The effect of compatibility and dimensionality of carbon nanofillers on cement composites

Carbon-based nanofillers (NFs) have a marked effect on the mechanical and rheological properties of polymeric and cementitious composites. In this study, we explored the role of four nanocarbon materials as NFs, namely, graphene nano-platelets (GNP) and carbon nanotubes (CNT) and their hydrophilic derivatives, graphene oxide (GO) and functionalized CNT (f-CNT), respectively. We investigated how the NF dimensionality and hydrophilicity affect the various properties of NF-cement composites in fresh (e.g., workability) and hardened (e.g., strength) states. This will enable one to judiciously choose an appropriate NF for a specific application. In that respect, the additive polycarboxylate ether (PCE) is employed both as a surfactant for the NF dispersion in the cementitious matrix and as a superplasticizer, reducing the composite mixture viscosity to enhance its workability. The addition of GO, CNT or f-CNT fillers (in the presence of 0.2 wt% PCE) demonstrated workability deterioration for all NF concentrations while that of the GNP-loaded system was much less affected. Among the four explored NF-loaded systems, GO (0.025 wt%) was the best reinforcing agent with enhancement of 60% in flexural and ~30% in compressive strengths. Nevertheless, GNP presents a cost-effective alternative, although a little inferior to GO in its mechanical performance.