Investigation on chloride binding capacity and stability of Friedel's salt in graphene oxide reinforced cement paste

Chloride binding capacity is one of the important factors affecting chloride induced rebar corrosion in reinforced concrete structures. Moreover, the stability of Friedel's salt will also affect the chloride binding capacity of cement-based materials. This study investigates the effect of graphene oxide (GO) on the chloride binding capacity of cement paste and stability of Friedel's salt under different pH conditions. Experiments of X-ray diffraction (XRD), Thermogravimetric analyzer (TGA), Scanning electron microscope (SEM) and Energy dispersive spectroscopy (EDS) were performed to analyze the phase assemblage, micro morphology, element ratio and the enhanced mechanisms. Results showed that the 0.2 wt% GO addition can significantly improve the chloride binding capacity of cement paste where the amount of bound chloride ions increased by approximately 46%. Meanwhile, the release of bound chloride ions at low pH conditions (from 12 to 9) can be suppressed by GO addition, which the chloride ion desorbing rates of cement-based materials dropped from 88% to 38% with 0.2 wt% GO addition. Microstructural and hydration analyses illustrated that GO addition promoted the formation of stable Friedel's salt by strong charge adsorption effect on calcium ions. Also, inhibiting the chloride ion desorbing and decomposition of Friedel's salt at low pH conditions.