Study On Chloride Ion Distribution And Permeability Of Overloading Damaged Concrete Beam Under Chloride Environment

Steel corrosion is one of the main factors that affect the durability of concrete bridges. The main cause of corrosion of steel reinforcement is the erosion of chloride ions, at the humid and hot environment in the coastal areas of South China, this phenomenon is more serious. With the rapid development of China’s highway traffic, vehicle overloading is increasingly serious, often to produce structural damage to the concrete bridge, making the concrete component with the work of crack, to speed up the chloride ion penetration rate. Fiber-reinforced plastic (FRP) reinforcement and steel plate reinforcement is the main method to repair the damaged bridges, which can not only improve the strength and stiffness of the structure, but also slow down the penetration of chloride ions. In this paper, under chloride environment unreinforced and reinforced concrete beams overloading damage chloride content distribution were studied to explore the FRP and steel reinforcement on chloride ion content; In addition, the use of electric flux method with different crack width and depth of concrete test block of chloride ion permeability were studied, analysis the influence of crack size on chloride ion permeability. The main research contents and conclusions are as follows:(1) The chlorine ion content of control beam which was not under wet and dry circles in the chloride environment was 0.017%. And the average chlorine ion content of the undamaged and damaged beams of FRP reinforced which under wet and dry circles for 3 months were 0.047% and 0.054%, while which were 0.09% and 0.108% under wet and dry circles for 6 months. Noticly, the chlorine content near the cracking was up to 0.077% for 3 months. The distribution of chloride ions in steel reinforced beams were similar to the FRP reinforced beams. The results show that the content of chloride ion in concrete beams increased significantly after wet dry cycles, and the chloride content increased with the increasing of dry and wet cycle time. The average content of chlorine in damaged beams is slightly larger than that of undamaged beams. The penetration of chloride is greatly increased near the cracking, but has no significantly influence to the surrounding concrete.(2) The content of chloride ion in the middle of the cross section of concrete beam is mainly affected by the permeability the bottom, and the content of chloride ion in both sides of the concrete beam is influenced by the permeability both from the bottom and the sides. For FRP reinforced beams which was damaged, under 3 months wet and dry cycles, the average content of chlorine ions in the middle and the both sides of the cross-section were 0.047% and 0.088%, while which were 0.09% and 0.185% under wet and dry cycles for 6 months. For steel reinforced beams which was damaged, under 3 months wet and dry cycles, the average content of chlorine ions in the middle and the both sides of the cross-section were 0.073% and 0.144%, while which were 0.114% and 0.198% under wet and dry cycles for 6 months. Whatever the FRP or steel reinforced beams, the chloride ion content in the middle of the cross-section are significantly lower than the both sides, which indicate that the bottom reinforcement can effectively hinder the penetration of chloride ions from the bottom. Compare with FRP and steel reinforced beams, to the both sides and the middle of the same cross-section, the chlorine content of the FRP reinforced beams are slightly less than that of steel reinforced beams, which due to the FRP reinforced is a paved form but the steel reinforced is a non-paved form. This indicate that the reinforced form affect the penetration of chloride ion.(3) By electric flux method with cracks specimens chlorine ion flux assay, the results show that when the constant crack depth, crack width in the range of 0.1-0.4mm, chloride ion diffusion coefficient with increasing crack width of presentation after first increased and then decreased; when the crack width unchanged, in the range of crack depth 10-25mm, chloride ion diffusion coefficient with increasing crack depth increases, increases linearly.