Molecular Dynamics Study of Water and Ions Transported during the Nanopore Calcium Silicate Phase: Case Study of Jennite

Durability is an important property that determines the long-term behavior of cement-based materials. Water and ions are transported in nanopores of calcium-silicate-hydrate (C-S-H) gels, the main element in cement-based material, which significantly influences the durability of cement. Because of its structural similarity, jennite, an important mineral analog of C-S-H gel, is first taken to investigate the transport behavior at a molecular level. In this paper, structural and dynamical properties of the water/ions and the jennite interface are studied by the molecular dynamics (MD) simulation method. On the (001) surface of jennite, water molecules diffusing in the channel between silicate chains demonstrate the following structural water features: large density, good orientation preference, ordered interfacial organization, and low diffusion rate. The channel water molecules have more H-bonds connected with the neighboring water molecules and solid surface. As the distance from the channel increases, the structural and dynamical behavior of water molecules varies and gradually translates into bulk water properties at 10-15 angstrom from the liquid-solid interface. With respect to the interaction between jennite and the ions, the surface demonstrates Cl- repulsion and Na+ adsorption. With increased ion concentration, the jennite adsorption capability for Cl- is enhanced because Na+ and Cl- aggregate to form a cluster in the interfacial region. The simulation results, matching well with the Cl35 Nuclear Magnetic Resonance (NMR) studies and isotherm adsorption tests, give a molecular-scale interpretation of experimental studies