Diffusion-Based Model for Predicting Chloride Ingress into Road Structures

Chloride transport mechanisms into road structures are multifarious. Because the current level of knowledge is not sufficient to model all relevant transport mechanism, the approach chosen to model chloride ingress should capture the decisive mechanisms involved. Based on this idea, Fick's 2nd law of diffusion has been selected as the basic physical approach. With this approach the apparent diffusion coefficient is one of the key variables. To improve the accuracy of the approach this variable has been adapted empirically. As for concrete exposed to intermittent splash water the profile may have a maximum content inside, Fick's 2nd law of diffusion cannot be applied without restrictions. The two published approaches regarding this issue will be discussed and assessed. For the selected approach, the empirical adaptation of the apparent chloride diffusion coefficient has been carried out by evaluation of chloride profiles. The regression variables derived have been quantified stochastically to enable a full-probabilistic calculation of the predicted chloride profile. Finally, an example calculation has been carried out to demonstrate the application of this model within the framework of service life design.