Randomness Of Chloride Ion Erosion In Concrete And Service Life Prediction Under Natural Environment

Reinforced concrete structure is a structure form that is most widely applied in engineering. In chloride environment, chloride ions penetrates into concrete that will dispassivate the re-bar in concrete and induces re-bar corrosion. The volume expanding of bar corrosion product in concrete leads concrete protective layer cracking or spalling with corrosion developing, and then durability failure of the concrete structure happens. Predicting service life for reinforced concrete component is a problem that need be resolved urgently, since it can be used for the durability design of reinforced concrete structure, evaluation and maintenance strategies decision.Based on data of chloride penetration of natural specimen and simulated experiments, the main study contents in the paper include:1. Based on data of chloride penetration of natural specimen, randomness of the chloride concentration distribution in existing concrete is studied. Furthermore, using the probability method on the basis of the second Fick's law, the probability characteristics of influence factors on the durability life of concrete structures were carried out, and the probabilistic model of corrosion initiation time of steel bar in concrete in chloride environment is established on the basis of the Fick's second law. By means of Monte-Carlo method, the analysis conclusion shows that the corrosion initiation time of steel bar of background project submits to a lognormal distribution, and its probability density function is given. The statistic parameters of the factors influencing the probability distribution of the corrosion initiation time are all studied.2. Using the Kim model, the rate of steel corrosion and its influencing factors were analyzed, and a probabilistic model of cracking time of concrete protective layer is established. Combined with the probabilistic model, the conclusion shows that cracking time of concrete protective layer of a pier in the project background submits to lognormal distribution, and the probability density function is gotten.3. According to the concrete mix proportion of background project and the test standard in NT Build 433-94, a natural diffusion experiment is designed, and the distribution randomness of chloride concentration in the test concrete is analyzed, and the stochastic model of corrosion initiation time of steel bar in test concrete under the experimental conditions is established. Using Monte-Carlo simulation, the conclusions show that the corrosion initiation time of steel bar submits to a lognormal distribution under the experimental conditions as under the natural environment, but its discreteness is less than that under the natural environment.4. At the basis of the conclusions of the above-mentioned study, the chloride ion erosion model under the experimental conditions is modified. Based on the modified model, chloride ion concentration at the steel bar surface under the experimental conditions and natural environment is all calculated by Monte-Carlo method. There are good linearity relationships between them, and the acceleration factor is 264. Furthermore, service life prediction of background project using test data is realized.5. Each life criteria of concrete structures in chlorine ion erosion environment is analyzed, these criteria include the corrosion initiation time of steel bar, cracking time of concrete protective layer because of corrosion, cracking limitation of concrete protective layer and bearing capacity criteria. Based on the comparative analysis of the randomness of chlorine ion erosion in different environment and steel corrosion situation, the life criteria which apply to concrete structures in the natural environment and the experimental conditions are studied.