Service life of undersea RC circular lined tunnel subjected to chloride attack

This investigation presents an analytical model that predicts the service life of undersea reinforced concrete (i.e., RC) circular lined tunnel exposed to chloride environment. The analytical model includes the chloride transport stage, chloride corrosion stage, and structural deterioration stage. The analytical model uses a double-layer composite medium convection-diffusion model to simulate the chloride transport stage within undersea RC circular lined tunnel that incorporates the grouting layer. The progression of chloride corrosion stage is determined based on the corrosion rate of steel bar and the volume of corrosion products. To describe the structural deterioration stage, a relationship between the volume of corrosion products and the deformation of surrounding concrete is established. The proposed transport analytical solution is then assessed against COMSOL numerical modeling and experimental data. Parametric studies are conducted to explore the influence of parameters related to the three stages on the service life of undersea RC circular lined tunnel. The results demonstrate that the service life during the chloride transport stage is inversely related to the chloride concentration and pressure in seawater, as well as the permeability of the concrete. When accounting for the time-dependent surface chloride concentration, the corrosion time of steel bar is extended by 29.4 years, reaching 49.9 years, compared to a constant surface chloride concentration scenario, which is 20.5 years. Furthermore, when considering the time- dependent concrete parameters, the corrosion time of steel bar is delayed to 48.98 years, which is 19.96 years longer than under conditions of constant concrete parameters (29.02 years). The service life of chloride corrosion stage is linearly negatively correlated with water-cement ratio, essentially unrelated to radius of steel bar, exponentially negatively correlated with corrosion product density, and linearly positively correlated with the porosity between steel bar and concrete. The duration of the chloride corrosion stage associated with the formation of Fe3O4 (47.2 days) is 19 days longer than that for the formation of Fe(OH)3 & sdot;H2O (28.2 days). The service life of structural deterioration stage is linearly negatively correlated with Poisson's ratio of concrete, exponentially negatively correlated with elastic modulus of concrete, and linearly positively correlated with tensile strength of concrete.