Essay On Concrete Corrosion

3.Concrete corrosion and the stages:

3.1 Reinforcement corrosion

Reinforcement corrosion refers to the electro-chemical or chemical reaction between the reinforcement bar and the environment, causing its deterioration. The causes of corrosion in concrete can be explained practically or in terms of electrochemistry. Some of the factors affecting corrosion include the presence of aggressive species, for instance chlorides and their quantity. This species breaks down the reinforcing bar protective film thus causing corrosion. Corrosion of reinforced bars is the main cause of concrete degradation but not due to the limitations caused by the concrete itself. In effect, all Portland cement concretes provide corrosion protection of even the reinforcement bar of the lowest quality. Reinforcement steel, for example, is not stable thermodynamically in the air. This will make it to regress to the state of lower energy such as a hydroxide by reacting with water and oxygen. Surface atoms are the only ones affected since they are exposed to air. For a steel which is embedded in concrete, there is limited access of oxygen and water because of the concrete protective coating. In addition, the solution in the cement paste pores is highly alkaline, thus the corrosion products formed are insoluble. This forms a thin

Reinforced bars are normally used in severe environments like in sea water where a lot of chlorides are present. When chlorides ions enter the reinforcement bar, it destabilizes the inactive layer protecting the reinforcement bar thus causing formation of rust. Conversely, when the concrete is carbonated, the usually alkaline environment which is responsible for reinforcement bar protection is neutralized. This will make the reinforced bar stop being passive, leading to rapid corrosion. The corrosion rate induced by chloride ions is higher compared to the one induced by carbonated