Research On Similarity Of The Chloride Ingress In Concrete Under Natural And Artifical Simulation Environment

Abstract:Corrosion of reinforcement caused by chloride ingress is the main reason for durability deterioration of reinforced concrete structures exposed to chloride environment, and it is very significant to accurately forecast the life and durability of concrete construction by establishing the similarity of the chloride ingress into concrete under natural and artifical simulation environment. However, the precondition is to establish the corresponding test procedures of artifical simulation environment, which can ensure the rationality of the similarity into the process and mechanism aspect. Key work is to solve the basis of the test parameters including temperature, humidity, wetting-time, wind speed and test time. There are many shortcomings of the traditional relevant research, and the reuslts are difficult to compare each other. Based on the conclusions studied by others, the concept of the internal micro envrionment in concrete was studied in this paper, and the test procedures of the artificial simulation environment test system were established. In this connection, the similarity realtion of the chloride ingress in concrete under the natural and artificial simulation envrionment was decuced. The detailed content is as following:(1) Based on the concept of the internal micro environment in concrete, the action spectrum and response spectrum models of the macro and micro envrionment were deduced in forms of piecewise form. Similarities and differences of the natural and artificial simulation environment were investigated, and the traditional concept regarding the natural envionment as the internal micro envrionment in concrete was abandoned. By discussing the diference of the relative humidity and vapor density, the relation and application of them was investigated. The results show that the internal micro environment in concrete is different from natural environment, which manifests in forms of cycle, the phase lag and values. In other words, a conclusion can be made that internal micro envrionment in concrete can’t be regard as the natural envrionment. Moreover, the vapor density can be used to describe the humidity change of the natural environment and the characteristic of humidity in concrete.(2) Based on the study of the temperature response in concrete under artificial simulation envrionment, the temperature response model in concrete was established. In addition, the novel method verified by testing was employed to solve the numerical solution of the model. Study results show that the temperature response of internal micro environment in concrete under artificial simulation environment differs from that in natural environment, which is due to the difference of mechanism. In addition, the measured resluts were perfectly fitted to the theoretical curves.(3) Model of the surface factor including temperature and wind speed was deduced, and the numerical simulation method was introduced to discuss the influence of the wind speed on the distribution of the humidity in concrete. Results reveal that the humidity of the external environment can be regarded as the concrete surface humidity when the values of the wind speed and critical drying time are more than a fixed value, such as the wind speed is about3.0m/s, and the critical drying time is about13hours. That may be due to the water transmission of the external environment, concrete surface and internal micro environment reaching equilibrium states.(4) A novel design method for artificial simulation environment test was established, which was based on the response similarity of the concrete micro environment. Through discussing the chang of the internal micro environment in concrete and the boundary conditions, the parameters including the temperature, relative humidity, wetting time, drying time, cycle wind speed and concentration of solution for artificial simulation environment test were selected, which solved the problem of the parameters for the artificial simulation test system. Based on the water transmission model, the influences of the water to cement ratio, initial water saturation and the gradient on the drying-wetting balance time ratio and the water influence depth were investigated. Meantime, the BET adsorption isothermal curve was used to simplify the traditional solving of water characteristic curve. Results show that the drying-wetting balance time ratio and the water influence depth decided by characteristic of concrete and the surroundings can be used as the important indicators to establish the test procedures.(5) Similarity criterion and similarity relation of chloride ion ingress into conrete was discussed, and the test was used to testify the rationality. Models of the diffusion coefficient and convective depth inferred from theoretical analysis were verified by results of the simulated test and field measurement. Meantime, the durability of the typical concrete structures under the chloride environment was also evaluated based on the above method. Results reveal that the relation of the chloride ion content in concrete surface chloride content and altitude or distance from the sea can be decribed by S curve. Generally speaking, the differences of chloride ingress into concrete under the natural and artificial simulation environment mainly manifest as the content, convective depth and the diffusion coefficient, etc. The similarity rate of the chloride ingress into concrete between the natural environment and artificial simulation environment is a fixed value.