Stress relaxation properties of calcium silicate hydrate: a molecular dynamics study

The time-dependent viscoelastic response of cement-based materials to applied deformation is far from fully understood at the atomic level. Calcium silicate hydrate (C-S-H), the main hydration product of Portland cement, is responsible for the viscoelastic mechanism of cement-based materials. In this study, a molecular model of C-S-H was developed to explain the stress relaxation characteristics of C-S-H at different initial deformation states, Ca/Si ratios, temperatures, and water contents, which cannot be accessed experimentally. The stress relaxation of C-S-H occurs regardless of whether it is subjected to initial shear, tensile, or compressive deformation, and shows a heterogeneous characteristic. Water plays a crucial role in the stress relaxation process. A large Ca/Si ratio and high temperature reduce the cohesion between the calcium-silicate layer and the interlayer region, and the viscosity of the interlayer region, thereby accelerating the stress relaxation of C-S-H. The effect of the hydrogen bond network and the morphology of C-S-H on the evolution of the stress relaxation characteristics of C-S-H at different water contents was elucidated by nonaffine mean squared displacement. Our results shed light on the stress relaxation characteristics of C-S-H from a microscopic perspective, bridging the gap between the microscopic phenomena and the underlying atomic-level mechanisms.