Laboratory investigation of graphene oxide suspension as a surface sealer for cementitious mortars

•Graphene oxide (GO) was used as a new surface sealer for cementitious mortars.•GO could form a dense layer physically and chemically bonded to mortar surface.•GO effectively mitigated moisture loss and facilitated the hydration process.•Surface treatment by GO led to a densified microstructure of cementitious mortars.•Timing and curing condition influenced the sealing property of GO. This work investigated the influence of graphene oxide (GO) suspension as a surface sealer on the properties of two types of cementitious mortars (Portland cement mortar and high-volume fly ash (HVFA) mortar) under two curing conditions (wet curing and dry curing). Experimental results showed that GO surface treatment slightly improved compressive strength of wet cured HVFA mortar and dry cured cement mortar while it significantly reduced the water absorption of wet cured HVFA mortar and the gas permeability of both wet cured and dry cured cement mortars. Scanning electron microscopy (SEM) analysis suggested that the GO surface treatment facilitated the hydration process and densified the microstructure of both types of mortars. X-ray diffraction and Thermogravimetry results revealed the formation of hydroxyl grafted AFm phase at the interface of GO/HVFA mortar. Moreover, the GO surface treatment was found to decrease the carbonation of HVFA mortar but increase that of cement mortar.