The coupled effect of moisture diffusion chloride penetration and freezing-thawing on concrete durability

In this thesis, both theoretical and experimental studies were conducted on some of the processes related to concrete durability. Those processes include moisture diffusion, chloride penetration, freezing-thawing and their coupled effects.; The first part of the study includes theoretical modeling of the coupled effect of moisture diffusion and drying shrinkage and modeling of chloride penetration in partially saturated concrete. This part encompasses the formulation of the governing equations and boundary conditions, identification and modeling of the material parameters and the numerical solution. The governing equations of moisture diffusion and chloride penetration in concrete were characterized by the nonlinear diffusion equation derived based on Ficks' laws. The material parameters involved in the governing equations and the drying shrinkage of concrete were modeled based on a multiscale method. In the multiscale method, different theoretical models are used at different scale levels. Diffusion mechanisms and shrinkage mechanisms are considered at the nanoscale; a composite mechanics method (generalized self-consistent method, in particular) is used at the microscale and mesoscale; and continuum approach is applied at the macroscale. The numerical models were solved by the Alternating-Direction Implicit (ADI) finite difference method. Several numerical examples were solved by the proposed models and the results obtained predicted well the basic trends and the effects of concrete material parameters. The models can be used in the durability studies of concrete structures to predict concrete deterioration and the onset of steel corrosion and thus the service life and the time for rehabilitation.; The second part of this study includes experiments on the coupled effect of freezing-thawing and chloride penetration, effect of concrete material parameters on chloride penetration, the coupling effect of moisture diffusion and chloride penetration and the effect of shrinkage-induced cracking on chloride penetration. The experimental study presented the effect of water-cement ratio and aggregate volume fraction on chloride penetration, the two-way coupling between moisture diffusion and chloride penetration and the effect of the damage induced by drying shrinkage and freezing-thawing on chloride penetration. The experimental results obtained in this study can be used to validate and demonstrate the accuracy of the numerical models developed in this study and the future studies.