Numerical Simulation Of Microstructure Development And Transport Properties Of Multiple Cementitious Materials

With the implement of the construction of "One Belt, One Road" and "Development of Sea Power", a large number of infrastructure constructions have been promoted, such as bridges, harbors and high-speed trains, contributing to the increasing consumption of concrete materials. The durability of concrete structure materials has become a tremendous challenge in severe environments, for example ocean and salt lakes. With the development of technology of modern concrete materials, various mineral admixtures have large-scale applied in modern cementitious materials, which leads to complex components, low activities and large variation and then contributes to the complicated micro structure, unpredicted strength and increasingly difficult problem of durability. The development of computer technology has become a powerful tool in cementitious materials.In this paper, based on the modeling mechanism of cement hydration model of digital image technology, multiple cementitious materials hydration model has been built up to simulate cement hydration process and microstructure development. The algorithm of solving chloride diffusivity has been developed. Based on this and conbined with multiscale theory and finite difference method, chloride diffusivity in multiple cementitious materials has been predicted with the microstructure development. Furthermore, chloride transport properties in sound concrete have been investigated. Considering the effect of crack width on chloride diffusivity in crack(s), the mathematical formula of chloride diffusivity in crack has been present. Conbined with finite difference method, the effect of different crack characteristics on transport properties in concrete is investigated. Main innovative results of thesis are as follows:(1) Buiding up multiple cementitious materials hydration model.Based on the modeling mechanism of initial CEMHYD3D model-three main process of "construction of initial microstructure-phase segregation-hydration rules", and the process of "dissolution-diffusion-nucleation/precipitation" controlled by cellular automaton rules, the multiple cementitious materials model is built up to simulate hydration process and microstructure development of binary, ternary and multiple cementitious, acquiring the distribution of cement particles, hydration products and pore and the interaction between mineral adimixtures and cement and mineral admixtures. The algorithm of charactering pore structure is developed and the process of pore structure is monitered continuously.(2) Studying transport properties in sound concrete based on microstructure developmentBased on the multiscale theory and representative volume element, the structures of cementitious materials at different scales have been built up respectively. Combined with Fick's first law and finite difference method, "Lattice Transport Method" is developed to predict chloride diffusivity. Based on this method and multiple cementitious materials hydration model, the method of the diffusivity of cementitious materials at different scales is present. At the same time, conbined with Fick's second law and the law of mass conversation, chloride transport behavior in sound concrete is investigated. Then considering the critical chloride concentration of rebar corrosion, the method of service life assessment is present.(3) Studying transport properties in cracked concrete based on crack characteristicsThe transport model in cracked concrete is developed based on the mathematic model of the chloride diffusivity in different cracks of width, conbined with the experimental data. The influence of crack characteristics on transpot properties in concrete, including open and closed crack(s), width, depth, quantity and orientation, is investgated in detail. At the same time, chloride concentration can be obtained visually.