Representative elementary volumes for 3D modeling of mass transport in cementitious materials

Representative elementary volumes (REV) are of major importance for modeling the transport properties of multi-scale porous materials. REVs can be used to schematize heterogeneous microstructures and form the basis of a numerical analysis. In this paper, the most appropriate REV size for numerical modeling for mass transport in hydrating cement paste is investigated. Numerous series (264) of virtual three-dimensional (3D) microstructures with different porosities and pore morphologies were generated using Hymostruc, a numerical simulation model for cement hydration and microstructure development. The influence of the initial particle size distribution, hydration evolution, numerical resolution and type of transport boundary conditions (periodic versus non-periodic) was investigated. The effective diffusivity was obtained by using a 3D finite difference scheme. The connectivity, dead-end porosity, tortuosity and constrictivity of the capillary pore network was evaluated. Based on a statistical chi-square analysis, it was concluded that the REV size largely depends on the complexity of the pore morphology, which in its turn, primarily depends on the degree of cement hydration, i.e. the porosity of the simulated microstructure, the employed numerical resolution as well as on the initial particle size distribution of the unhydrated cement grains. Furthermore, the results proved that employing periodic boundary conditions can effectively decrease the variability of the calculated effective properties and, thus, lower the size of an REV.