In durability diagnosis of RC structures and design, particularly for structures at sea shores, it is necessary to consider the relation between the amount of air laden chlorides and penetrating chloride ions in concrete.
This paper proposes a model representing the relation mentioned above. This relation has not been solved clearly since this involves many difficult problems. The proposed model can take account of washing out and penetration of chloride ions from concrete surface. These characteristics are represented by the flux of chloride ions and the flux is used as the boundary condition for solving the diffusion equation.
In analysing the diffusion equation of chloride ion-penetration in concrete, this proposed model takes account of characteristics such as reduction of chloride ion-penetration in concrete with time and redistribution of chloride ions due to carbonation of concrete.
To start with the analysis, the rate of penetrating and washing out of chloride ions at the concrete surface and the characteristics of chloride diffusion in concrete are unknown. Therefore, these characteristics are determined by the test results obtained from two RC test structures exposed to the sea for 7 and 12 years, respectively. These RC test structures were constructed along seashores in the northern part of the Okinawa Island.
By using the proposed boundary conditions and the diffusion model, numerical analysis has been performed and the results are compared with the data obtained from various field tests.
Evaluating the results, the following conclusions are obtained.
1) When the amount of air-laden chlorides exceeds a certain level in relation to the amount of penetrating chloride ions in concrete, the penetrating rate of chloride ions does not increase. This phenomenon is represented by the idea originated from Langmuir absorption theory.
2) The difference in the amount of penetrating chloride ions due to environmental conditions has been clarified, where the conditions exposed to rain or not are considered.
3) The barrier effect of chloride penetration due to the finishing of the concrete surface has been presented in this analysis.
4) The proposed method is able to deal with actual phenomenon and represent the characteristics resulting from various water-cement ratios and different amounts of air-laden chlorides. It is concluded that the proposed method gives excellent results.