Interfacial Thickness Characterization and Tensile Properties of Calcium-Silicate-Hydrate/Calcium Hydroxide Composites via Molecular Dynamics Simulations

Abstract

As the main hydration products, calcium-silicate-hydrate (C─ S─ H) and portlandite (CH) contribute significantly to the tensile strength of cementitious materials. However, the role of interface in the C─ S─ H/CH composites remains unexplored. This paper aims at elucidating the interfacial tensile properties of C─ S─ H/CH composites via molecular dynamics simulations with the ReaxFF forcefield. A method quantifying the thickness of the atomic-level interfacial transition zone in composites through potential energy analysis was proposed, with the value of 1.75–3.38 nm. Results showed that all models had damages at or near the interfaces. The tensile strength of composites relied highly upon material orientations. Elevated loading speed enhanced the tensile strength of composites, and their strain rate sensitivity was more significant than either C─ S─ H or CH. Failure mechanisms were revealed via chemical bond evolution. A nanoscopic tensile constitutive model was formulated based on Morse potential function. This research sheds light on the role of the interfacial area in two-phase composites at the atomic scale, which provides essential inputs for further multiscale studies.