Research And Application On Environment- Time Similarity Model Of Chloride Ion Corrosion In Pre-stressed Structures Under Drying-wetting Cycles

Compared with modern concrete structure, pre-stressed concrete structure has the better performance and higher economic efficiency, material, energy, etc. However, because of erosion of chloride, carbon dioxide and other harmful substances, tendons and ordinary steel rust easily during service. The durability problem has been the general concern engineering field, especially in the high chloride ion coastal environment. Durability problems occur in the internal of pre-stressed concrete structure in advance affected long-term erosion of the sea. Compared with dry environment or wet environment, chloride ion ingress in concrete faster significantly under drying-wetting cycles. Funded by the National Natural Science Fund Project "Research on theory and engineering application of similar marine pre-stressed concrete structure durability(51278230)", the failure mechanism of the pre-stressed concrete structure durability is researched by sampling and artificial climate simulation test in this paper. The main contents are as follows:1.Combining classical similarity theory, analyzing the parameters of the environmental impact of structure in Lianyungang port area to determine main parameters:temperature, chloride ion concentration and ratio of wet and dry. Compared to existing theories, identified a high similarity simulation erosion system of the marine environment, the development of the artificial accelerated test program under drying-wetting cycles.2. Durability test of specimens under drying-wetting cycles is developing. According to the different depth of chloride ion content distribution, comparing and analyzing the experimental data, researching the law of chloride ion transporting in the field and concrete in laboratory. The impact of stress, water-cement ratio and the ratio of wet concrete to concrete durability is obtained.3.According to the law of similarity and Fick’s second law, considering the impact of convection zone depth x’ influence on the chloride ion diffusion, the diffusion coefficient and time coefficient calculation formula under similar field structure with artificial climate simulation environment specimens: the environment-time similar model is established. According to the existing age of the attenuation coefficient model and considering the effect of stress ratio, the existing model is modified with the use of on-site sampling and artificial climate accelerated simulation test data fitting:Tensile stress specimens:nA=(0.7-0.3√n)(2.SW/B-0.6+2·%FA), Stress specimens:nB=(0.9·e-0.15η)(2.5W/B-0.6+1.5·%FA), Specimens: nc=2.5W/B-0.6+2·%FA;4.Based on the environment-time similar model, a method to predict the life of pre-stressed concrete structures is proposed. For example, time coefficient is calculated by analyzing Lianyungang No.60 berth pre-stressed concrete structure and indoor artificial accelerated corrosion test results:λt=7.55. According to the results and the application method:each increase of concrete cover thickness 5mm, life of marine pre-stressed concrete structures extends about 30%; water-cement ratio decreasing by 0.05, life increasing about 10%..