Multi-scale Numerical Simulation Approach For Coupling Effect Of Concrete Cracking And Chloride Ion Diffusion In Reinforced Concrete

In order to meet the growing demand of Chinese transportation industry,a large number of roads and railway bridges with reinforced concrete as raw materials have been put into use.The service environment of the bridges is not the same due to a vast territory of China.With the expansion of the application of concrete bridges,more and more concrete bridges are used in harsh environments.At present,the disease and collapse accidents of bridges are not uncommon.Many bridges in China are faced with the problem of how to ensure the safety and durability of bridges within the design period.Studying the corrosion of steel in concrete caused the cracking of concrete protective layer is of great significance to the structural durability design and the maintenance of existing bridges.Concrete,as a multiphase material,has a non-uniform structure at a certain scale.Finding the relationship between microstructure and macroscopic performance is an important issue that materials science and computational mechanics have faced for decades.For bridge structures in the ocean or in harsh environments,the erosion of chloride ions in the environment causes the steel to rust.The rust expansion of the steel will cause the concrete cover to crack or even peel off,which will cause the durability of the concrete structure to deteriorate.Therefore,it is particularly important to accurately evaluate the diffusion process of chloride ions in concrete.Long-term research is also needed on the cracking mechanism of concrete protective layer caused by steel corrosion.In this paper,a multi-scale simulation study on the rust-induced cracking of reinforced concrete caused by chloride ions is carried out.In order to study the rust-induced cracking of reinforced concrete caused by chloride ion diffusion,a concrete lattice model was first established to realize the random placement of aggregates in two-dimensional space.Then,the mechanism of chloride ion erosion and steel bar rusting is discussed.Based on the homogenization theory,the mesoscopic three-phase heterogeneous structure of concrete was established,and the relationship between the mesoscopic structure parameters and the macroscopic effective performance of concrete was studied.Considering the cracking softening effect of concrete,the rust expansion cracking process of reinforced concrete in chloride ion environment is studied based on the chloride ion diffusion model and the steel corrosion expansion theory.A multi-scale modeling method combining the mesoscale and macroscopic scales by the interface transition layer is proposed to ensure the accuracy and efficiency of chloride ion diffusion in multi-scale models.A multiscale model of chloride ion diffusion was established based on Fick's law.The influence of multi-scale interface conversion layer on chloride ion diffusion was studied by analytical derivation and numerical simulation,and the feasibility of the method was verified.In addition,a multi-scale model of reinforced concrete mechanics was established and the effects of different compensation ratios on rust-expanding of reinforced concrete at different locations were studied.In order to simulate the dynamic whole process of rust cracking of reinforced concrete in chloride ion environment and reduce the numerical calculation cost of rust concrete cracking of reinforced concrete,based on the multi-scale model of reinforced concrete mechanics and the multi-scale model of chloride ion diffusion established in the previous chapter,consider the chlorine in concrete.The stress effect of ion diffusion and the renewal of chloride ion diffusion boundary are proposed.The coupling analysis method of rust concrete cracking and chloride ion diffusion is proposed.The numerical simulation results of concrete rust expansion cracking are compared with the results of natural corrosion experiments,and the reliability of the coupling analysis method is verified.In order to study the rust expansion cracking of reinforced concrete in different areas,based on the coupled diffusion analysis method,three kinds of steel bar diameters and five protective layer thicknesses are set in the corner area and the side area concrete.Numerical simulation and comparative analysis of different steel bar diameters and protective layer thicknesses for different areas of steel bars Concrete cracking mode and crack width.