Sensitivity analysis of a physicochemical model of chloride ingress into real concrete structures subjected to long-term exposure to tidal cycles

Abstract

In marine environments, reinforced concrete structures are exposed to tidal conditions and therefore susceptible to chloride ingress. Reliable models of transport are crucial in order to evaluate the service life of these structures. Unlike engineering models based on Fick's 2nd law and empirical coefficients, this study proposes a model based on a physicochemical description of the transport phenomena and on some assumptions restricting the number of inputs to 9 parameters and the computational costs. This model is validated for a long exposure to tidal cycles (28 years). Then, the sensitivity analysis, based on the Morris method, is performed through 100 simulations of tidal exposure considering different sets of the 9 input parameters. According to the critical times of initiation of corrosion predicted, the most sensitive parameters are the critical chloride concentration and the chloride diffusivity factors. The effects of moisture sorption and chloride binding parameters are moderate after long exposure. Then, the results of the simulations are compared to data of the literature in terms of convection depths and total chloride concentrations at the limit of the convection / diffusion zones. Finally, by quantitative considerations, the analysis goes further, providing analytical relations expressing the convection depth and the associated total chloride concentration as functions of input parameters. These provide physically informed guidelines in using an engineering model based on Fick's 2nd law in order to estimate the critical time of initiation of corrosion.