Positive synergistic effect of superplasticizer stabilized graphene oxide and functionalized carbon nanotubes as a 3-D hybrid reinforcing phase on the mechanical properties and pore structure refinement of cement nanocomposites

The current investigation presents the superior mechanical performance of polycarboxylate ether based superplasticizer (PCE-SP) stabilized hybrid carbon nano-materials (HCNs) over individual GO (graphene oxide) or FCNTs (functionalized carbon nanotubes) as reinforcing agent in the cement nanocomposites (CNCs). Superplasticizer (SP) stabilized nanomaterials (SP-GO, SP-FCNT and HCNs) exhibit a good dispersion behavior in aqueous as well as alkaline environment of cement pore solution. The increased dispersion of HCNs due to SP steric stabilization as compared to GO or FCNTs has been monitored by UV-Visible spectroscopy. The compressive strength enhancement for HCN-CNCs (at 0.02% loadings by weight percentage of cement) was found to be 43.08% which was superior to strength improvements of 27.39% and 17.82% by GO (0.02%) and FCNTs (0.08%), respectively, in comparison to control at 90 days of curing. On the other hand, split tensile strength for HCNs incorporated mortar was found to be 52.20% at dosage of 0.08%. While, GO-CNCs and FCNT-CNCs showed a maximum improvement in tensile strength by 37.97% and 37.21% at loadings of 0.04% (bwoc) at curing age of 90 days. The improved degree of hydration of silicates in case of HCN-CNCs has been shown by appearance of flower-shaped regular hydration patterns and better quantity of hydration products formation as compared to control sample as observed by FE-SEM (field emission-scanning electron microscope) and XRD (X-ray diffraction) studies, respectively. In addition to this, Mercury Intrusion Porosimetry (MIP) studies showed reduction in porosity by 25.2%, 31.0% and 46.5% for FCNT-CNCs, GO-CNCs and HCN-CNCs respectively, in comparison to control. (C) 2019 Elsevier Ltd. All rights reserved.