Melanie Johnson with adviser P. L. Chapman

Corrosion damage poses a serious threat to the structural integrity of concrete infrastructure. When steel embedded in concrete corrodes, rust, which has no strength and has a large volume, gradually replaces the steel. The reduced strength of the structure diminishes further when the larger rust volume causes the surrounding concrete to crack. Once the concrete cracks, water and de-icing salt can reach the steel more quickly and exacerbate the deterioration.

Corrosion of the infrastructure causes an estimated 6 to 10 billion dollars of damage per year in the United States. There is no reliable non-destructive testing method to detect the presence of corrosion or the rate at which corrosion occurs. Existing methods, such as visual inspection and half-cell potential measurements, are unable to fully characterize damage. The goal of this project is to develop a new sensing technique
based on magnetic field measurements that will accurately measure both the state and rate of corrosion in reinforcing steel.

Working jointly with a group in the Department of Civil and Environmental Engineering, the project seeks to employ giant magneto-resistive sensors to measure the small magnetic field generated by electric currents caused by corrosion. However, to extract the magnetic field information from background noise, a model is necessary to determine the defining characteristics of the corrosion magnetic field. Three models have been developed to simulate the corrosion magnetic field. They calculate the magnetic field based on random current distributions designed to reflect the behavior of currents in general micro-cell corrosion. The models use finite element analysis and two variations on Biot-Savart law to calculate the magnetic field. Measuring the change in this simulated magnetic field shows promise in revealing corrosion magnetic field characteristics.

This project is supported through National Science Foundation Grant NSF CMS 06-25996.