Durability Allowance And Life Prediction Of Concrete Box Girders In Chlorine Salt Environment

The durability of concrete structures has become a key issue in engineering field because it involves structural safety,economy and sustainable development.The corrosion of reinforcing steel bar and the shedding of protective layer caused by chloride ion corrosion are the main causes of durability failure of concrete structures.It is very important for durability analysis of concrete structures to explore its transmission process in concrete and establish diffusion models under different erosion conditions.Therefore,based on the traditional diffusion law and the theory of cellular automata,a new cellular automata model for analyzing chloride diffusion process in concrete is established,and the calculation program of the model is compiled with the help of MATLAB software.The correctness and rationality of the model are verified by laboratory tests and relevant literature data.The chloride diffusion process in concrete box girder is simulated and analyzed by using the model,and the durability life of the structure is predicted.Finally,from the point of view of probability theory,a cellular automaton model considering the random diffusion effect of chloride ions is established.Combining with the theory of structural reliability,a prediction method which can effectively predict the durability life of concrete structures is proposed.The main contents of this paper are as follows:(1)According to the transport mechanism of chloride ion in concrete,the heat conduction theory and the law of mass conservation,the chloride diffusion model of chloride ion in concrete with one-dimensional,two-dimensional and three-dimensional diffusion is deduced,and the analytical solution of the model is given.(2)On the basis of chloride diffusion equation,a new numerical calculation method,cellular automata,was introduced to establish the cellular automata models for simulating chloride diffusion in concrete in one,two and three dimensions.The computational program of the model was compiled with the help of MATLAB software.With the help of relevant literature examples,the variation law of chloride concentration in concrete with one-dimensional,two-dimensional and three-dimensional diffusion is analyzed by using the model.The correctness and rationality of the model are verified by comparing the simulated value with the analytical solution of the model.(3)Considering the influence of water-cement ratio,environmental temperature,time-dependent parameters,concrete bonding capacity and external load on chloride diffusion coefficient of concrete,a chloride diffusion model under multi-factor coupling was established.The influence of various factors on chloride diffusion coefficient is analyzed.It is concluded that chloride diffusion rate of concrete increases with the increase of water cement ratio and temperature,decreases with the increase of time dependent parameters,concrete bonding capacity and protective layer thickness,increases with the increase of tensile stress,and decreases first and then increases with the increase of compressive stress.(4)Based on the theory of cellular automata and the chloride diffusion model under multi-factor coupling,a cellular automata model was established to simulate the one-dimensional,two-dimensional and three-dimensional chloride diffusion process in concrete under multi-factor coupling.The correctness and rationality of the model are verified by indoor chloride ion erosion test and chloride ion diffusion model of concrete in relevant literature.(5)The cellular automaton model of chloride ion diffusion process under single factor was used to simulate and analyze the chloride ion erosion process and variation law in concrete box girder of single-track railway,and the durability life of the structure was predicted.By comparing with the analytical solution of life prediction,the correctness and feasibility of this method in predicting the durability life of concrete structures are proved.(6)Durability analysis and life prediction of 32 m standard span double-track simply supported box girder of passenger dedicated line are carried out by using cellular automata model of chloride diffusion process under multi-factor coupling.It is concluded that the chloride ion diffusion effect of concrete box girder is significantly affected by the external load.Under the external load,the distribution law of chloride ion concentration in the section of box girder is consistent with the distribution law of shear lag.(7)Based on probability theory and cellular automata theory,a cellular automata model considering the random diffusion effect of chloride ions is established.Combining with probability theory and structural reliability design theory,a prediction method which can predict the durability life of structures is proposed.The corrosion process of chloride ion in single box and double chamber tied arch bridge is simulated and analyzed,and the durability life of the structure is predicted.The results show that the random diffusion model can effectively simulate the randomness and uncertainty of chloride ion diffusion process,and can reflect the actual erosion process of chloride ion in engineering.