Randomized Study Of The Important Durability Parameters Of Concrete Under Chloride Environment

The durability is one of the most important issue of concrete structures design. Furthermore, the corrosion of chloride ions is a main influencing factor of insufficient durability of concrete,. The corrosion of chloride ions damages the passive film of re-bars in concrete, which leads to corrosion of re-bars and shorten the service life of concrete structures.Based on natural environmental and simulated environmental tests of chloride ion corrosion, characteristics of chloride erosion in concrete, the stochastic characteristics of some important durability parameters, such as thickness of the convection-zone, have been studied under cyclic wetting and drying conditions. The work above is of some reference significance for further research on randomization and durability of chloride ion corrosion concrete under cyclic wetting and drying conditions.According to the concrete chloride ions corrosion tests and the existing statistical analysis of the tests, the main conclusions of this study are obtained as follows:(1) Under cyclic wetting and drying conditions, there are obvious convection-zone both in indoor artificial climatic environmental conditions and natural environmental conditions. The thickness of the convection-zone is generally less than10mm. Factors such as water-cement ratio, initial curing time, mineral admixtures (fly ash), loading and coupling of load and carbonation, have a certain influence on the thickness of the concrete convection-zone, which is however not obvious.(2) The improved natural diffusion method is applied to simulate the convection-zone under the field expose condition. The test results show_that the concrete surface chloride ion concentration and chloride ion diffusion coefficient obeys the lognormal distribution, whereas the peak chloride concentration and the convection-zone thickness both obey normal distribution.(3) The concrete cover depth, threshold chloride content and chloride ion diffusion coefficient have prominent influence on initiation time, while the influence of the peak chloride concentration and convection-zone thickness on initiation time is relatively low.(4) Making use of the results of the improved natural diffusion method tests and field expose tests, the chloride ion concentration of convection-zone is written as a logarithmic function with the independent variable of depth. A program model based on BP neural network method is given to predict the chloride ion concentration at different depths of the concrete. By training and simulation, the pridiciton results of the model are close to the measured ressults.(5) On the background of strong tidal estuary environment of the Qiantang River, the results of the correlation of indoor artificial-climate accelerated tests, improved natural diffusion method tests and field expose tests are analyzed. The results indicate that indoor artificial-climate accelerated tests and improved natural diffusion method tests have a good similarity with field expose tests.