Gas diffusion in cement pastes: An analysis using a fluctuating diffusivity model

This study proposes applying the concept of fluctuating diffusivity (FD) to the diffusion of gas molecules in cementitious materials, mainly through a two-state fluctuating diffusivity (2SFD) model. The 2SFD model was utilized to investigate oxygen diffusion in cement pastes. This analysis provides a reasonable description of the oxygen diffusion coefficient in cement pastes and suggests the presence of non-Gaussian diffusion, which is attributed to the heterogeneous microstructure. The presence of non-Gaussianity in the probability density of the displacement of the molecule, characterized by heavier tails than those of the Gaussian distribution, may significantly impact the durability of concrete structures.