Graphene Nanoplatelet–Driven Structural Modifications in Synthetic Calcium-Silicate-Hydrate

Graphene nanoplatelets (GnPs) have shown promise in enhancing cementitious materials, yet their interaction with calcium-silicate-hydrate (C-S-H), the primary cement binding phase, remains insufficiently understood. This study examines the structural and microstructural modifications of synthetic C-S-H induced by GnPs of varying particle sizes (M15, C300, and C750) and dosages (0.03%–0.1% by weight) across calcium-to-silicon (C/S) ratios of 1, 1.5, and 2, synthesized using a modified double-decomposition method and characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). Results showed that GnPs significantly influenced C-S-H nucleation and domain evolution, with smaller GnPs (C750) reducing calcium carbonate formation and promoting more ordered C-S-H domains, whereas larger GnPs (M15) enhanced C-S-H content and increased interlayer spacing. At a C/S ratio of 1.5, C750 reduced calcite content by 12%, whereas M15 increased C-S-H content by 7%. Overall, GnPs facilitated calcium ion retention within C-S-H layers, limiting carbonation and suggesting a pathway for engineering cementitious composites with improved durability and tailored performance.