Influence of Pore Size and Fatigue Loading on NaCl Transport Properties in C-S-H Nanopores: A Molecular Dynamics Simulation.

Qingyu Cao,Yao Wang,Weiguo You,Yidong Xu,Jianke Fang,Yufeng Song

doi:10.3390/ma13030700

Abstract

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.

Highlights

The deterioration of reinforced concrete structures in coastal areas is mainly caused by chloride ions [1,2]
The number of chloride ions transported to the pore wall decreases with increasing pore size, which can be attributed to the interaction potential of the pore wall on chloride ions decreasing with increasing pore size [17]
C-S-H nanopores under fatigue loading, Cl− appears in the range of 20–50 Å, which indicates that the fatigue load forces a large amount of Cl− into the pore wall

Summary

Introduction

The deterioration of reinforced concrete structures in coastal areas is mainly caused by chloride ions [1,2]. Considerable research has been carried out on corrosion properties in structural concrete on a macro level [3,4,5]. Nemecek [6] considered the concentration change of chloride ions under diffusion convection and simulated the transport of chloride ions in reinforced concrete models with FEM simulation, which is based on Fick’s first law. Li [7] introduced a multiscale approach of combining both mesoscopic models, including full-graded aggregate and equivalent macroscopic models. Carsana [8] investigated the effects of chlorides in raw materials, such as recycled aggregate from salt-contaminated concrete structures, on the durability of concrete. The tested durability-related properties included capillary water absorption, chlorides, and carbonation penetration.

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