Prediction of Chloride Penetration into Saturated Concrete Multi-Species Approach

Doktorsavhandling, 2000

The cost due to rehabilitation of corroded reinforced concrete structures is a worldwide matter of concern. The mechanisms of reaction-diffusion involved during the transport of chloride ions into saturated concrete, which are initiating the corrosion process, are therefore studied in this thesis. The literature review shows that numerous experimental test methods and models exist today leading on to comprehension and description of chloride ion transport. However, the different parameters obtained empirically are often difficult to compare and some experimental observations remain yet unexplained. Starting from this state of the art, a quite new theory in the civil engineering research domain, called the multi-species approach, is presented. This approach, which makes it possible to account for the interactions between the different species present in the electrolyte solution, has been used to simulate multi-species diffusion and migration in saturated reactive porous media. New numerical software, called MsDiff, for Multi-species Diffusion, has been developed in order to describe many situations involving chloride ion transport. From MsDiff, several experimental results found in literature, the significance of which had not been fully understood, could finally be explained. Then, MsDiff was used to simulate immersion test procedures for various concrete mixtures. The simulations, conducted as a sensitivity study, showed which phenomena had the most significant influence on chloride ion diffusion. Among them, the chloride binding phenomena and the pore solution composition seem to be the most decisive one. Finally, the simulations clearly demonstrated that it is not reasonable to use an empirically based method to predict chloride penetration. The use of Fick's law of diffusion for making long-term predictions is therefore strongly challenged.