Graphene oxide-assisted multi-walled carbon nanotube reinforcement of the transport properties in cementitious composites

The superior mechanical properties of multi-walled carbon nanotubes (MWCNTs) and prominent dispersibility of graphene oxide (GO) make their hybrid materials have the potential capability for modifying the transport properties of cementitious composites. GO sheets will produce π–π stacking interactions between MWCNTs which not only assist the dispersion but also inhibit the re-agglomeration of the materials. However, as one type of tough two-dimensional materials, GO sheets would cut down the tube length of MWCNTs at the same time, particularly during the ultrasonication process. Thereby, this study characterizes the influence of GO on the dispersion and hydrodynamic size of the hybrid particles using an ultraviolet–visible spectrophotometer and laser particle-size analyzer, respectively. The transport properties of GO/MWCNTs-OPC pastes containing different ratios of hybrid materials were measured, and their microstructure was investigated by mercury intrusion porosimetry and scanning electron microscopy (SEM). The results of this study confirm that 0.02 wt% GO mixed into 0.04 wt% MWCNTs would balance the dispersion-assisted and nanoparticle cutdown effects well and obtain the optimal decrease in resisting water permeability of the materials, about 55.3%, while excessive GO mixing may deteriorate particle-size and influence reinforcing efficiency. Two analytical models and SEM images reveal the mechanism of transport properties reinforcement; GO/MWCNTs not only play a significant role as nucleating sites in assisting the hydration reaction but also form a net-like distribution in the microstructure of cementitious composites. The findings of this study can guide GO/MWCNTs hybrid composite implementation in the future.