Location of Prestressing Steel Fractures in Concrete

The remanent magnetism method allows the identification of potentially unsafe conditions in pretensioned and posttensioned concrete structures by locating fractures in the prestressing steel. This nondestructive method identifies fractures of single wires, even when they are bundled with intact wires. The magnetic field of tendons is measured at the concrete surface, once they have been premagnetized with an electromagnet. Fractures produce characteristic magnetic leakage fields, which can be measured with appropriate sensors at the concrete surface. The parameters associated with fractured wires have been quantitatively identified in the laboratory and have been confirmed in the field. The knowledge of these parameters allows us to draw conclusions about the reduction of a cross-sectional area or the number of fractured wires in a tendon. The method has been successfully applied outside of the laboratory on full size bonded and unbonded posttensioned structures.