Study On Rebar Corrosion Induced By Chloride To Durability Of Underground Structure

Underground reinforced concrete structure in the littoral or the tunnels below the seabed longtimely suffer the corrosion of chloride salts, which leads to the corrosion of reinforcement embedded in concrete and further arouses significantly carrying capacity reduction of structure,and the results of these do damage to the durability of underground structure. Many academicians at home and aboard have carried out extensive research to this question. Based on the existing study achievements,the paper studies the diffusion of chloride ion,predicting models about rebar corrosion,expanding force caused by corrosion productions and so on. the contents are as follows:First of all,the paper investigates the factors influencing the chloride ion's diffusion in concrete structure,including penetrating coefficient,critical concentration,concentra-tion in concrete surface of chloride ion, and thickness of concrete cover. The paper emphasizes main factors influencing chloride ion's diffusion,which includs the bonded ability of concrete,surrounding temperature,humidity,dry-wet circulation and cracks in concrete structure and so on. The mathematical formula is obtained by using the method of multi-factors,and then analysis and calculation is implemented to the four chief influencing factors by matlab.Secondly, the paper summarizes and discusses the mechanism of rebar corrosion and then make some discussion about the chief influencing factors. According to the development of reinforcement corrosion: free expansion stage,expanding force stage and cracking stage of concrete,forecasting formulae based on the quantity of corrosion production is established and then reliability analysis is executed to the model based on the probability distribution of the factors.Thirdly, analysis is performed to the expanding force caused by corroded production with the theory of elastic mechanics and the paper attains the simple calculation expressions in the stage of uncracked concrete and partial cracked concrete respectively. Through the process,the critical length exists in concrete cover,when reaching this length ,because of achieving concrete tension strength,the cracks will quickly connect and get to the surface of concrete cover,which leads to the reliability reduction of concrete structure or element members.Finally,the paper respectively uses the original Fick second law model,the model of Duracrete and the model putted forward in this paper to calculate and analyze the east tunnel below the seabed in XiaMen city. The analyzed results indicate the time at the beginning of rebar corrosion using the first method is shorter than the latter two methods ,the reason is likely that the first model can not consider the influence of surrounding temperature,humidity ,the bonded ability of concrete ,dry-wet circulation and cracks. The first result is about half of the two latter results. The result calculated by the paper's model is approximately the same as that of Duracrete model. the paper's moder comprehensively considers many influencing factors,which further establishes a firm foundation to probability analysis based on reliability of structure.