Dispersion and stability of graphene nanoplatelet in water and its influence on cement composites

•A facile approach was proposed to disperse and stabilize graphene in water.•The optimum combination of superplasticizer and sonication was determined.•The stabilization mechanism of graphene was illustrated.•1% graphene can effectively increase the hardness and refine the pore structures. Cement nanocomposites were fabricated by slight modification of existing casting method to introduce graphene nanoplatelet (GNP) into cement paste. Dispersant dosage and ultrasonication time were varied to seek the optimum dispersion effectiveness. The stability of sonicated GNPs in suspension was assessed quantitatively by light absorbance over time and results suggested that 1 h of sonication and 15% of surfactant was sufficient to produce a 1% GNP suspension that remains stable for 6 h. Particle strengthening effect was obtained through the strong physical bond at the graphene interface, which was reflected by the doubling of the hardness. Mercury intrusion testing indicated that GNP could reduce the effective porosity and refine the critical pore diameter, particularly at the concentration of 1% GNP where reductions of 37% and 30% on the effective porosity and critical pore diameter were found respectively.