Numerical Simulation And Experimental Study Of Chloride Transport In Unsaturated Concrete

The problem of durability of concrete structures, such as steel corrosion,protection layer and so on, which are caused by the corrosion of steel and the loss of protective layer, is a common concern in the field of non saturated chloride corrosion.The research and analysis of the transfer process and the transmission mechanism of water and chloride ions in concrete under unsaturated condition, establish the model of water and chloride transport in the environment is very important to the durability of reinforced concrete.First of all, in this paper, the mechanism of moisture transfer in concrete under dry wet alternation is discussed, and the model of moisture transfer under dry and wet alternation is constructed, and the corresponding experiments are carried out. Then system analysis the unsaturated concrete chloride ion transport mechanism,alternation of wet and dry in concrete under water and ion transport mechanism as the foundation, constructs the unsaturated state concrete chloride ion diffusion-convection transfer model and through the dry wet cycling experiment and splash zone simulation experiment is verified. The main research contents and conclusions are as follows:(i)From the point of view of concrete pore microstructure of analysis of concrete moisture is present in various forms, its low permeability and so on, to investigate the moisture transport in concrete is the interaction of water vapor diffusion and liquid water seepage, and pointed out that the water in the drying,wetting process, its transmission rate exist difference and equivalent moisture diffusion coefficients in the presence of hysteresis characteristics, the dry and wet process should be using different diffusion coefficient to describe the alternation of wetting and drying under the action of water transfer.(ii)By alternating wet and dry moisture transmission experiments, the capillary water absorption coefficient, concrete internal relative humidity and moisture transmission rate were studied through numerical simulation of different equivalent diffusion coefficient through the trial, the calculation results show that, transmission model of selecting suitable diffusion coefficient can be used for simulation ofalternating wet and dry under the action of water transport, water transport in transmission rate and depth of influence mainly by the initial conditions, diffusion coefficient, drying and wetting time decision.(iii)The transport mechanism of chloride ion in unsaturated concrete is essentially the coupling process of chloride ion concentration diffusion and chloride ion with the pore solution convection. In this paper, the basic theory of diffusion and convection is introduced, and the effect of moisture transfer is incorporated into the convection of chloride ions.(iv)Chloride dry wet alternate experimental and numerical simulation results show that, both convection chlorine ion peak and the transmission depth increase with dry- wet time is proportional to the increase, alternating wet and dry than full immersion can accelerate the transmission of chloride ion in concrete; splash zone simulation experimental data results show that splash zone chloride content value decreases with the increase of elevation, and in the content of chloride ion in the tidal zone value decreases with the increase of elevation increases, the splash and tidal zone at the junction at the chloride ion erosion is more serious, as concrete durability design and maintenance of the critical region.