Effects of C-S-H gel surface structure on sodium chloride evaporation crystallization in C-S-H gel nanopores with molecular dynamics analysis
Jinbo Yang, Guoqing Zhao, Hang Yin, Yecheng Feng, Peng Zhang
Abstract
The evaporation crystallization of salt solutions in cement-based material pores accelerates durability degradation. It is necessary to investigate the mechanisms and process of evaporation crystallization in the pore channel of C-S-H gels on a nanoscale level. With molecular dynamics simulation, this paper explored the influence of C-S-H gel surface structure on the evaporation crystallization process of NaCl solution based on a new solid–liquid model. NaCl crystallization in the channel space of the C-S-H gel nanopore followed a two-step crystallization mechanism (nucleation and crystallization). The adsorption of sodium and chloride ions on the C-S-H gel surface shows significant differences. The surface of C-S-H gel is electronegative, so the C-S-H gel surface adsorption capacity of cations is stronger than that of anions and the C-S-H gel surface adsorption of sodium ions is more stable. The difference of silica-oxygen tetrahedron density of C-S-H gel surfaces caused the difference of charge characteristic of C-S-H gel surfaces. The C-S-H gel surface structure has an effect on the sodium chloride crystallization position, but has not obvious impact on the two-step evaporation crystallization process. These findings provide a theoretical basis for addressing the nanoscale characteristics of C-S-H gel surface and the macroscale durability of cement-based materials.