Corrosion of steel reinforcement is one of the main causes of damage in concrete structures. Often the corrosion of reinforcement steel is influenced by cracks in the concrete. Cracks in concrete structures are often produced due to loads, shrinkage or thermal gradients. Once a crack is formed, it disrupts the spatial continuity of concrete and leads to the corrosion of steel by the macro-cell mechanism. The steel at the crack undergoes localized corrosion, while the steel away from the crack remains passive. This paper presents the results of an experimental program which aims to investigate the response of steel, embedded inside cracked concrete and with an established macrocell, to external polarization. The results of linear polarization, performed on cracked concrete specimens containing a segmental steel bar with external electrical connections, are presented. A simple circuit-based model, which allows for predicting the polarization response of the macro-cell is presented. The results of the model indicate that there a spatial variation in the applied current relative to the crack. It is shown that the applied current primarily flows through the active steel located near the crack.
Reinforced concrete is the most widely used construction material, especially in transportation infrastructure. Many of these concrete structures, especially highway bridges, exhibit early deterioration caused by corrosion. Corrosion damage in reinforced concrete is the leading factor contributing to the deterioration of the nation?s highway infrastructure. In 1997, it was estimated that the cost of corrosion damage in US highway bridges exceeded $150 billion. The annual expenditure for repair and rehabilitation of concrete structures in the 90s has exceeded fifty percent of the total construction costs and it is expected that this trend will continue in the future. Detection and characterization of corrosion of steel in concrete, therefore, is very important for the condition assessment and initiation of timely repairs in reinforced concrete structures.
Previous research on corrosion of steel reinforcement in concrete has primarily focused on corrosion in pristine (uncracked) concrete. The factors influencing corrosion and the methods for determining the rate of corrosion of steel embedded in concrete have been extensively researched. Several electrochemical methods which provide for assessing the rate of corrosion, which is considered uniform along the entire length of the steel bar have also been developed. In these studies, it is implicitly assumed that cracking in concrete is the result of expansion stresses due to corrosion product.
The alkalinity of concrete provides good chemical protection to steel against corrosion. Therefore, in the absence of a crack, the steel reinforcement in reinforced concrete structures usually exhibits a prolonged corrosion initiation period. However, cracks are often found in concrete structures. These cracks are introduced due to the action of loads, restrained shrinkage or thermal gradients. The main transport mechanism for chloride ingress in cracked concrete is convection due to capillary suction of deicing water, which is faster than the diffusion based-mechanism in uncracked concrete. Once a crack is formed in reinforced concrete, it provides an easy and fast access for ingress of ions such as chlorides, oxygen and water to the steel surface. The steel in the crack zone is exposed to the environment and is de-passivated, which results in a faster initiation of corrosion.
Relatively little work has been done to study the corrosion of steel embedded in cracked concrete. A crack has been shown to produce spatial variations i