Abstract
It is well known that carbonation of concrete initiates corrosion of reinforcing steel by lowering the pH value, but the extent and variety of possible damage has limited research data and there exists a difference of opinion between various researchers while defining the critical carbonation depth in relation to the initiation of steel corrosion in fully carbonated concrete. Therefore, in this research experiments were conducted under severe environments for carbonation progress and measurements were obtained for carbonation depth, corrosion potential and corrosion mass loss due to carbonation under air dry condition. Also, carbonation induced electrochemical corrosion model was developed by our research group at the University of Tokyo and its authenticity was checked in the light of experiment results obtained in this research. Combined with the measurement of carbonation depth, half-cell potential values were determined so that a relation can be developed between the carbonation depth and corrosion potential. The objective is to observe the behaviour of carbonation depth-corrosion potential profile and determine the critical carbonation depth if any. It is found that the corrosion potential values vary with time domain and depth of carbonation. The carbonation induced corrosion does not start until carbonation depth reaches a certain critical level from the steel rebar. Another interesting fact that was seen from the experiment results of this research is that the half-cell potential values after the carbonation reaches the rebar level rise again. The reason is sought to lie in the varying resistivity of carbonated concrete. Compared to chloride induced corrosion in general, the carbonation induced corrosion can be pronounced as a low rate of corrosion reaction. However, it should be mentioned here that in case of carbonation induced corrosion high relative humidity plays a decisive role. The comparison of carbonation induced electrochemical corrosion model analysis and experiment results shows a fair agreement. The carbonation induced electrochemical corrosion model reasonably predicts the behaviour of corrosion for normal air dry relative humidity conditions. The electrochemical model developed also shows fair qualitative simulation for various pH levels.