Study On Concrete Durability And Service Life Prediction Based On Chloride Corrosion

Durability failure of reinforced concrete structures due to chloride corrosion often occurs, which leads to enormous economic loss, so the durability problems of structures in chloride corrosion environment arouse the attention of people. Chloride corrosion can not only cause the rust of rebar, but also aggravate surface scaling of concrete in cold region. Therefore, the study on chloride diffusion properties in concrete and frost-salt resistance of concrete have very important significance to the durability of reinforced concrete structures in chloride corrosion environment.The chloride diffusion properties in fly ash concrete of marine underwater region, marine tidal region, marine atmospheric region and cold region were investigated by tests. The chloride diffusion model in fly ash concrete was established, and service life prediction for concrete structures in chloride corrosion environment was carried out based on reliability theory. The frost-salt resistance and quantitative design on frost-salt resistance of fly ash concrete were also investigated by tests. The main contents of this paper are as follows:Marine underwater region and marine tidal region are the key region where concrete structures suffer chloride corrosion. The diffusion properties of free chloride and total chloride and the chloride binding properties in different water-binder ratio and different volume of fly ash concrete were investigated by using full-immersion method and alternation of wet-dry method to simulate marine underwater region and marine tidal region respectively. The relationship between free chloride content and total chloride content in concrete was obtained, and the relation model between effective chloride diffusion coefficient and apparent chloride diffusion coefficient was also established. Regression analysis on experiment data was carried out by using linear binding mechanisms, Langmuir binding mechanisms and Freundlich binding mechanisms respectively, and the parameters were obtained. The study above provide basis for describing the diffusion properties of chloride in concrete completely and accurately.The concrete structures in marine atmospheric environment suffer the dual action of chloride corrosion and carbonation. The influence of carbonation on diffusion of free chloride and total chloride in concrete was investigated by using alternation of immersion and carbonation method to simulate marine atmospheric region. The results show that, carbonation action increases the diffusion speed of chloride in concrete.The concrete structures in marine environment of cold region and deicing salt environment suffer the dual action of freeze-thaw and chloride corrosion, freeze-thaw action can increase the diffusion speed of chloride in concrete, and chloride corrosion can aggravate surface scaling of concrete. The influence of freeze-thaw damage on diffusion of free chloride and total chloride in concrete was investigated by full-immersion tests of the concrete with different freeze-thaw damage, and the relation model between chloride diffusion coefficient and freeze-thaw damage was established by introducing freeze-thaw damage value of concrete, which provides basis for establishment of chloride diffusion model in concrete under the environment of freeze-thaw and chloride corrosion.Accelerated frost-salt tests of fly ash concrete were also carried out. The influence of water-binder ratio, volume of fly ash and air-entraining content on frost-salt resistance of concrete were investigated. The variation rule of surface characteristics, weight loss rate, relative dynamic modulus of elasticity, supersonic velocity, compressive strength of concrete with the number of frost-salt cycle were inspected. The relation model between dynamic modulus of elasticity and velocity of ultrasonic sound, and the relation model between dynamic modulus of elasticity and compressive strength of concrete was established respectively. And the model for predicting the cycle number of frost-salt resistance of concrete was also established. The study above provide basis for design of mix proportion of the concrete with request of frost-salt resistance in engineering construction, and also provide basis for the evaluation on freeze-thaw damage and the durability design of concrete structures in marine environment of cold region and deicing salt environment.Based on Fick's second law and the analysis for the influence of temperature, humidity, time-dependence of chloride diffusion, chloride binding properties and freeze-thaw damage on chloride diffusion in concrete, comprehensive chloride diffusion model was established respectively according to different chloride binding mechanisms. The model is reasonable according to engineering verification, which provides theory basis for durability life prediction of concrete structures in chloride corrosion environment.Based on the analysis for probabilistic characteristics of concrete cover, critical chloride concentration, surface chloride concentration, initial chloride concentration, chloride diffusion coefficient, attenuation index of chloride diffusion coefficient and chloride binding coefficient, service life prediction for concrete structures in chloride corrosion environment was carried out according to reliability theory. Meanwhile, the sensitivity of durability life of concrete structures was analyzed, the rule and the degree of influence of each factor on durability life were obtained, which provide reference for durability design of structures. Finally, the durability life of concrete structures under different chloride binding mechanisms were compared. The results show that, Langmuir binding mechanisms can predict service life of structures more accurately.