transmission for corro- sion detection in steel bars. A chirp signal is excited from 50 kHz to 200 kHz in transmission. Figure 1: Schematic of the experimental set up. From 2013 ASNT 22nd Research Symposium Paper Summaries, March 2013. ISBN: 978-1-57117-240-2. Copyright © 2013 by The American Society for Nondestructive Testing, Inc. No part of this document or its contents may be copied, uploaded to the internet, or stored in any shared retrieval system.