Theoretical Elastic Constants of Tobermorite Enhanced with Reduced Graphene Oxide through Hydroxyl vs Epoxy Functionalization: A First-Principles Study

Graphene-based materials are considered excellent candidates to implement cementitious nanocomposites due to their mechanical properties. This paper presents a comprehensive interface interaction that ends up with computing the elastic properties for four models of the C-S-H gel, taking tobermorite 14 Å as an example, with reduced graphene oxide (rGO) to form reinforced (tobermorite) cementitious nanocomposites within the density functional theory. We found that upon relaxing the model structures, the dissociation of hydroxyl functional groups from the hydroxyl/rGO lattice occurs not only in the presence of Ca²⁺ ions to compensate for local charges but even when the Ca²⁺ charges are compensated with hydroxyl groups. In contrast, rGO/CSH interactions remained close to the initial structural models of the epoxy rGO surface. The elastic constants showed high improvements for the cementitious nanocomposite of tobermorite 14 Å with intercalated hydroxyl/rGO layers. Thus, the bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio increased up to limits set as 165, 128, 134, and 15% compared to tobermorite 14 Å, respectively. In more detail, the specific values of the elastic constants were influenced by the interface, specifically the presence of hydroxyl or epoxy groups as well as how the charges of the Ca²⁺ ions were compensated. These findings are of interest for the design of future experiments that will help to engineer better rGO/cement composites.