Study On Chloride Transport In Concrete Under Dry-Wet Cycles

Since chloride erosion is one of the major problems that affect the durability of reinforced concrete structures under dry-wet cyclesand it causes long-term and extensive attention at home and abroad, it is of great importance to study on the chloride transport mechanisms, develop proper models and compute the distribution of chloride in concrete, to extend the service life of infrastructure, and improve the economic benefits of infrastructure. Numerical computation method is established to simulate the process of moisture diffusion and chloride transport. The main contents and conclusions are shown as follows: 1. The basis theory of chloride transport model under dry-wet cycles is summarizedMechanisms of chloride into concrete are introduced, domestic and foreign research status is reviewed also. According to the transport method of chloride under certain conditions, two computation model of chloride transport under dry-wet cycles are proposed.They are chloride transport model under capillary absorption, and chloride transport model under capillary absorption and ion diffusion. Related parameters of the two models are introduced, laying a foundation for the establishment of numerical method. 2. Radial basis function meshless method of chloride transport in saturated concrete is establishedFirstly, radial basis function meshless method is introduced briefly, radial basis function and collocation method are summarized respectively. Secondly, domain decomposition method is introduced. In this thesis, domain decomposition is used in time domain.In the end, combine radial basis function meshless method and domain decomposition method, and write matlab programs to simulate the chloride transport in saturated concrete. One-dimensional homogeneous problem, one-dimensional inhomogeneous problem, and two-dimensional homogeneous problem are researched respectively. Numerical solution and analytical solution are compared, and the results demonstrate this method has a high accuracy. 3. Moisture distribution in concrete under dry-wet cycles is simulatedCombine radial basis function meshless method and domain decomposition method, and write matlab programs to simulate the moisture distribution in concrete under dry-wet cycles. Firstly,homogeneous diffusion problem is researched, and three times dry-wet cycle process is simulated. Pictures of moisture varying with position at different times and pictures of moisture varying with time at different positions are plotted using matlab. The results of pictures show obvious law of dry-wet cycles. Then extend the time of dry-wet cycles and diffusion depth of model respectively. And moisture distribution law under dry-wet cycles is researched further. The computation results demonstrate that the moisture will gradually tend to a stable value after extending the time of dry-wet cycles.Finally, the effect of moisture varying to moisture diffusion coefficient is considered. Moisture distribution results of constant coefficient model and variable coefficient model are compared. The computation results demonstrate that the effect of moisture varying to water diffusion is obvious. 4. Chloride erosion process in concrete under dry-wet cycles is simulatedCombine radial basis function meshless method and domain decomposition method, and write matlab programs to simulate the chloride concentration distribution in concrete under dry-wet cycles.Two models of chloride transport under dry-wet cycles are researched. They are chloride transport model under capillary absorption, and chloride transport model under capillary absorption and ion diffusion. For the first model, homogeneous problem is researched firstly,and three times dry-wet cycle process is simulated.Secondly, the effect of moisture varying to chloride transport is considered. Chloride concentration distribution results of constant coefficient model and variable coefficient model are compared. The computation results demonstrate that moisture varying has a positive effect to chloride transport.For the second model, one-dimensional homogeneous problem is researched firstly. Secondly, the effect of capillary absorption impact factor to chloride transport is researched. The computation results demonstrate that the bigger the value is, the more obvious its effect on chloride transport is. Lastly, the effect of time to chloride transport is researched. The computation results demonstrate that when time-dependent chloride diffusion coefficient is considered, transport velocity of chloride in concrete will reduce.