Two-scale modeling of the capillary network in hydrated cement paste

• Capillary pore network in hydrated cement paste is modeled at two different scales.
• Two status-oriented computer models are developed for the simulation works.
• The simulation methods are validated by appropriate experimental results.

ObjectiveStudies 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.MethodsCapillary 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.ResultsThe two computer models developed for pore structure simulations of cement paste, at different scales, are verified by nitrogen adsorption and microscopic image processing, respectively.