Diffusion Model Of Sulfate Ions In Concrete Based On Evolution Of Erosion-induced Damage

Sulfate attack is one of the important reasons for the degradation of durability in coastwiseconcrete structures. The evolution of micro-cracks results in the deterioration of mechanicalproperties of concrete materials，and it will affect the diffusion of sulfate ions in concretesignificantly. The service life of concrete structures is directly related to the diffusion properties ofsulfate ions, such as diffusion depth and concentration of sulfate ions. Therefore, the study ofdiffusion model of sulfate ions in concrete based on the evolution of erosion-induced damage canprovide the important theoretical guidance and estimation of service life for the engineeringapplication of concrete structures.The mechanism of erosion and influential factors of sulfate attack are reviewed with extensivesurvey of literature. Moreover, the progresses in the research on diffusion model of sulfate ions inconcrete are introduced. According to Fick’s second law and the continued hydration of concrete, anew diffusion model of sulfate ions in concrete based on evolution of erosion-induced damage willbe proposed. Evolution of erosion-induced damage treated as increase of porosity is substitutedinto diffusion coefficient of model. The damage function which characterizes evolution of damageis not only an important component of this diffusion model, but also an innovation thatdistinguishes this model from others. The damage function related to erosion time andconcentration of sulfate ions can be obtained by ultrasonic testing. The numerical method isadopted to solve the nonlinear parabolic partial differential equation and the effect of theconcentration of outside solution, the initial porosity of materials and damage evolution on sulfateionic diffusion is analyzed by this model. The numerical results show that the higher theconcentration of aggressive solution is, the more remarkably and quickly the ions diffuse inconcrete; the greater the initial porosity is, the more quickly the ions do as well; because ofexistence of damage evolution, the ionic diffusion will be accelerated with time increasing.For comparing with the numerical results of diffusion model, the experimental study ofdiffusion of sulfate ions is carried out. By drill sampling and EDTA complexometric titration, thetemporal and spatial distribution of sulfate ions in specimen is measured quantitatively.Simultaneously, the numerical results of diffusion model are compared with the experimental data.It shows the numerical results agree well with the experimental data. Because of the size of the original ultrasonic probes, the small cylindrical probes are designed to measure the wave velocityat different depths of diffusion. It provides a testing method effectively to study the coupling effectof ionic diffusion and evolution of erosion-induced damage.Finally the main conclusions and innovations are shown and some suggestions are presentedfor future research as well.