“…A microstructure of cementitious materials inherently exhibits a heterogeneous composition, which can result in the non-Gaussian diffusion of gases. To effectively describe the diffusion in heterogeneous material, the concept of fluctuating diffusivity (FD) [18,19,20,21,22,23,24] has been demonstrated to be useful, as evidenced by the studies for the glass forming liquid [25], colloidal suspensions [26,27], and biological systems [28,29]. The diffusion of a free molecule with fluctuating diffusivity is described by the equation…”