Molecular Scale Modelling and Chemical and Mechanical Characterization of Graphene-Oxide-Reinforced Calcium Silicate Hydrate (C-S-H) Using Reactive Force Field (ReaxFF)

Graphene and graphene oxide (GO) exhibit exceptional tensile strength and elastic modulus, and the functional groups on GO promote dispersion and accelerate hydration in cementitious matrices. This study uses molecular dynamics (MD) simulations to investigate the mechanical behaviour of graphene/GO-reinforced calcium silicate hydrate (C-S-H) at the nanoscale. A reactive force field (ReaxFF) with modified C/O parameters was developed to describe atomic interactions between C-S-H and graphene/GO. A more realistic C-S-H structure with varying calcium-to-silicon (Ca:Si) ratios was produced by removing silicate chain segments from tobermorite, followed by grand canonical Monte Carlo (GCMC) simulation to introduce water molecules and hydroxyl groups. Functional groups in GO formed extensive hydrogen bonds with neighbouring water and hydroxyl groups in the C-S-H matrix. At a Ca:Si ratio of 1.7, carboxyl-functionalized GO formed the most hydrogen bonds and achieved 26% higher pull-out strength than hydroxyl- and epoxy-functionalized GO. Graphene/GO improved x- and y-direction tensile performance relative to plain C-S-H, whereas the z-direction (out-of-plane) tensile properties were lower than those of plain C-S-H. Nevertheless, GO sheets bridged disconnected C-S-H globules, giving a z-direction tensile strength of 0.15–0.59 GPa, whereas pristine and defective graphene contributed negligibly (0.003–0.03 GPa). Tailoring GO functionalization and providing adequate anchorage length are therefore key to optimizing GO-reinforced C-S-H.