Numerical Simulation Researches Of Multiphysics Coupling Chloride Ion Transport Model In Concretes

At present, Concrete structure’s duration is the hottest topic. It’s not only linked with concrete structure’s maintenance cost and service life, but also connected with social sustainable development. The key point of leading steel-bar corrosion makes chlorine salt erosion paid vitally attention. It’s important for us to establish a chloride ion transport model to predict the corrosion that bases on the researches of chloride ion transport mechanism inside the concrete. A great number of chloride ion transport model’s solution base on a single environmental effect by mean of Fick’s second law. In reality, A handful of concrete structures are in a single phase environment, the majorities are in a multiple factors coupling environment, such as atmospheric water erosion, temperature, carbonation, chlorine salt corrosion, freeze thawing in particular frozen area, etc. Therefore, we need to build a multiphysics coupling chloride ion transport model to simulate the complex environment. The thesis goes from the easy to the difficulty, firstly I improve the chloride ion transport model by multiple factors correction, then put forward a multiphysics coupling chloride ion transport model that combines with water transport and carbonation. The main contents are as follow:(1) As we know, various factors in the complex environment will do great effect to the concrete structures. Based on the Fick’s second law and considered various factors effect as part of chloride ion diffusion coefficient’s correction term, I establish an empirical model of chloride ion diffusion coefficient. Sensitivity analysis of model parameters and the researches of Cs(t) model and Cb(Cf) model then are shown;(2) Based on the water and chloride ion transport mechanism in the splash zone or tidal zone of the coastal environment, I establish the water-chloride ion convection diffusion model in the wetting-drying cycles environment. There I treat concrete’s pore solution saturation ‘s’ as an independent variable. The key coupling variable is convection velocity ‘u’. Here we use the water transport model to control the pore solution’s diffusion, using the chloride ion transport model to control the chloride ion’s convection and diffusion. Then chloride ion’s convection and diffusion in the concrete during the wetting-drying cycles environment can be simulated by the couple. Lastly, sensitivity analysis of model parameters are shown;(3) The concrete structures in complex environment suffer from water transport 、carbonation and chloride ion corrosion. Firstly, I establish the theoretical carbonation model based on carburizing reagent theory of Papadakis’ s; Then combined the water diffusion and carbonation to form carbonation-water coupling transport model; Finally combined water diffusion, carbonation and chloride ion transport to form carbonationwater-chloride ion coupling transport model;(4) Summarize the creative points of the thesis and explore deeply into the advantages and disadvantages of the coupling model, Then proposing the improvement that the coupling model ought be taken and point out the further development direction of the coupling model.