Effect of graphene oxide on mechanical properties, piezoresistivity and microstructure of cement mortar blended with multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) can strengthen and toughen cement-based materials. However, MWCNTs tend to agglomerate in cement paste. Up to now, there are few reports about how to improve the dispersion of MWCNTs by graphene oxide (GO) in cement paste. The effect of GO on the dispersion of MWCNTs in saturated calcium hydroxide solution (CH) used for simulated cement pore solution in the presence of sodium lignosulfonate (MN) was investigated by absorbance test, and the effects of GO on the mechanical properties, electrothermal properties, resistivity and pressure sensitivity of mortars containing MWCNTs were studied. The absorbance test shows that when the mass ratio of MN, GO and MWCNTs is 3∶1∶9, the dispersion of MWCNTs reaches the best. The mechanical properties test shows that when the optimal contents of MWCNTs and GO are 0.45wt% and 0.05wt% by the cement mass respectively, the 28 days flexural and compressive strength of the specimens are increased by 27.3% and 20.9%, the resistivity is reduced by 18.2%, and the resistance change rate is increased by 72.6%. The microstructure test shows that GO could further promote the dispersion of MWCNTs in cement-based materials, accelerate the hydration process of cement, densify the structure of cement paste. The synergy of GO and MWCNT increases the mechanical and durability and self-sensing properties of the cement mortar. In this study, the method to disperse MWCNT assisted by GO can be further extended to other carbon-based nano-reinforcing agents, and provides a new way for the development of self-sensing and intelligent cement-based materials.