Research On Chloride Ion Transport Behaviour And Model Of Concrete Under Coupling Of Fatigue Load And Environment

Service potency degradation of cement concrete caused by chloride ion erosion becomes one of the major problems affecting the durability of concrete.The load and external environment are the main factors influencing the chloride ion erosion resistance.It is significant to study chloride ion transport rules and establish corresponding transport model of cement concrete under the coupling of fatigue load and environment.Therefore,chloride ion transport behavior of concrete was studied through the combination of experimental study and theoretical modeling,the main research contents and innovative results are as follows.The influence of sulfate solution concentration and fatigue load(stress level,load frequency,solution concentration)on the chloride ion transport behavior of concrete was studied by selecting mechanical corrosion fatigue test device,formulating perfect testing scheme,using test methods of chloride ion concentration and erosion depth.Time dependency of apparent surface chloride ion concentration and diffusion coefficient was investigated.Time dependency model of apparent surface chloride ion concentration was vertified,also the influencing factors of s Tab.value and cumulative rate coefficient was analyzed.The deteriorating law of concrete resistance to chloride ion permeability was studied by introducing effect coefficient K on the basis of the apparent diffusion coefficient.According to the concrete fracture mechanics and damage mechanics theory of chloride ion diffusion coefficient model under fatigue load was established and amended through the steps of the division of the chloride ion diffusion path,diffusion coefficient characterization based on the factor of crack and fatigue load parameters introduced.The effects of model parameters such as stress level to chloride ion migration rate were analyzed.Concrete chloride ion transport model under fatigue load was established according to the transmission mechanism and fatigue cumulative damage theory,also the model analytical solution was given.The rationality of the model was validated through the laboratory test.The influence of the stress level,load frequency,temperature,etc to chloride ion erosion rule of concrete was analyzed.Chloride ion transmission law of unsaturated concrete under fatigue load was investigated through perfect experiment design and parameter optimization.The influence of dry wet system and stress level to the chloride ion concentration,erosion depth,surface chloride ion concentration and its time dependency was analyzed.Through fitting of surface chloride ion concentration time dependency,the result shows that the exponential model is fitting well.Through analysis on time dependency of the diffusion coefficient and influencing factors of K,the deterioration of resistance to chloride ion permeability of concrete is obvious under the high stress level of fatigue load.According to the chloride ion transmission mechanism,the chloride convection-diffusion control equation in unsaturated concrete was derived by considering the difference of moisture transmission the dry-wet alternate process.The fatigue load moisture influence coefficient equation was given on the basis of fatigue load diffusion coefficient model.Water transport equation and chloride ion transmission control equations under the coupling of fatigue load and dry-wet alternating was obtained according to concrete chloride ion convection diffusion control equation under dry-wet alternate cycling.Crank-Nicolson method was engaged to develop the finite difference format of equation above and MATLAB software programming was used to get the numerical solution.The result shows that the laboratory test results have a good correlation with the measured.The influence of stress level,load frequency,temperature and initial saturation to the chloride ion distribution rule and convection zone depth of concrete was analyzed.Compared with concrete chloride ion transport law under the pure dry-wet alternate cycling,the chloride ion concentration in each layer and convection zone depth increases obviously with the introduction of fatigue load.