Pitting Corrosion Of Rebar And Bearing Capacity Of Rc Members Under The Action Of Chloride Ion And Bending Loads

The durability of reinforced concrete structures in chloride environment is always the important problems in engineering field at home and abroad. The vast majority of RC structures in practical engineering are subjected to the coupled effect of loads and environment. Hence, the influence of chloride and bending loads on the durability of RC structure is one of the main directions in terms of durability research.Based on the Fick’s second law and the Monte Carlo method, and the test results of chloride ingress in concrete in the artificial climate salt spray environment and the natural marine environment, the chloride ion diffusivity in concrete, corrosion of reinforcement and the bearing capacity of concrete members under the common action of chloride and bending loads were studied. The main research content and conclusions are as follows:1. According to the test results of chloride ingress under the different bending loads in the artificial climate salt spray environment and the natural marine environment, the random characteristics of the free chloride ion concentration, critical chloride ion concentrations, chloride ion diffusion coefficients, thickness of the convection zone and the concrete cover under the different environments and different bending load levels were analyzed respectively.2. The load influence coefficient of chloride diffusion coefficient f??? was introduced, and the relationship between the bending loads and chloride ion diffusion coefficients and its empirical coefficient of m under the artificial climate salt spray environment were analyzed. The test results indicated that the bending load levels and chloride diffusion coefficients can be better described by the quadratic function; the empirical coefficient m of chloride ion diffusion coefficients will increase with the increasing of bending load level. On the basis above, the model of chloride ion diffusion was established by considering the time-dependent characteristics of diffusion coefficients of chloride ion and bending load level.3. The random prediction model of the maximum corrosion pit depth and the corrosion pitting area of steel bars that considering the time-dependent characteristics of diffusion coefficients of chloride ion and bending loads was derived; the calculation model of the flexural bearing capacity of RC members based on the rust pit of rebars was analyzed. Besides, according to the corrosion tests results of RC members in the artificial climate salt spray environment, the prediction model of characteristic parameters of bar pitting corrosion and the calculation model of the flexural bearing capacity of RC members were verified. According to the Monte Carlo method, the probability density function and random distribution characteristics of the maximum corrosion pitting depth and the corrosion pitting area of bars in the artificial climate environment were simulated and analyzed. The results show that the maximum corrosion pitting depth and the rust pitting area of steel bars are in accord with a normal distribution; the frequency distribution, the probability density and probability distribution of the flexural bearing capacity of RC members based on the rust pit of steel bars can be simulated.4. The sensitivity of the major factors that includes cover ohmic resistance, thickness of the convection-zone, thickness of concrete cover and the chloride diffusion coefficients on the maximum corrosion pitting depth and the corrosion pitting area of bars under the action of chloride salt together with the bending loads were analyzed. The conclusions show that thickness of concrete cover is the highest sensitive influence factor.5. Based on the Monte Carlo method, the influence of thickness of concrete cover on the maximum corrosion pitting depth and the corrosion pitting area of steel bar and the flexural bearing capacity of RC members in the artificial climate environment were analyzed. The results indicate that the durability of concrete can be improved by increasing the thickness of concrete cover. With the increase of concrete cover thickness from 5 mm to 20 mm, the maximum corrosion pitting depth of steel bars is reduced by 25.756 %, the corrosion pitting area of bars is reduced by 40.796 %, and the flexural bearing capacity of RC beams is increased by 68.803 %.6. The calculation results given by the Monte Carlo method show that the chloride diffusion coefficients obviously influenced the maximum corrosion pitting depth, the corrosion pitting area of steel bars and the flexural bearing capacity of RC members. For example, under artificial climate environment, the maximum corrosion pitting depth of steel bars is increased by 17.396 %, the corrosion pitting area of rebars in RC beams is increased by 39.236 %, and the flexural bearing capacity of RC beams is reduced by 55.919 % along with the growth of chloride diffusion coefficients from 20×10-12 m2/s increase to 60×10-12 m2/s.