Computer Aided Modeling of Magnetic Behavior of Embedded Prestressing Strand for Corrosion Estimation

This work presents a novel computer model which simulates the main magnetic flux (MMF) signal of prestressing strand subjected to a magnetic field. Magnetic inspection techniques have been shown to be effective in detecting hidden corrosion in embedded prestressing steel strand. However, such systems are not yet ready for field application. The development of computational models is a key step in making the technology practical. Magnetic behavior of prestressing steel strand is a feature that can be used to determine loss of mass or other defects in the strand. The magnitude of the MMF induced in the strand can be used to estimate the cross-sectional area of healthy steel in the strand. Thus, magnetic properties can be utilized to measure the amount of hidden corrosion in the strands embedded in prestressed bridges and, hence, be used to determine the capacity of the bridge. An MMF electromagnet-based sensor system was recently developed for corrosion detection using the same principle. 2D and 3D models of this sensor are developed using commercially available magnetic field simulation software. The models are validated using laboratory results from tests with prestressing strands using the MMF electromagnet-sensor system. A number of factors including diameter of the strand, thickness of the concrete cover, reluctance in the magnetic circuit and variations due to temperature rise that affect the magnitude of the induced magnetic field are considered. Accuracy of the model is compared with laboratory and theoretical values. The computational model can be used to estimate corrosion from field test results and advance the development of the MMF electromagnet-sensor system.