Stochastic Prediction Method Of Steel Bar Pitting Corrosion In RC Structures Under Chloride Environmen

As the extension of service time, and there are much more durability failure of the concrete structure happening. The durability of concrete structures becomes one of the most concerned issues in the modern world of engineering. And the chloride ion corrosion is one of the main factors of leading to insufficient durability of concrete structures.Based on the result of concrete erosion indoor and in the natural chlorine salt environment, the related problems on prediction of characteristics of volume of steel bar rust pitting have been studied. The main study contents and conclusions in this study as follows:1. Based on the result of concrete erosion indoor and in the natural chlorine salt environment, the relation between diffusion coefficients of chloride ion in concrete and erosion time was studied, and the stable time of diffusion coefficients of chloride ion of concrete under different erosion environments have been analyzed. 2. The attenuation rate of diffusion coefficients of chloride ion in concrete V was introduced, and the relation between the attenuation rate of diffusion coefficients in concrete in the artificial climate environment or natural tidal environment and the erosion time was respectively analyzed. The results show that the attenuation rate of diffusion coefficients of chloride ion quickly reduced with the increment of the erosion time. The influence of the water-cement ratio, curing time and environmental factor on the attenuation rate of diffusion coefficients of chloride ion was analyzed; the results also indicate that the influence of environmental factor was the largest factor.3. The forecast model of the steel bar’s corrosion pitting depth and the corrosion pitting area was established, and the random prediction model that considering the degeneration of diffusion coefficients of chloride ion was derived. Also, according to the corrosion test results of concrete in the artificial climate environment and natural tidal environment, the theoretic model was reasonable. The influences of the major factors that cover ohmic resistance, environment temperature, thickness of concrete cover, thickness of the convection-zone and critical chloride concentration on the steel bar’s corrosion pitting depth and the corrosion pitting area were analyzed. The results indicate that the most important influence factor were the thickness of concrete cover.4. According to the erosion results of the indoor test of concrete and the test and existing concrete in the natural marine environment, the random characters of the free chloride ion concentrations of concrete, peak of free chloride ion concentrations, thickness of the convection-zone, diffusion coefficients and thickness of concrete cover in different environmental conditions were analyzed.5. Based on the Monte Carlo Method, the Probability distributions of the steel bar’s corrosion pitting depth and the corrosion pitting area in artificial climate environment were simulated and analyzed. Also, the characters of the steel bar’s corrosion pitting depth and the corrosion pitting area that considering the degeneration of diffusion coefficients of chloride ion were analyzed. The results show that the steel bar’s corrosion pitting depth and the corrosion pitting area are related to the degeneration of diffusion coefficients of chloride ion. The steel bar’s corrosion pitting depth which considering the degeneration of diffusion coefficients of chloride ion is2times of the steel bar’s corrosion pitting depth which assuming the diffusion coefficients of chloride ion is constant, and the corrosion pitting area which considering the degeneration of diffusion coefficients of chloride ion is more than3times of the corrosion pitting area which assuming the diffusion coefficients of chloride ion is constant eg.6. According to the Monte Carlo Method, the influence of thickness of concrete cover on characteristics of volume of steel bar rust pitting of concrete members in the artificial climate environment and natural tidal environment was studied. The results indicate that the characteristics of volume of steel bar rust pitting of concrete reduced with increase of thickness of concrete cover. The thickness of concrete cover average from15mm to25mm, the maximum steel bar’s corrosion pitting depth of concrete members under artificial climate environment was reduced by44%of original, and the corrosion pitting area of concrete members under artificial climate environment was reduced by55%of original eg.