Study On The Effect Of Cracking On The Durability Of Concrete Structure In Chloride Environment

Concrete structure is the most widely used in the world at present. Because the concrete has a high compressive strength and low tensile strength, concrete structures work with cracks in practical applications. But now, the influence mechanism of concrete crack on reinforcement corrosion and the significance in limitation of the maximum crack width in concrete structure are always in dispute. Therefore, it is necessary and scientific to study the effect of cracking on the durability of concrete structure.Reinforced concrete slab specimens with transverse crack were designed, and the effects of concrete crack on the permeability of reinforced concrete specimens in chloride environment, steel corrosion rate and length were emphatically studied in this paper by the863program "study on the test and strengthening technology for heavy load railway bridges and road-bed-sub-project3:durability study for bridges under coupling action of environment and heavy load", which is funded by Ministry of Science and Technology of China (301727005). Main results are as follows:(1) Through the testing and analysis of the distributing rules of chlorine ion content on cracks of concrete structure, this paper draws the conclusions that chloride diffusion on cracks is mainly two-dimensional diffusion, and chlorine ion content is significantly higher than other uncracked-sections, when at the same position, chloride ion content increases with the increase of crack width whereas chlorine ion content on section reduces with the increase of the distance between the section and splitting section.(2) This paper used the smeared crack model and the principle of flow balance to simplify study transmission process of chlorine ion in cracked concrete structure, and the results showed that crack has very significant effect on the equivalent chloride diffusion coefficient, and the equivalent chloride diffusion coefficient of cracked concrete is one order or two orders of magnitude less than that of uncracked concrete; and chloride diffusion coefficient in fractures under chloride dry-wet cycling conditions is larger than in free solution.(3) Through90days’s monitoring of reinforcement corrosion current density on cracks of concrete structure, this paper drew the conclusion that corrosion current density is not a constant. Instead, it has an obvious time-varying characteristic which can be divided into three stages:the rising stage of corrosion sprouting period, the falling stage of corrosion development period and stable stage. Whether corrosion sprouting period or corrosion development period, reinforcement corrosion current density increases with the increasing of crack width, water-binder ratio and reinforcement diameter, and reduces with the increasing of concrete cover thickness.(4) This paper has analyzed steel corrosion length in fractures and established the prediction model of steel corrosion length in fractures in which concrete strength, cover thickness, the transverse crack width and reinforcement diameter were considered. Through the verification of an experiment, the analyzed value and the experiment value are inosculated, and the model can be used to predict steel corrosion length in transverse crack area.