Influence of Pore Size and Fatigue Loading on NaCl Transport Properties in C-S-H Nanopores: A Molecular Dynamics Simulation
Abstract
:1. Introduction
2. Molecular Dynamics Simulation Theory
- (1)
- Establish the micro-structural system needed for a specific project.
- (2)
- Given the initial position and velocity of each atom in the micro-structural system, the appropriate potential function is adopted to calculate the load on each atom. The following two formulas are the speed and position of atom i at time t, which are the core of the numerical solution equation of molecular dynamics simulation. The correctness of the atom’s numerical solution depends on U (potential function).
- (3)
- Based on the obtained position, velocity, and load of the atom at each time, the atom at the upper position is pushed to a lower energy state in a small-time interval, thus generating a new position and velocity.
- (4)
- The positions and velocities of the atoms are updated in the established micro-structural system. The simulation steps mentioned above are repeated until the properties of the system do not change with time, and the structure of the system reaches a stable state. The trajectories of all atoms in the micro-structural system can be obtained.
3. Molecular Dynamics Simulation Details
3.1. Molecular Modeling of NaCl Transportation in C-S-H
3.1.1. Molecular Modeling of C-S-H
3.1.2. Molecular Modeling of NaCl Solution
3.1.3. Molecular Modeling of NaCl in the C-S-H Pore Structure
3.2. Fatigue Loading Application
3.3. Mean Square Displacement (MSD)
4. Results and Discussion
4.1. Influence of Pore Size on NaCl Transport Properties in C-S-H Nanopores
4.2. Influence of Fatigue Loading on NaCl Transport Properties in C-S-H Nanopores
4.3. Discussion
5. Conclusions
- (1)
- Ca2+ and Na+ in the pore wall of C-S-H nanopores can adsorb chloride ions, attracting chloride ions to move towards the pore wall. The attraction effect varies with the pore diameter of C-S-H nanopores. The larger the pore diameter is, the weaker the attractive interaction of the pore walls to chloride ions. The C-S-H pore wall had a strong adsorption effect for cations. The amount of Cl− adsorbed in the solution increases with the increase of the amount of Na+ adsorbed on the pore wall, in which case, chloride ions will be adsorbed to the surface of the pore wall of C-S-H nanopores. In addition, some Cl− will be adsorbed by free Ca2+ in the pore wall of C-S-H nanopores and move to the interior of the C-S-H pore structure.
- (2)
- The C-S-H pore structure is continuously deformed by extrusion under fatigue loading, which leads to the expansion of pore size, thus increasing the chloride diffusion rate. At the same time, more chloride ions will penetrate the concrete cover and diffuse to the surface of reinforcement, which leads to a great increase in the corrosion probability of reinforcement and a decrease in the durability of reinforced concrete structure.
- (3)
- 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 is attributed to the diffusion coefficient of the particles obtained by the experiment being the result of the particles being transported in a large number of pores with different pore sizes.
- (4)
- In this paper, only the transmission process of chloride ions in a single nanopore is considered. The concrete composites contain variety of pore structures with different size. A molecular model with different pore sizes and structures should be established, which can further improve the accuracy of numerical simulation.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Category | Tobermorite 11 Å |
---|---|
Space group | Bm |
Crystal system | Monoclinic |
a/Å | 6.732 |
b/Å | 7.369 |
c/Å | 22.68 |
α/° | 90 |
β/° | 90 |
γ/° | 123.18 |
Diffusion Coefficient (×10−9 m2/s) | Without Fatigue Loading | Under Fatigue Loading | |
---|---|---|---|
Pore Diameter: 1.5 nm | Pore Diameter: 3.0 nm | ||
Chloride ion | 0.287 | 0.896 | 2.502 |
Water molecule | 0.383 | 1.794 | 4.779 |
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Cao, Q.; Xu, Y.; Fang, J.; Song, Y.; Wang, Y.; You, W. Influence of Pore Size and Fatigue Loading on NaCl Transport Properties in C-S-H Nanopores: A Molecular Dynamics Simulation. Materials 2020, 13, 700. https://doi.org/10.3390/ma13030700
Cao Q, Xu Y, Fang J, Song Y, Wang Y, You W. Influence of Pore Size and Fatigue Loading on NaCl Transport Properties in C-S-H Nanopores: A Molecular Dynamics Simulation. Materials. 2020; 13(3):700. https://doi.org/10.3390/ma13030700
Chicago/Turabian StyleCao, Qingyu, Yidong Xu, Jianke Fang, Yufeng Song, Yao Wang, and Weiguo You. 2020. "Influence of Pore Size and Fatigue Loading on NaCl Transport Properties in C-S-H Nanopores: A Molecular Dynamics Simulation" Materials 13, no. 3: 700. https://doi.org/10.3390/ma13030700