Molecular Dynamics Study on Mechanical Properties of Calcium–Silicate–Hydrate Considering Model and Parameter Effects

The micro and nano scale composition in concrete is one of the essential topics at the moment. At nanoscale, calcium–silicate–hydrate (C–S–H) gel is the main material phase that determines the mechanical properties in cement hydration. In the past decade, a lot of research work has been developed based on the molecular structure of C–S–H gels. Since its structure is difficult to be uniquely determined by experimental methods, the diversity of models and parameters may lead to differences in calculation results when characterizing C–S–H properties. Therefore, this paper mainly focuses on the comparative study of the common model structures and force field parameters in C–S–H molecular dynamics simulations, and specifically discusses the effects of mechanical properties with Hamid and Merlino tobermorite structures, silica-oxygen tetrahedral distribution, OH groups, water models and force fields. The research results show that the differences in models and parameters have indistinctive influence on the value of the elastic modulus, and the anisotropy of the molecular structure is generally consistent. However, the two tobermorite structures, the uniform distribution of silica groups, and the setting of the force field have obvious differences in plastic deformation and fracture behaviors. When studying large deformation and creep, it is necessary to choose the model structure and parameters carefully. The elastic modulus and mean square displacement calculated based on different water models have consistent regularity. The choice of water model has a significant impact on viscosity and interfacial adhesion, which needs to be considered when studying water diffusivity and drying shrinkage. The research results provide detailed guidance and suggestions for the model and parameter selection of further studies in C–S–H molecular dynamics simulation.