The Mechanism Of Chloride Penetration In Unsaturated Concrete At Coastal Atmosphere Zone

Reinforced concrete infrastructures at coastal atmosphere zone usually suffer chloride corrosion. Protection of steel bars which comes from concrete is continually weakened by chloride so that steel bars are quickly corroded, and the durability of infrastructures is deprived. As a result, the safety of structure is weakean, and then leads to a great number of economic losses. In order to investigate the corrosion degree of steel bars and enhance the durability of structure at coastal atmosphere zone, the chloride penetration mechanism in unsaturated concrete and the methodolgy for estimating chloride content are discussed in this research.Firstly, the chloride penetration mechanism in unsaturated concrete at coastal atmosphere zone is explored. Attenuation models of chloride content for Yantai and Weihai region, China and the World are established by fitting the measured and simulated data of published papers, respectively. The variation of chloride content at coastal atmosphere zone with the exposure time and the distance from seaside is investigated.Secondly, after considering the interaction of diffusion and convection in the chloride mass conservation equation, the change of water by convection in the water mass conservation equation is also calculated, and a new chloride penetration model is proposed based on chloride penetration process within unsaturated concrete and Fick’s first law. The diffusion and convection are strongly coupled in the poposed chloride penetration model. The solution of this new chloride penetration equation is derived by alternating-direction implicit (ADI) finite-difference method. In order to verify the reasonableness and validity of the new chloride penetration model, the results of the new chloride penetration model are compared with another chloride penetration model and experimental data in the published paper. Furthermore, the change of free chloride content in unsaturated concrete with the exposure time, the distance from seaside and the distance from concrete exposed surface is discussed.Finally, Capacity Matix, Transfer Matrix and Chloride Passing Rate Vector are firstly defined, and the control equation of chloride penetration within unsaturated concrete is established based on mass conservation law. Chloride penetration within unsaturated concrete is modeled by ANSYS thermal analysis module. After comparing with the results of the new chloride penetration model and experimental data, the validity of modeling chloride penetration in unsaturated concrete by ANSYS is validated. In addition, a reinforced concrete beam model is established, and the chloride penetration of this beam from three different directions is simulated by ANSYS thermal analysis module, respectively. The variation of the chloride content at the surface of steel bar with the exposure time and the distance from seaside is also analyzed.