Synthesis of a novel graphene oxide/belite cement composite and its effects on flexural strength and interfacial transition zone of ordinary portland cement mortars

In order to address the size mismatch between nanoscale graphene oxide and micron-scale ordinary portland cement (OPC), a novel graphene oxide/belite cement (GO/BC) composite hydrated for different periods was synthesized and applied to OPC-based mortar specimens. The morphology, surface area and pore size distributions of hydrated GO/BC composites were characterized. Thermogravimetric analyses and X-ray photoelectron spectroscopy (XPS) test were carried out to investigate the relative amount of different phase assemblages in the composite and possible chemical interactions between graphene oxide and belite cement, respectively. Moreover, the effects of GO/BC composite addition on the flexural strength, the porosity and thickness of ITZ in the OPC-based mortars were examined. Experimental results showed that the GO/BC composite after 14 and 21 days of curing exhibited some flower-like hydration products with ‘petals’ sizing around several microns and a large surface area. The hydrated GO/BC composite after 14 and 28 days, for 14-day in particular, is more effective in elevating the flexural strength and densifying the ITZ region of OPC-based binders, compared to the graphene oxide or belite cement alone. Thus, hydrated GO/BC composites could be served as a better nucleation seed for promoting the hydration of OPC due probably to their greater surface area, suitable sizes and chemical interactions between graphene oxide and belite cement.