Effect of capillary connectivity and crack density on the diffusivity of cementitious materials

Effective diffusivity of a cementitious material mainly depends on the connectivity of the capillary system and the material integrity. A number of influencing factors could lead to variation in capillary connectivity by growth of porosity and loss of material integrity mainly by cracking, and thus it is difficult to estimate the material diffusivity in general. In this paper, a mixed effective medium theory (MEMT) is developed so as to consider the influence of arbitrary capillary connectivity and crack density. The model takes advantage of the Mori-Tanaka (MT) method, interaction direct derivative (IDD) and the self-consistent (SC) method. Using a three-level homogenization scheme, the proposed model is validated against a series of experimental measurements on cement pastes. Furthermore, the MEMT model is adopted in the numerical simulation of the external sulfate attack (ESA) on cement paste, and the influence of crack density on the effective diffusivity is studied. The obtained results on the mineralogical degradation during the ESA agree very well with the reported experiments.