Investigation On Chloride Diffusion Characteristics Of Structural Concrete Under Different Stress

The chloride ion erosion of concrete structures under load is one of the most important subjects in the study of the durability of concrete structures. In the past, scholars have done a lot of research on this subject, and achieved fruitful results. But because of the environmental conditions of durability test are not unified, lacking of tests on chloride ion transport under shear stress in concrete structures and lacking of tests on chloride ion transport under complex load (stress) in concrete structures which meets the actual engineering situation, chloride ion transport research under the action of load in concrete structures is an urgent need to carry out further experimental research, in order to obtain the standard and systematic research results. The main work of this paper can be summarized as:(1) Experimental studies on chloride transport in concrete structures subjected to positive (tensile) stress under standard environmental conditions were carried out. The effect of tensile stress will lead to the formation and development of micro cracks in concrete structures, and accelerate the transmission of chloride ions in concrete. Compared with the existing test results of chloride ion transmission in concrete structures under the non-standard environmental conditions, we can know that the standard of environmental conditions can shorten the test cycle, highlighting the influence of chloride ion transport in the concrete structures which caused by the load, make the test result more accurate and reduce the soaking time which may effect the test results because of the concrete hydration.Finally, the formula of chloride diffusion coefficient of concrete structure under standard environment and positive stress was proposed, and the influence of standard environment and positive stress on chloride transport was analyzed. The tensile stress will increase the chloride diffusion coefficient of concrete structure.(2) A new four point bending shear method was used and the concrete beams were subjected to the action of long term shear load in order to study the chloride transport in concrete structures under shear stress. The shear stress will accelerate the transmission of chloride ion in concrete structures. Combined with the test results and the existing formulas of chloride diffusion coefficient of concrete structure, the formula of chloride diffusion coefficient of concrete structure under standard environment and shear stress was proposed. Finally, the concrete chloride ion transmission in concrete structures under standard environment and shear stress was analysed quantitatively. We can know that the shear stress will increase the chloride diffusion coefficient of concrete structure.(3) The experimental study of the chloride ion transport in the concrete structures under complex stress was carried out. The effect of complex stress on concrete chloride ion transport in concrete structures is caused by the normal stress and shear stress. The normal stress and shear stress in complex stress will lead to the increase of free chlorine ion content in the concrete structure and the increase of the chloride diffusion coefficient of concrete structure in the same way as they are alone. Finally, the mechanism of the effect of stress on chloride transport in concrete structures was described by theoretical analyses and experimental verifications. The existence of normal stress and shear stress will cause the change of stress tensor, so as to change the volume strain of concrete. We introduced two intermediate variables, the porosity and volume strain, to analyze the damage caused by the stress effect on the concrete structure,which will lead to the decrease of the durability of the concrete structures.