In reinforced concrete structures, steel corrosion is a major factor affecting the durability and service life of the buildings. When carbon dioxide and chloride penetrate into the concrete to break down the protective oxide layer on the steel surface, corrosion will be greatly accelerated under the presence of sufficient moisture and oxygen. The expansion of rust in concrete induces pressure on the surrounding concrete. The expansion stress eventually causes cracking of the concrete cover which is very harmful to the durability and safety of structures.

Most existing studies have focused on uniform corrosion around the circumference of the steel bars in the concrete structure. However, in recent years, experimental and theoretical studies have shown that non-uniform formation...[ Read more ]

In reinforced concrete structures, steel corrosion is a major factor affecting the durability and service life of the buildings. When carbon dioxide and chloride penetrate into the concrete to break down the protective oxide layer on the steel surface, corrosion will be greatly accelerated under the presence of sufficient moisture and oxygen. The expansion of rust in concrete induces pressure on the surrounding concrete. The expansion stress eventually causes cracking of the concrete cover which is very harmful to the durability and safety of structures.

Most existing studies have focused on uniform corrosion around the circumference of the steel bars in the concrete structure. However, in recent years, experimental and theoretical studies have shown that non-uniform formation of rust, and hence the generation of non-uniform pressure around the bar, will lead to the concentration of the corrosion induced stress in the upper part of steel. With more corrosion product concentrating in the upper part of the steel, the induced stress increases more rapidly under non-uniform corrosion, and this aspect should be properly considered in the analysis of concrete cover cracking.

In this thesis, a comprehensive study on non-uniform and uniform corrosion was conducted by impressed current method. The mass loss of the steel rebar under impressed current was calculated by the Faraday’s Law and calibrated by the gravimetric method. Fibre Bragg gratings (FBG) sensors were used to monitor corrosion induced strain during the corrosion progress. Moreover, the commercially finite element software ATENA has been utilised to perform numerical analysis on cover cracking due to steel corrosion.

The results of the calibration tests indicate that Faraday's Law does not always give accurate estimation of the mass loss. The accuracy depends on the chloride concentration in the system. For both non-uniform corrosion test and uniform test, the strain vs steel mass loss shows a general increasing trend with three different stages during the corrosion progress. The curve for non-uniform corrosion is always above the one for uniform corrosion, indicating that with the same mass loss of the steel rebar, non-uniform corrosion always contributes to higher strain in the concrete.

A novel approach to accelerate non-uniform steel corrosion based on the use of an embedded cathode has also been developed. The basic concept of the novel approach is that a non-uniform electric field may induce non-uniform corrosion. In addition to experimental investigation, the finite element software ANSYS Maxwell has been used to analyse electric filed distribution, and the rust distribution around the steel reinforcement is found to be correlated with the electric field.