Magnetic Perturbation Imaging for Prestressed Concrete Evaluationby Al Ghorbanpoor,
Abstract: Many prestressed concrete bridge structures in the United States and other parts of the world are over thirty years old and have shown various signs of distress. Corrosion or fracture of prestressing steel in prestressed concrete members is considered a critical problem that could lead to possible failure of those members. To assess the condition of prestressing steel in concrete bridge members, a non-destructive evaluation (NDE) technique based on the concept of magnetic flux leakage (MFL) has been developed. Relevant instrumentation based on the MFL concept has been constructed through completing a recent study at the University of Wisconsin–Milwaukee. The equipment includes a set of permanent magnets, a set of Hall-Effect sensors, a mechanical frame that supports various necessary components, DC motors and mechanical control devices to enable the required motion and negotiation for the support frame, a computer and wireless communication devices. Figure 1 shows a photograph of the MFL equipment that is installed on a prestressed I-girder in a bridge. Two workers can install the equipment on a concrete beam during a period of only a few minutes. Through a wireless computer control, the equipment is able to scan the lower flange of a prestressed girder along its length and to construct an image of the magnetic field perturbation associated with the loss of cross sectional area of prestressing steel in the girder. Location and extent of corrosion or fracture in the prestressing steel within the concrete test girder can be obtained from interpreting the MFL data.
Subject Headings: Prestressing | Magnetic fields | Prestressed concrete | Concrete bridges | Imaging techniques | Girders | Equipment and machinery | Steel | Corrosion | North America | United States
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