Role of Oxygen and Humidity in the Reinforcement Corrosion

Corrosion of reinforcement is produced when the carbonation front or the chloride threshold reaches the surface of the steel bars. The carbonation progresses when the concrete pores are not filled with water being prevented when these pores are highly water saturated. In the case of chlorides, reversely, the penetration is slower if the pores are not saturated, being negligible if the relative humidity is low. Degree of concrete saturation plays then a crucial role in the advance rate of the aggressive fronts. In addition to water, oxygen plays as well an important role in the steel depassivation stage. In carbonation case, oxygen is available as the pores are not filled with water, while in the case of the chlorides is the opposite and the amount of oxygen is that dissolved in the pore solution. In the stage of corrosion propagation, the oxygen is much less critical due to the autocatalytic nature of the corrosion, being however the humidity an essential element. These aspectswill be commented and illustratedwith results. The correct interpretation of the role of humidity and oxygen is an essential element in the assessment of existing structures.