Effect of carbonation on release of bound chlorides in chloride-contaminated concrete

In this paper an experimental study is presented on the interaction between concrete carbonation and chloride attack. The experiments are carried out on chloride-contaminated cement pastes that have been exposed to a carbon dioxide environment. Free and total chloride contents at different carbonation times are measured in the tested specimens using traditional leaching and acid-soluble methods. Bound chloride contents are calculated from the measured total and free chlorides. The experimental data show that the carbonation of cement paste results in a release of bound chlorides, which is related to not only the decomposition of Friedel's salt, but also the decomposition of calcium-silicate-hydrate (C-S-H) gel. Based on the obtained experimental results, a numerical model is also developed for simulating the carbonation process of the chloride-contaminated cement paste. The model can be used to explain how the bound chlorides are released in a chloride-contaminated cement paste under the influence of carbonation reactions.