Study On Chloride Erosion In Concrete Under Freeze-thaw Cycle

It has been a growing concerned problem in the field of civil engineering that the interaction of freeze-thaw cycle and chloride ion erosion cause the lack of durability of the reinforced concrete structures which lead to considerable economic loss and a huge waste of energy.Therefore,it is of great significance to deeply understand the chloride ion erosion process and study on the mechanical behavior of concrete under the influence of freeze-thaw cycle for extending service life of reinforced concrete structures and improving the efficiency and cost-effectiveness of engineering facilities.This study is based on chloride ion transport process in the water-contained concrete under the influence of freeze-thaw cycle.The main contents and conclusions are shown as follows:1.The basic theory of chloride ion penetration in concrete under freeze-thaw cycle is summarizedThe erosion mechanism of chloride ion in concrete is described in this part and the domestic and foreign research status of chloride ion transportation and freeze-thaw cycle is reviewed.Coupled thermal stress analysis in the thermal simulation analysis theory and differential equations of heat conduction theory are also introduced.Secondly,the equation of chloride ion penetration in concrete is derived under the influence of several factors in practical engineering such as diffusion depth,combined capacity of hydration,degradation effect coefficient of chloride ion diffusion in concrete and environment temperature.The studies make a significant contribution in chloride ion penetration in concrete under complex conditions.2.The temperature field of freeze-thaw cycle and volume change of water are studiedFreezing and melting process of water is simulated under the consideration of thermal stress simulation theory and transient heat conduction analysis.By changing the temperature boundary condition and the setting of thermal expansion coefficients in the different temperatures,change process of temperature field under freeze-thaw cycle and volume change of model in phase change simulation are studied.The theoretical results are compared with a lot of actual results in order to determine reasonableness of finite element simulation and build foundation for subsequent study of water under freeze-thaw cycle in pores.3.The damage evolution in concrete under freeze-thaw cycle is simulatedThe freezing process of pore water which leads to the damage of mechanical properties in concrete under freeze-thaw cycle is introduced and the research methods about concrete failure mechanism under freeze-thaw cycle are elaborated.The damage area evolution and temperature field distribution in concrete which caused by frozen expansion of pore water under the influence of cooling process and freeze-thaw cycle are simulated in the Abaqus software platforms.According to the temperature field and injury results,it is explained that surface-off and internal crack expanding phenomenon in concrete structures occur after freeze-thaw cycle test using the fast-freezing method.All the research provide the theoretical evidence for studying on the failure of bearing capacity of concrete structures.4.The chloride ion penetration in concrete under freeze-thaw cycle is studiedThe diffusion of chloride ion under the natural conditions is studied.The diffusion models are chosen to simulate under unchanged temperature in order to compared with change process of temperature field under freeze-thaw cycles.The simulation of chloride ion diffusion based on the concrete damage under freeze-thaw cycle is researched and the results are used to compare with chloride diffusion process in the non-damaged concrete model under natural conditions.The research aims to study on the influence of chloride ion diffusion based on concrete damage under different freeze-thaw cycles.The process of chloride ion erosion in damaged concrete under freeze-thaw cycles is simulated.The results show that the diffusion velocity of chloride ion in damaged concrete is greater than that of chloride ion diffusion in concrete without freezing-thawing damage,and the damage of freeze-thaw cycle in concrete has a remarkable acceleration effect on chloride ion erosion.