Research On The Relationship Between Cracks Of Concrete And Steel Corrosion In Concrete In Chloride Erosion Environment

At present the research on the durability of concrete is mostly based on the sound concrete which has no cracks. However, for the concrete structures in real engineering, because of the influence of environmental factors and external load, it is hardly to avoid some macroscopic or microscopic cracks in concrete materials. Therefore, it has notable theoretical significance and practical value to study the influence rules of crack on the durability of concrete structures. In view of the issue on the durability of the cracks concrete with chloride erosion environment, according to the program of Youth Foundation of Hubei Provincial Department of Education named as “analysis of crack control of fuzzy reliability of concrete structure on general atmospheric environment”, the durability theory and experimental study of the concrete crack which on chloride erosion environment were emphatically discussed in this paper. The research results can provide theoretical evidence for the revision of concrete structures cracks limit standards in chloride erosion environment, and theoretical basis for the durability reliability assessment of concrete structures with cracks. The main research results are as follows:(1) Through the detection and analysis of chloride ions content around the area of cracks under the effect of dry-wet cycles, with the increase of distance from crack, the concentration of chloride ion in concrete gradually reduced; the crack width is too larger that the transportation of chloride ion in concrete was characterized by two-dimensional diffusion. With the increase of the crack width, two-dimensional chloride ion diffusion region around the crack effect is more conspicuous; it can be knows according the concentration distribution of chloride ion around the cracks: the influence diffusion depth of chloride ion in regional around the cracks is approximately 30~50mm.(2) Combined with the distribution rules of chloride ion concentration on cracks in different depth of the concrete structure it can be found out that: the concentration of chlorine ion in the region of the crack tends to be stable after depth of 35 mm. In the stable period, the concentration of chlorine ion increases with the increasing of the crack width. Comparison of the distribution rules of chloride ion concentration on cracks and on region around the cracks in different depth of the concrete structure, it can be shown that the effect of crack width on the transportation of chloride ion on cracks of concrete is more notable, and the impact on region around the cracks is gradually reduced.(3) The relationship between the crack and chloride ion diffusion rate were studied. The results of the study show that: Since the presence of cracks, the influence on the equivalent concrete chloride ion diffusion coefficient is very significant. With the increase of the crack width, the transmission rate of the chlorine ion is stronger. When the crack width of w=0.2mm, the chlorine ion diffusion coefficient of cracked concrete is 3-4times of the sound concrete. When the crack width of w=0.8mm, the chlorine ion diffusion coefficient of crack concrete is 8-10 times of the sound concrete. Adopting the dual porosity medium model to analyze the transport of chloride ion on cracks of concrete, the relationship between chloride ion diffusion coefficient and crack width can be regressed as the cubic function.(4) A multiple linear regression analysis with steel corrosion length which considered a number of factors was performed by MATLAB software. It was found that according to the influence degree, the main influence factors of corrosion of reinforcement length are crack width, the thickness of protection layer and bar diameter. Among all the influence factors the influence of bar diameter is very small. Therefore, a prediction model of steel corrosion length on cracks of concrete structure was established by considering the horizontal crack width and the thickness of concrete cover.(5)The fuzzy reliability of crack control of concrete structures under chloride corrosion environment is studied.According to the concept of the guarantee rate in the formula of transverse crack width,a random calculation model of the maximum transverse crack width of the reinforced concrete structure members is established.According to pre experimental research results which concerning the influence of transverse cracks on durability damage of concrete structures,The comprehensive membership function of the maximum value of the transverse crack width, one new membership function model which considered the maximum crack width,average transverse crack width and protective layer thickness is set up. Based on this, the fuzzy reliability analysis of the crack control of concrete structures under the environment of chloride corrosion is carried out.