A hybrid analytical-numerical algorithm based general modeling framework of molecular diffusivity in cement paste

Diffusion phenomena such as the ingress of various deleterious ions are of crucial importance to the service life of reinforced concrete. A physical parameter, i.e., the molecular diffusion coefficient or diffusivity is often used to define the diffusion rate. To date, the determination of molecular diffusivity remains a challenging issue, though numbers of laboratory tests and modeling methods have been developed. This paper is to present a general modeling framework of molecular diffusivity in cement paste. The necessary inputs come from the usual tests of X-ray computed tomography and mercury intrusion porosimetry, while a two-level hybrid analytical-numerical algorithm is proposed. At the voxel level, a general expression of modified Archie's equation is derived upon a combination of tortuosity model and fractal theory. At the cement paste level, a finite element method is adopted for the sake of homogenization. It is shown that the general modeling framework can be a good alternative to predict the molecular diffusivity in cement paste from the knowledge of structural feature as determined through experiments.