United States Department of Transportation
i
Magnetic Flux-Based Nondestructive Evaluation Technologies for Assessing Corrosion Damage in External and Internal Post-Tensioned Tendons: Development Efforts and Evaluation Results
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2022-12-01
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[PDF-9.07 MB]
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Edition:Final Report
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Abstract:This report presents research work related to developing and evaluating magnetic flux-based nondestructive evaluation (NDE) technologies for detecting corrosion damage in external and internal post-tensioned (PT) tendons. For the external tendons, two types of magnetic main flux method (MMFM) systems—a solenoid type and a permanent magnet type— were developed and validated in the laboratory and in the field. The solenoid-type MMFM system was the most accurate NDE method. Its lowest damage detection limit would be 0.4-percent section loss for the point measurement method and 1.0-percent section loss for the scan measurement method. The permanent-type MMFM system is suitable for locating potential problem areas containing more than 3.0-percent section loss in external PT tendons. It has more versatile applications in the field because of its simpler hardware and speedy operation. Ideally, both MMFM systems can be employed in sequence during the field investigations: the permanent magnet type identifies potentially problematic areas by quickly scanning all suspected tendons, followed by the point measurements in the suspicious areas with the solenoid type. A return flux method prototype was developed for the internal tendons. It reached the immediate goal of detecting relatively small section losses hidden in internal tendons in laboratory environments and proved its concept successfully. It could detect a section loss larger than 15.3-percent in internal mockup tendons surrounded by vertical rebars at 6.0-inch or wider spacing when the clear concrete cover was less than 7.5 inches for metal ducts and 6.5 inches for polyethylene ducts. Without interference from the vertical rebars, as little as 9.0-percent section loss could be identified at the 6.0-inch cover. However, poor results were obtained in the anchorage zone in the box girder specimen. It is recommended that the present prototype be further improved to make it a field-deployable NDE system.
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