The MFL technique – Basic application for PT cable break detection in concrete structures

From the beginning of building techniques creating pre-stressed and accordingly post-tensioned concrete structures until the late 1980ies manufacturers and construction companies dealt with pre-stressing steel material vulnerable to stress corrosion cracking. Almost every load-bearing structure requires regular inspection on a mandatory basis. Due to knowledge of pre-stressed structural reinforcement susceptible to stress corrosion cracking being used during construction or visible damage alongside the tendon area arises the demand for detailed investigation of cracks within the post-tensioned steel elements. Even though the pre-stressed steel elements of a structure are not especially at risk for stress corrosion cracking by its manufacturing process, the natural deterioration of the building fabric and manifold eventual defects and failure during structure erection encourage the requirement for an inspection of their structural integrity at least within the most important load-bearing areas. Therefore needed investigations can be carried out by application of the non-destructive magnetic flux leakage measurement technique for single bar elements and stranded wire tendons even inside cladding tubes. This testing method is subject to successful research work for more than 30 years now and has proven its validated functionality with impressive results on a big number of investigated structures including bridge elements, truss beams and container components.Starting with the basic physical measurement principle of magnetic flux leakage for dipole-formation in the area of fractures of the magnetized pre-stressed steel elements this document presents the practical application possibilities and development history of the testing method.With the consecutively presented further development of the BetoFlux-System we can provide a piece of testing equipment which combines the advantages of a pure physical measurement principle with the economical requirements for an on-site-application to investigate pre-stressed reinforcing steel elements at an early stage prior to structural collapse hazards