Molecular dynamics study on calcium aluminosilicate hydrate at elevated temperatures: Structure, dynamics and mechanical properties

In order to gain a molecular-level insight on the structure and performance of cement-based materials in high temperature environment, this paper investigates the structure, dynamics and mechanical properties of their main hydration product, calcium aluminosilicate hydrate (C-A-S-H), at elevated temperatures by using reactive molecular dynamics simulation. The results show that rising temperature can destroy the H-bond network of interlayer water molecules in C-A-S-H, leading to pronounced expansion of the interlayer regions. Meanwhile, interlayer water molecules lose its glassy water dynamics and exhibit dramatically high diffusivity with rising temperature. In addition, the calcium atoms show inhomogeneous dynamics at high temperature. At 1500K, the interlayer calcium atoms can escape from their coordination “cages” and diffuse, while the motion of those located in the principal layer are restricted by the Si–O and Al–O bonds throughout the simulation. Furthermore, reactive force field couples the mechanical response and chemical reaction during the uniaxial tensile test for C-A-S-H gel. The de-polymerization and hydrolytic reaction happens frequently in the deformed C-A-S-H gel at high temperature, resulting in degradation of stiffness and strength. On the other hand, the atomic rearrangement at elevated temperature contributes to the re-connection of broken chemical bonds, enhancing ductility of C-A-S-H.