Post-Tensioned Tendon Inspection and Structural Health Monitoring

A recent discovery of chloride contaminated grout in P-T tendons has lead to a heighten awareness of pending tendon failure. Tendons have failed on several U.S. bridges and in Europe, some only 7 and 15 years old. In the UK corroding internal tendons have closed a major bridge in London. In Virginia and Texas tendons have broken. Inservice P-T tendons inspection methods are still not well known to DOTs. Tendons were designed to be maintenance free, but by this same virtue they are also difficult to inspect since the steel tendon is inaccessible because of grout and being encased in metal or plastic and sometimes buried in concrete. Common problems associated with tendon failures are corrosion from chlorides or other contaminates, voids and wire breaks. Coring the tendon for grout samples violates the integrity of what may have been a good tendon and then makes it susceptible to future failure. Our NDT and SHM (structural health monitoring) experience in research and field inspection presented us with access to more than >3,000 NDE experts. After surveying these experts around the world our scientists and engineers found several ideal technologies and some with field experience for these applications. Methods that were discussed as possible solutions for P-T tendon inspection were ultrasonics, phased array ultrasonics, radiography, computed digital radiography, ground penetrating radar, magnetic particle, magnetic flux leakage, eddy current, electromagnetics, vibration and strain gages, impact echo, acoustic emission and infrared thermography. Magnetic flux leakage has shown promise for metals loss and have been published by University of Wisconsin. We investigated five other methods/technologies. This paper discusses five noninvasive technologies for P-T tendon inspection and monitoring.

References
1. Phil Cole and Jon Watson. “Acoustic Emission for Corrosion Detection”, 3rd MENDT - Middle East Nondestructive Testing Conference & Exhibition - 27-30 Nov 2005 Bahrain, Manama. 2. Washer, Ph.D, P.E., Glenn M. ASCE - Highway Bridge Inspection, Testimony of The American Society of Civil Engineers Before the House Committee on Transportation and Infrastructure on Highway Bridge Inspections October 23, 2007 Chairman DeFazio, Congressman Duncan and Members of the Committee. 3. Van de Loo, P.J. and B. Herrmann. How Reliable is Acoustic Emission (AE) Tank Testing? The Quantified Results of an AE User group Correlation Study. 4. Yuyama, S. Acoustic Emission Evaluation of Corrosion Damages in Buried Pipes of Refinery Petroleum Refining Engineering Center Japan Energy Corporation, Nippon Physical Acoustics Ltd. Japan T. NISHIDA. 5. Pollack, Adrain. Acoustic Emission Capabilities and Applications in Monitoring Corrosion, ASTM Publication, 1986.
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