Two-Scale Modeling of the Capillary Network in Hydrated Cement Paste

Objective: Studies on pore structure are essential to better understand the transport properties and durability of cement based materials. In this study, a two-scale modeling framework is proposed to simulate the capillary pore network in hydrated cement paste.
Methods: Capillary pores are divided into small capillary pores (SCPs) and large capillary pores (LCPs). It is assumed that all SCPs are embedded in the outer calcium silicate hydrates (C-S-H) layer, which is the mixture of low density (LD) C-S-H and SCPs at sub-micro-scale. The porosity of outer C-S-H layers is found to be a function of the water-to-cement ratio ( w/c ) and the degree of hydration. Using this porosity to define the status, the outer C-S-H layer is simulated as a two-phase mixture based on a sub-micro-scale status-oriented model. Using the degree of hydration to define the status of a cement paste, cement paste is simulated as a mixture of unhydrated cement cores, inner hydration products, outer C-S-H layers, micro-sized crystal hydrates particles and large capillary pores, based on a micro-scale status-oriented model.
Results: The two computer models developed for pore structure simulations of cement paste, at different scales, are verified by nitrogen adsorption and microscopic image processing, respectively.