Transport Mechanism Of Chloride In Concrete And Corroded RC Expansion Model

The chloride attack is always regarded as an important cause of deteriorate in service performance of reinforced concrete structure (RC). Because of the significant influences of loading and cracks of concrete on chloride penetration, the study of chloride transport mechanism subjected to loading and cracks, as well as concrete rust expansion cracking process, play a great significant influence on the accurate prediction of service life. The service life of concrete structure can be divided into three phases:inductive phase, development phase and destruction phase. Thus, present work makes it as a major line, focusing on the mechanism of loading and cracks in the inductive period, and establishing the prediction model of corrosion expansion of reinforced concrete in development phase. The main research works as follows:By designing of a device for sustained loading on reinforced concrete beam, the chloride solution immersion tests are carried out for ordinary concrete beams and slag cement concrete beam subjected to different loadings tests, analyzing the influences of loading and binding capacity on chloride ion transport. By proposing a model considering the influence of loading on chloride ion diffusion coefficient, and determining the parameters in model, and introducing of chloride binding factor and temperature coefficient, the analytical Fick’s second law is modified. The model calculation is consistent with experimental results, and it can be used to predict the transport of the chloride ion in concrete subjected to soaking conditions and loadings.Through decomposing the driving force of chloride ion transport subjected to wetting-drying cycles into convection and diffusion, and through considering the difference of the diffusion coefficient of water in the dry and wet process, the relationship between moisture diffusion coefficient and saturation is established, and through considering the combination of chloride ion, temperature influence and loading influence coefficients, the model of chloride ions subjected to wetting-drying cycles and loading is established, with programming of the corresponding Matlab program for solving the transport equation of the chloride ion in concrete. In order to accurately control the boundary conditions of the wetting-drying cycles, a fully automatic wetting-drying cycles test system is designed, and combined with the artificial simulation of environmental chambers, test study is carried out on the influence of wetting-drying cycles and loadings on concrete beam. When comparing the numerical results with experimental results, it can verify the reliability of the numerical model for better reflecting the pull and pressure loading on the transport of the chloride ion. Through analysis the mechanism of cracks in chloride ion transport, a dual porosity media model for cracked concrete considering the chloride ion transporting in soaking conditions is established, and the methods are proposed of generating the specimens with real cracks and effective determining the chloride ion concentration around cracks, and through conducting an experiment study, it verify the established theoretical model.Using the discrete crack model, it better reflects the distribution of the chloride ion concentration around cracks, as well as on the influence of partially corrosion of reinforcement. Through combining the mechanical theory of hydrodynamics and capillary, which are used to describe the wall face of the capillary absorption and the crack area of the cracked concrete, the model of chloride transport in the cracked concrete in the wetting-drying cycles is proposed. The experiment test of chloride ion concentration in cracked concrete subjected to wetting-drying cycles is studied, and the Energy-Spectrum Analysis Technique of the electron probe is used to determine the concentration of chloride ions of concrete cracked zone. It was found that gradient of chloride ion concentration exist in the concrete cracks, and the depth of the convection zone is approximately20mm-40mm, which verified by the numerical results, reflecting that the characteristics of experimental data and calculation results are in good agreement. Parameter analysis also reveal that the crack width, roughness of cracks, the ratio of length and width and boundary conditions of the drying process can affect the chloride ion concentration distribution in the crack.Based on the concrete anisotropic damage and softening damage of concrete, and considering the elastic behavior of the corrosion products, steel and corrosion products, the porosity in steel-concrete interface transition zone and the filling effect among cracks-corrosion products-concrete, three-phase medium model is established. Through pasting the strain gauge directly on the concrete cross section, the strain variation in the process of steel corrosion in concrete is conducted, and corresponding relationship between corrosion rate and concrete strain is established too, and through comparing the model calculation results with the experimental results, it is found that it can greatly predict the cracking of the concrete, and found that the concrete ring is a good indicator for the evaluation of concrete cracking strain, together with the analysis of model parameters.