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

Abstract

Interactions between Cl^-, SO₄^2- 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. SO₄^2- 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 H_o (hydroxyl hydrogen atoms) -Cl, H_o-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.