Numerical Simulation Of Loads, And Sulfate Attack Coupling Sulfate Ion Diffusion Reaction In Concrete

The durability damage of concrete not only shorten the service lifetime of concrte structures, but also reduce the safety and reliability of engineering structures. Sulfate attack is one of the important environmental factors that causes the damage of concrete durability. It is a matter of great significance for improving the safety on the design of concrete structures and predicting the service lifetime of concrete structures to study the durability of concrete structure under environmental sulfate attack and mechanical loadings. The main contexts in the present study include as follows:Firstly, the actuality of concrete structure durability and the damage mechanism of concrete under sulfate attack are introduced. Secondly, based on geometrical method, a three dimensional geometry model for tortuosity of hardened cement pastes have been established, and making use of the phenomenological method, the tortuosity in concrete with the stress actions may be expressed; circularity of concrete aggregate is an important impact parameters of tortuosity model, Matlab image processing technology and eight chain code method is presented, the characterization method of concrete aggregate particles shape have been established; and the model of the diffusion coefficient of sulfate ion considering the effects of stress action on the diffusivity is obtained and simplified it. Finally, based on Fick law and chemical reaction kinetics, a 1-D nonlinear and non-steady equation for the diffusion reaction behaviors of sulfate ion in concrete is proposed under the couplings of environmental and mechanical loadings, and the numerical solutions are obtained by the finite difference method. Besides, the diffusion reaction behaviors of sulfate ion in concrete are analyzed by numerical simulations under environmental sulfate attack and mechanical loadings.The results show that, concentration distribution and concentration expended of the sulfate ion present ladder in concrete. In the initial stage, the sulfate ion concentration increased rapidly in concrete, with diffusion time increasing, the concentration distribution of sulfate in concrete trend to be stable. The mechanical loadings significantly improve ion transmission performance in concrete under environmental sulfate attack and mechanical loadings. Thus, the concentration distribution of sulfate ion in concrete under the mechanical loadings is greater than the one in concrete without loadings, and the transmission rate of sulfate ions in concrete with the increase of stress ratio increased.