Boundary Element Model Of Chloride Diffusion In Three-Phase-Structure Concretes And Its Durability Analysis

The traditional uniform concrete model cannot accurately reflect the chloride ion diffusion and accumulation behavior in concrete. In this dissertation, concrete is seen as a three-phase material, which includes mortar, aggregates and interfacial transition zone (ITZ). Then, a three-phase structure concrete model is built based on the initial time marching scheme (ITMS) of boundary element method(BEM), to analyze the diffusion and distributipn of chloride ion in concrete under the condition of aggregate randomly distributed. Next, combining with the limit state equation of durability failure in marine concrete structure, here conducts the reliability analysis of durability of concrete structure, which is exposed in chloride environment.The main academic work and conclusions are as follow:(1) The concrete is seen as a three-phase material. Based on the single connection domain BEM of chloride diffusion, here divide mortar and ITZ into two diffusion regions, and connect the aggregate boundary with ITZ boundary by virtual boundaries, the same as the ITZ boundary with concrete boundary, so each region is turned into a multiple connection domains, when considering the condition of the common boundary, a boundary integration equation of the three-phase structure concrete can be deduced. Analysis shows that it only needs sparse discrete in space and time domains to ensure accuracy and has a high computational efficiency.(2) Based on the proposed three-phase model, here simulates the chloride ions diffusion in concrete modeling with a single aggregate contained, round aggregates orderly placed and polygonal aggregates stochastically placed respectively, to investigate the effect of aggregate’s characteristics, such as size, content, gradation, arrangement etc., and the diffusion coefficient of ITZ on the distribution of chloride concentration in concrete. The results show that, effect of aggregate content is reflected in two aspects, owing to difference of volume fractions, to the chloride ion diffusion, when the aggregate content ranges from 20% to 50% and the aggregates are distributed evenly, the blocking effect of aggregate is stronger than the acceleration of ITZ, chloride concentration decreased with increasing aggregate content, however, the influence of changing of the aggregate shape, gradation and arrangement on the average chloride concentration in concrete is not so obvious.(3) With the proposed three-phase model, a limit state equation of concrete structure durability failure in chloride environment is built, to analyze the durability of concrete structures base on the aggregate randomly distribution in spatial, and determine the reliability index of the durability of concrete structures. The research shows that, when the aggregate content ranges from 20% to 50% and the aggregates are distributed evenly, improving aggregate content within a certain range can help to improve the reliability index of the structural durability, but improving the diffusion coefficient of ITZ will produce the opposite effect, and the impact of changing aggregate gradation is not obvious.