Numerical Simulation Of Non-uniform Corrosion Of Steel Reinforcement Based On Concrete Micro-structure

Chloride ion erosion is the main cause of reinforcement corrosion in concrete,and reinforcement corrosion is an important disease in the durability design of concrete structures.Chloride ions from the surface of the structure into the concrete will destroy the alkaline environment of the steel bar,resulting in corrosion of the steel bar.In this paper,from the perspective of concrete meso-structure,the non-uniformity of reinforced concrete material is considered as a composite material composed of coarse aggregate,mortar and steel bar,etc.On this basis,the non-uniformity corrosion of steel bar is numerically simulated by using electrochemical corrosion theory.The research work and conclusions are as follows:1.Matlab language was used to write two-dimensional meso-concrete modeling program.Firstly,according to Fuller gradation curve and Walraven equation,coarse aggregate gradation was calculated,and then "median particle size method" and "representative particle size method" were used to generate coarse aggregate with regular polygon and random polygon shape,respectively.Then the "radius discriminant" and "maximum radius discriminant" were used to put the coarse aggregate,and finally the concrete meso-model was generated.2.The diffusion model of chloride ion in concrete is established based on Fick’s second law.The numerical results are in good agreement with the existing experimental data,which proves the reliability of the model.The effects of coarse aggregate,interfacial transition layer and crack on the diffusion of chloride ion in concrete are analyzed by using this model.The results show that the macroscopic diffusion behavior of chloride ions is mainly affected by the dilution effect of coarse aggregate.The interfacial transition layer effect and crack both accelerate the diffusion rate of chloride ion in concrete.3.Based on Fick’s second law and Butler-Volmer’s law,a two-dimensional corrosion model of reinforcement is established.The accuracy of the model is verified by comparing with the experimental data.By analyzing the numerical simulation results,it is found that the mean value of the total corrosion current density is the superposition result of the mean value of the macro cell corrosion current density and the mean value of the micro cell corrosion current density,the first half of the total corrosion current density decreases rapidly,and the second half of the total corrosion current density decreases slowly.According to the relationship between the corrosion current density of micro-cell and macro-cell,the corrosion zone can be divided into macro-cell corrosion dominated zone and micro-cell corrosion dominated zone.4.Establish a steel reinforcement corrosion model considering the concrete microstructure,and analyze the influence of coarse aggregate on the corrosion law of steel reinforcement.The results show that the corrosion process of steel bars can be divided into three stages: noncorrosion,corrosion zone expansion,and full-section corrosion.Increasing the coarse aggregate content can prolong the duration of the non-corrosion stage and the corrosion zone expansion stage of the steel bars;The side corrosion has the largest depth,and the side facing away from the eroded surface has the smallest corrosion depth.Coarse aggregates can change the diffusion path of chloride ions,resulting in irregular changes in the corroded cross-section of the steel bar,and there are tiny protrusions and depressions on the corroded cross-section.