The 4th Asian Concrete Federation Symposium on Emerging Technologies for Structural Longevity (ACF2023- ETSL)

271 / 2022-09-19 15:30:05

Application of molecular dynamics simulation in green building materials

Al incorporated cementitious materials,C-A-S-H,Molecular dynamics,Mechanical properties,Transport behavior

To achieve low-energy consumption and environmentally friendly green design of building materials, the aluminum-rich mineral admixtures (fly ash, mineral powder, metakaolin, and etc.) were introduced into cementitious materials, resulting in the formation of calcium aluminosilicate hydrate (C-A-S-H) gel. In this paper, the molecular dynamics (MD) simulation method was utilized to investigate the nanostructure, mechanical and transport properties of C-A-S-H gel. The results show that at molecular scale, Al[4] in C-A-S-H structure can bridge the defective silicate chains to form longer aluminosilicate chains. As compared with bridging silicate tetrahedra, the presence of bridging aluminate species shows the same influence on the mean chain length of aluminosilicate chains but increase the basal spacing of C-A-S-H gel. Compared with C-S-H, the water molecules in the vicinity of the C-A-S-H interface exhibit characteristics: Larger bulk density and dipole moment, water molecules are arranged in order, and the inclination angle is consistent. The surface of C-A-S-H is fixed with more Na⁺ and Cl^-, and the reasons for adsorption of anion and cation are different (Fig. 1). The transport behavior of water and ions in C-S-H/C-A-S-H nanopore was explored and the microscopic mechanism was revealed. The unsaturated transport curve of NaCl solution in C-S-H/C-A-S-H nanopore meets the classical capillary adsorption theory Lucas-Washburn equation. The migration of water molecules and ions in the C-A-S-H gel pores is slower than that of C-S-H. The introduction of aluminum in C-S-H resists the intrusion of water and ions (Fig. 2). Furthermore, Al incorporation shows little effect on the mechanical properties along x and z directions while increases its mechanical properties in y direction (Fig. 3). The research results of this paper can provide theoretical basis for the design and preparation of sustainable and environmentally friendly cement-based materials.