Molecular dynamics study on sodium chloride solution transport through the Calcium-Silicate-Hydrate nanocone channel

As the main hydration product of concrete materials, calcium silicate hydrate (CSH) determines the service life of the concrete. In this work, molecular dynamics was employed to investigate the transport of water and ions in the CSH nanocone pores which cause the deterioration of the internal components of the concrete. The simulation results show that the advanced frontier of NaCl solution flow inside the CSH capillary shows a concave meniscus shape, which reflects the hydrophilic properties of the CSH substrate. The ions migration rate is slower than water molecular in the CSH nanocone channel. The local structure of ions and the distributions of intrinsic electrostatic potential along the nanocone channel were analyzed to elucidate the migration discrepancy. The adsorption of ions on the CSH substrate, the formation of ions clusters in the CSH nanocone, and the tip blocking of CSH nanocone on ions migration are responsible for the transport discrepancy between water and ions. Besides, the effect of inclination angles of CSH substrate on the transport behavior was also investigated. With increasing inclination angles, the tip blocking becomes stronger, and the penetration transport discrepancy between water and ions becomes starker and more manifest. This work provides fundamental insight into the transport behavior of liquid in the gel pores of a cement-based material.