Shape effect of cement particles on the ionic diffusivity of hardened cement paste—a three-dimensional numerical investigation

•Shape effect of cement particles on the ionic diffusivity of pastes is presented.•Sphericity is an important factor affecting the diffusivity of HCP.•Hydration age and w/c ratio can affect shape effects on diffusivity.•The intrinsic reason is microstructure, especially pore structure. A three-dimensional numerical investigation is presented to study the shape effect of cement particles on the ionic diffusivity of hardened cement paste (HCP), whose microstructure is generated based on the random packing models of spherical and polyhedral particles. The microstructure of HCP composed of four phases is first generated and then converted into a voxel-presented one. Based on the digitized microstructure, the diffusivity of HCP can be obtained by a lattice modelling. The reliability of simulations is validated by comparing to experimental data and the shape effect of cement particles on the diffusivity of HCP is discussed. The results indicate that the shape of cement particles significantly affects the ionic diffusivity of HCP due to its effect on the hydration degree: the cement particles with smaller sphericity contribute to the hydration of HCP, which reduces the ionic diffusivity of HCP. This effect decreases as the hydration age elapses and increases with the increasing water-cement ratio. The intrinsic reason causing this effect is illustrated from the microstructural view of HCP: the shape effect has an influence on the volume fractions of three diffusive phases and pore structures.