Effect of graphene oxide on the mechanical properties and the formation of layered double hydroxides (LDHs) in alkali-activated slag cement

Abstract

Due to its high aspect ratio and outstanding tensile strength, graphene oxide (GO) can dramatically reduce the brittleness of cement-based materials. In this paper, GO nanosheets were successfully synthesised using the modified Hummers’ method. Effects of the GO on the fluidity, mechanical properties of alkali-activated slag (AAS) mortars and the microstructure of the AAS pastes were studied. It is found that addition of the GO caused a significant reduction in fluidity and a slight decrease in the compressive strength of the hardened mortars. However, the GO improved the flexural strengths by 20% with a dosage of 0.01 wt% after 7 days. Large-scale layered double hydroxides (LDHs) were observed using SEM, the compositions of which were identified and EDS and XRD. A possible mechanism of the formation of LDHs in the GO-AAS system is proposed. Due to the Mg2+/Al3+ decomposed from the slag and the Al(OH)4− formed in the high pH condition in the GO-AAS system, the reaction pathway of LDHs can be regarded as aMg2++Al(OH)4-+(2a-2)OH-+xH2O+A-⇋MgaAl(OH)2+2aA·xH2O(s) This research provides a further understanding of the effect of graphene oxide which has a potential application of GO in AASC.