关键词: 水化硅酸钙;分子动力学;扩散系数;径向分布函数

Abstract: Calcium silicate hydrate (C-S-H) gel is the most basic binder phase in cement hydration products.The transport of water and ions in gel pores fundamentally determines the service life of the cement concrete materials.Molecular dynamics method is used to study the transport process of water molecules, chloride ions and sodium ions in hydrated calcium silicate gel pores of 1 nm, 2 nm, 3 nm and 4 nm.Based on the analysis of radial distribution function and mean square displacement, it is found that the molecular structure and dynamics characteristics of the ions and water are different from those of the capillary water.The water molecules order arrangement, ions adsorption at the interface and diffusion rate decreases sharply.These characteristics of the structure and dynamics of molecules are because that non bridging oxygen at the silicate chains located at the surface of C-S-H can form stable hydrogen bonds with water molecules, and sodium ions can form Na-O chemical bonds.Meanwhile, calcium ions in the surface can also form CaCl2 clusters with chloride ions.In addition, with the diameter increasing, the diffusion coefficient of ions and water molecules gradually increases from 0.15×10-9 m2/s, 0.7×10-9 m2/s to 1.3×10-9 m2/s, 3×10-9 m2/s, which is very close to the value of capillary water measured by experiment.On the nano scale, pore size constraint and interfacial chemical bonding are the key factors in determining ions and water molecules transport.

Key words: calcium silicate hydrate;molecular dynamics;diffusion coefficient;radial distribution function