Abstract
Initiation of corrosion of steel in reinforced concrete (RC) structures subjected to chloride exposures mainly depends on coefficient of chloride diffusion, Dc, of concrete. Therefore, Dc is one of the key parameters needed for prediction of initiation of reinforcement corrosion. Fick’s second law of diffusion has been used for long time to derive the models for chloride diffusion in concrete. However, such models do not include the effects of various significant factors such as chloride binding by the cement, multidirectional ingress of chloride, and variation of Dc with time due to change in the microstructure of concrete during early period of cement hydration. In this paper, a review is presented on the development of chloride diffusion models by incorporating the effects of the key factors into basic Fick’s second law of diffusion. Determination of corrosion initiation time using chloride diffusion models is also explained. The information presented in this paper would be useful for accurate prediction of corrosion initiation time of RC structures subjected to chloride exposure, considering the effects of chloride binding, effect of time and space on Dc, and interaction effect of multidirectional chloride ingress.
Highlights
During the last several decades, a large number of reinforced concrete (RC) infrastructures have been built using steel and concrete
An updated overview of the following aspects of chloride diffusion process in concrete structures is presented so that the prediction of time to initiation of reinforcement corrosion would be made with more degree of accuracy: (i) The influence of chloride binding on the coefficient of chloride diffusion in plain and blended cement concrete (ii) The effect of time and space on the coefficient of chloride diffusion (iii) Models currently available for the prediction of time to initiation of reinforcement corrosion of RC structures considering the effects of chloride binding, time, and space
The diffusion-reaction model would predict a longer corrosion initiation time than the models that do not consider the effect of chloride binding during the chloride diffusion process [9]
Summary
During the last several decades, a large number of reinforced concrete (RC) infrastructures have been built using steel and concrete. The effect of chloride binding in concrete on the corrosion initiation is twofold: (i) the rate of ionic diffusion of chloride in concrete is reduced, since the amount of available mobile ions (free chloride) is reduced due to binding mechanisms and (ii) the reduction of free chlorides in concrete results in lower amounts of chlorides being accumulated at the reinforcing steel layer [13]. (i) The influence of chloride binding on the coefficient of chloride diffusion in plain and blended cement concrete (ii) The effect of time and space on the coefficient of chloride diffusion (iii) Models currently available for the prediction of time to initiation of reinforcement corrosion of RC structures considering the effects of chloride binding, time, and space. The diffusion-reaction model would predict a longer corrosion initiation time than the models that do not consider the effect of chloride binding during the chloride diffusion process [9]. It is reported that no single binding isotherm can accurately express the relationship between free and bound chloride within the complete concentration range [14]
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