Chloride Transport Parameters of Carbonated Concrete

Many concrete structures suffer from corrosion of reinforcing steel due to chloride penetration and carbonation, and it is common for both deteriorations to progress simultaneously. Carbonation of concrete significantly changes the properties of concrete, so that cement hydrates is decomposed and the microstructure is also changed. The chloride penetration of carbonated concrete is bound to be significantly different compared to non-carbonated concrete. For this reason, chloride penetration parameters of carbonated cementitious materials were examined in this paper, i.e., (a) surface chloride content, (b) chloride diffusivity, (c) chloride adsorption capacity, and (d) critical chloride content. Each material parameter was calculated from the material parameter model reflecting the change in porosity due to carbonation. Carbonation of concrete converts cement hydrates into Calcite, resulting in almost loss of chloride adsorption capacity. Even though the pH is slightly decreased due to carbonation, critical chloride content of carbonated cementitious materials was calculated, confirming that the reinforcement is very vulnerable to corrosion. Since the main parameters are affected by mixing properties of cementitious materials, the analysis was performed for concrete mixes with arbitrary assumed conditions. Since the parameters change at each cement hydration stage, their time evolution was expressed. This study is expected to be useful to develop a chloride penetration model of carbonated cementitious materials in the future.