MAGNETIC-BASED NDE OF PRESTRESSED AND POST-TENSIONED CONCRETE MEMBERS -- THE MFL SYSTEM

This report describes all aspects of a study to develop a nondestructive evaluation (NDE) system based on the concept of magnetic flux leakage (MFL) to detect corrosion and fracture of prestressing steel in pretensioned and post-tensioned concrete bridge members. The basic methodology is based on introducing a direct-current magnetic field in close proximity of the prestressing or post-tensioning steel and monitoring the variations of the field due to loss of cross-sectional area of steel from corrosion or fracture. The mechanical and electrical components of the MFL system are described, as well as the software developed to acquire and analyze the MFL data and to control all hardware. The system is designed and fabricated to offer ease of use during the field operation. Although most of the effort made during this study was associated with the development of the MFL system, limited laboratory and field investigations were conducted to assess the capabilities and limitations of the system. Additional laboratory and field investigations are recommended.