Numerical modeling of microstructure development and chloride diffusion coefficient of cement paste with ellipsoidal particles

Abstract

In view of the important role of cement profile in hydration process, pore structure characteristic, porosity and chloride ingression of cement paste, this paper aims to propose a numerical method for predicting the chloride diffusion coefficient of cement paste by considering the particle shape. By introducing periodic boundary conditions and contact function, the three-dimensional fresh cement paste with ellipsoidal particles is firstly constructed. By taking into account the interferences induced by overlapping of hydration layers between adjacent hydrated cement particles and calcium hydroxide precipitation, the vector hydration model is proposed. Each hydrated cement particles is composed of inner and outer hydration layers, unhydrated cement particle and partial calcium hydroxide embedded in the hydration layer. After the validity of hydration model is verified by the experimental data of hydration degree and the content of hydration products, the effects of aspect ratio on hydration degree, pore size distribution and porosity are evaluated. Secondly, based on first-passage theory, the Brownian motion algorithm applicable to voxel model is proposed. In order to improve the simulation efficiency, the first-passage radius and Brownian number are determined. The accurancy of this approach is fully verified by comparing with sufficient experimental data. Finally, resorting to this numerical algorithm, the effects of the aspect ratio and the diffusion coefficients of inner and outer hydration layer on chloride diffusion coefficient are analyzed.