Molecular Dynamics Simulations of Chloride and Sulfate Ion Transport in C-S-H gel and γ-FeOOH Nanopores

Interactions between Cl-, SO42- and cementitious materials, reinforcement passive films influence the durability of reinforced concrete structures. Transport of three solutions (NaCl, Na2SO4, mixed) in calcium silicate hydrate (C-S-H) gel, γ-FeOOH nanopores was investigated using molecular dynamics. Solution transport in γ-FeOOH nanopores is slower than in C-S-H gel nanopores because of the lesser hydrophilicity of γ-FeOOH surface. SO42- can form ion clusters to hinder the solution transport and atomic motion, and the ion clusters appear in the solution more frequently than at the interface. Temporary adsorption of Cl-, SO4
2- on substrate surfaces occurs during transport because of Ca-Cl, Ca-SO4 ionic bonds on the C-S-H surface and Ho (hydroxyl hydrogen atoms) -Cl, Ho-SO4 hydrogen bonds on the γ-FeOOH surface, and these bonds are influenced by the local structure. Two substrates interact with water, Cl-, SO4
2- via distinct microscopic mechanisms.