and Fang J. (2019). "Studying the mix design and investigating the photocatalytic performance of pervious concrete containing TiO2-soaked recycled aggregates."
The transport properties of chloride ions in cement-based materials are one of the major deterioration mechanisms for reinforced concrete (RC) structures. This paper investigates the influence of pore size and fatigue loading on the transport properties of NaCl in C-S-H nanopores using molecular dynamics (MD) simulations. Molecular models of C-S-H, NaCl solution, and C-S-H nanopores with different pore diameters are established on a microscopic scale. The distribution of the chloride ion diffusion rate and the diffusion coefficient of each particle are obtained by statistically calculating the variation of atomic displacement with time. The results indicate that the chloride ion diffusion rate perpendicular to C-S-H nanopores under fatigue loading is 4 times faster than that without fatigue loading. Moreover, the diffusion coefficient of water molecules and chloride ions in C-S-H nanopores increases under fatigue loading compared with those without fatigue loading. The diffusion coefficient of water molecules in C-S-H nanopores with a pore size of 3 nm obtained from the MD simulation is 1.794 × 10−9 m2/s, which is slightly lower than that obtained from the experiment.
This paper describes the corrosion process of reinforcing steel under both chloride attack and mechanical loading. Molecular dynamics simulation is adopted to investigate the evolution process of passive film and oxidation process of reinforcement. The mean square displacement and self-diffusion coefficient of O2 under different conditions are also obtained based on molecular dynamics simulation. It is shown that the present of chlorides can increase the energy of Fe atoms on the surface of Fe3O4 substrate, leading Fe atoms to separate from Fe3O4 easily and to get more chance to react with oxygen atoms. The interaction of chloride attack and mechanical loading can aggravate the damage of passive film on the surface of reinforcement and result in an increase of oxidation depth of Fe matrix. The coupled effects of chloride and static loading can accelerate the diffusion of O2 to the iron matrix, thus increasing the oxidation reaction between the iron matrix and O2.
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