Integrating electric double layer time-varying and dual interface slip for predicting migration behavior of moisture and ions

Abstract

Migration of moisture and chloride ions in calcium-silicate-hydrates (C-S-H) nanopores is important factor for controlling the durability of concrete and affecting the physical and chemical properties of cement-based binder. Quantitative analysis of experimental results indicates that the pore in C-S-H is mainly distributed on the nanometer scale. Due to the prominent interfacial effects at the nanoscale, moisture and ions in different regions within nanochannels exhibit distinct molecular structures and dynamic properties. Therefore, the wetting behavior of the synthesized C-S-H surface and its influence on microfluid dynamics analysis and boundary condition definition were systematically analyzed based on the contact angle experiment. Statistical thermodynamics were introduced to describe the time-varying characteristics of the electric double layer (EDL). With the interaction as the theoretical framework and interaction energy as an important parameter, the equilibrium behavior of interacting particles was studied to describe the stability of EDL system. The flow control equation and boundary conditions were modified considering the action of EDL. The transport model of moisture and chloride ions under the combined influence of electric double layer and dual interface slip was proposed. The results show that the existence of EDL impedes the movement of the fluid, while the dual slippage of water film and time-varying of EDL reduce the resistance. Quantitative analysis indicates the contribution ratios of water film slip and EDL time-varying can reach 85% and 29%, respectively. In addition, water film slip has a greater influence on water migration and EDL time-varying has a greater influence on ions. This research can provide new insights into the transport mechanism of water and chloride ions at micro-nanoscale.