Sadixa Baral, Ramesh Raghavendra, Ken Thomas, Raja Das
Graphene oxide (GO) has been widely investigated as a nanoreinforcement for cementitious composites; however, its effectiveness depends on stable dispersion within the highly alkaline, calcium-rich environment of fresh cement paste. This study evaluates the dispersion behaviour of GO in deionised (DI) water and saturated calcium hydroxide (Ca(OH)2) under controlled conditions and assesses the effectiveness of anionic and cationic surfactants in both environments. GO was synthesised using the modified Hummers method and verified by comprehensive physicochemical characterisation. Dispersion stability was assessed using UV-Vis spectroscopy at GO concentrations of 0.04–0.08 mg/mL in DI water, and the 0.08 mg/mL system was further studied in saturated Ca(OH)2 with and without sodium dodecylbenzene sulphonate (SDBS) and cetyltrimethylammonium bromide (CTAB) at a 1:1 mass ratio. Zeta potential and dynamic light scattering measurements were performed to understand the relation between the surface charge and agglomeration of GO. In DI water, GO retained close to 70% of its initial absorbance after 60 min, and both surfactants improved retention to above 90%. In saturated Ca(OH)2, retention fell to approximately 40%, and neither surfactant restored stability despite producing zeta values that would conventionally support stable dispersion. The findings indicate that GO aggregation in calcium ion (Ca2+)-rich alkaline environments is not governed by net surface charge alone, consistent with the established mechanism of Ca2+ chemical cross-linking with GO carboxyl groups.