Y. Tu, L. Yuan, D. Liu, J. Cao, Y. Ding, O. Das, M. Försth, G. Sas and L. Elfgren, “Molecular dynamics simulations of chloride and sulfate ion transport in C-S-H gel and γ-FeOOH nanopores.” Journal of Advanced Concrete Technology, 720- 731, December 2022. 1 Supplementary materials 1. Penetration depth-time curves To quantitatively characterize solution transport in the nanopores, the trajectories of water and ions at the front were recorded. Fig. S1 shows that the penetration of water into the pores slows gradually over time, in accordance with the L-W equation (Washburn 1921). In systems containing an NaCl solution, penetration depth decreases in the order water>Na + ≈Cl - ; the single Na + and Cl - at the front move more slowly than the water. Additionally, in systems with Na2SO4 solutions, penetration depth decreases in the order water>Na + >SO4 2- . This is because Na + and SO4 2- form ion clusters at the front and move forward together but there are also unclustered Na + and SO4 2- at the front and the hydration structure of SO4 2- is larger than that of Na + , which explains its lower mobility. In the C-S-H system featuring the mixed solution, penetration depth decreases in the order water>Na + >SO4 2- >Cl - . Due to randomness, there are no Cl - at the pore entrance at the end of the initial relaxation period, leading to a substantial lag in Cl - transport at the start. However, Cl - gradually catch up with Na + and SO4 2- , as shown by the continuously narrowing gap in penetration depth. For the γ-FeOOH system with the mixed solution, the penetration depth decreases in the order water>Na + >SO4 2- >Cl - from 0 to 1200 ps, while from 1200 to 1500 ps it decreases in the order water>Na + >Cl - >SO4 2- . It can be seen that the transport rates of all three simulated solutions are lower in γ-FeOOH nanopores than in C-S-H gel nanopores. For example, the water penetration depths in the C-S-H+NaCl and γ-FeOOH+NaCl cases at 1500 ps are 88 Å and 78 Å, respectively, reflecting the differing hydrophilicities of the two substrate surfaces. (a) C-S-H+NaCl (b) γ-FeOOH+NaCl (c) C-S-H+Na2SO4 (d) γ-FeOOH+Na2SO4