Static and Dynamic Interfacial Interactions of Geopolymer-aggregate Considering Anisotropic Mineral Surfaces: A Molecular Dynamics Study

Geopolymer, as a low-carbon environmental protection and valuable inorganic cementitious material, its interfacial interaction with aggregates with different surface structures directly affects the mechanical properties and durability of geopolymer concrete. In this study, considering the anisotropy of aggregate minerals surfaces, molecular dynamics (MD) simulation was used to investigate the interfacial interaction between geopolymcr and aggregate. Simulating at the atomic and molecular level, the static interfacial interaction between N-A-S-H, C-A-S-H and SiO2, CaCO3was simulated. Then the dynamic mechanical behavior of different interfacial interaction systems was carried out by direct tensile simulation. The simulation results show that the surface energy and wettability of CaCO3are stronger than that of SiO2, and the interfacial interaction potential and tensile stress of CaCO3with C-A-S-H and N-A-S-H are stronger. However, the anisotropy of CaCO3crystal surface is significant, and its performances are more unstable than that of SiO2. The interaction energy between geopolymcr and aggregate minerals is mainly provided by electrostatic energy. And in the interaction zone, water molecules gathered and hydrogen bonding is obvious because of the electrostatic interaction and wettability of mineral surfaces. In addition, water molecules coordinate with Ca2+and Na+to form hydrated ions, which is conducive to ion migration, precipitation, nucleation, and growth on the mineral surface, and enhances the interfacial stcric hindrance effect. In direct tension simulation, the failure mechanism of geopolymer-aggregate interface includes two stages. The first stage is caused by electrostatic interaction being overcome (0 nm<d<0.15 nm), and the second is caused by hydrogen bond fracture at the interface (0. 15 nm≤d ≤ 0.3 nm). © 2022 Xi'an Highway University. All rights reserved.