The Remanent Magnetism Method (RM-method) is a non-destructive method to identify potentially unsafe conditions in pre-tensioned and post-tensioned concrete structures. The RM-method identifiesfractures in single pre-stressing wires, even when they are bundled with intact wires. Fractures produce characteristic magnetic leakage fields, which are measured with Hall-Effect sensors. The magnetic field of the tendons is measured at the concrete surface, once they have been pre-magnetized with an electromagnet.The parameters associated with fractured wires are the intensity of the magnetic poles, the distance between tendon and concrete surface and the crack width.The knowledge of these parameters allows drawing conclusions about the reduction of the cross-sectional area or the number of fractured wires in a tendon.The method has been evaluated by the German Federal Highway Research Institute (BundesanstaltfürStra?enwesen, BASt) and is going to be described in a DGZfP directive (German Association for non-Destructive Testing).The test results are indicated just in time in a gray-scaled magnetic laptop picture.
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