Corrosion of reinforcing steel in concrete structures is the most serious durability issue for civil engineering infrastructures. To effectively control corrosion, accurate detection of the corrosion degree is necessary. In this thesis, two new types of apparatuses for corrosion condition detection of reinforced steel have been developed based on the magnetic field change of the rebar due to the rust development on the surface

It is well known that there is an extreme difference of magnetic permeability between corrosion product and reinforced steel. For corrosion product, ferric iron dominates the magnetic response with similar permeability of concrete while for reinforcing steel the value is two magnitude higher. The developed apparatus induces an electromagnetic field on the...[ Read more ]

Corrosion of reinforcing steel in concrete structures is the most serious durability issue for civil engineering infrastructures. To effectively control corrosion, accurate detection of the corrosion degree is necessary. In this thesis, two new types of apparatuses for corrosion condition detection of reinforced steel have been developed based on the magnetic field change of the rebar due to the rust development on the surface

It is well known that there is an extreme difference of magnetic permeability between corrosion product and reinforced steel. For corrosion product, ferric iron dominates the magnetic response with similar permeability of concrete while for reinforcing steel the value is two magnitude higher. The developed apparatus induces an electromagnetic field on the specimen through direct current accessing to the coil and collects data of specimens using Hall Effect sensor panel. Experiments have been carried out on measuring magnetic flux changes with the variation of corrosion condition of specimens. The experimental results from the different shape of specimens reveal the variational trends of the magnetic field that the absolute value of electromagnetic induction will increase as the corrosion condition get severer. To investigate the fundamental relationship between mass loss and magnetic induction changes in reinforcing concrete beam experiment, a new design Magnetic corrosion monitoring apparatus has been developed, which can be embedded inside a reinforcing concrete structure to monitor the magnetic field change around reinforced steel due to the growing of the corrosion product. Preliminary experiment result shows that the relationship between mass loss of specimens and magnetic induction changes is linear in the early stage of corrosion. To study on mass loss of reinforced steel with different specification, calibration is needed before experiments being conducted. Also, a corrosion evaluation of reinforcing steel in concrete beam by magnetic method has to verify by other methods. For this purpose, in additional magnetic corrosion monitoring device, acoustic emission detection technique and Half-cell potential measurement are utilized simultaneously in the experiment to monitor the corrosion process of rebar. It is shown that there is a good agreement in results from the three techniques. Especially, the magnetic corrosion monitoring device provides a stable and consistent results in quantitative analysis of corrosion condition level.

The major contributions of the study are:

1. An innovative electromagnetic corrosion detection device has been invented. The fabricated prototype has demonstrated that it can detect the electromagnetic field changes for specimens under different corrosion condition accurately. The apparatus has a great potential to be applied for cable corrosion detection for both suspension and cable-stayed bridges.

2. By using the newly developed electromagnetic testing device, the phenomenon of magnetic induction on reinforced steel due to corrosion condition has been observed and investigated. A new nondestructive testing method for corrosion detection by measuring the magnetic field changes has been established.

3. Based on the principle of magnetic field change theory, a brand new magnetic corrosion monitoring transducer has been invented. It can be embedded into the concrete structure for real time and on site, corrosion is monitoring for reinforcing steel. It provides an innovative continuous healthy monitoring method to ensure the safe operation of important civil infrastructures.

4. The fundamental relationship between corrosion condition level and the output signal of magnetic corrosion monitoring transducer has been investigated with reinforced concrete beam. The results have been verified with acoustic emission method and Half-cell method with satisfactory agreement.