Thermodynamic difficulties to determine a critical chloride threshold for breakdown of the protective layer of steel reinforcement in a maritime concrete structure. Issue 5 (3rd September 2022) - Soive, Anthony
Abstract : There is much debate on the expression used for the critical chloride threshold as well as on its value for breakdown of the protective layer of steel for reinforced concrete. In fact, this concept suggests that the breakdown is only driven by dissolution of the protective layer. A reactive transport model including dissolution and precipitation of solid species with their kinetics is then used in order to simulate the ingress deleterious substances in a concrete exposed to seawater and the chemical degradation of the oxides and hydroxides present in the protective layers covering a steel rebar. The numerical results confirm that most of the oxides are thermodynamically very stable even after a long period of exposure, especially in the inner layer. This finding suggests that corrosion initiation depends on protective layer thickness and history. These results also provide a sound explanation why a wide scatter of values of critical chloride threshold values is reported in literature.