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There has been increasing interest in using nanosized fillers in cement-based construction materials to upgrade mechanical properties, durability, and multi-functionality. In this context, graphene oxide (GO) is proved to be an effective candidate, and its interaction with cement can lead to remarkable enhancement in its macro-properties. To guarantee reproducibility and to maximize environmental and health safety, a GO water suspension (GONan, Nanesa, Italy) was selected from the market-available products. A complete morphological, microstructural and chemical characterization was performed by Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy, Infra-Red Spectroscopy (FTIR-ATR), X-ray Diffraction (XRD), and Thermogravimetric Analysis. The aggregation test of GONan in saturated Ca(OH) 2 water solution was also performed, and results were obtained by UV-VIS spectroscopy and Scanning Electron Microscopy (SEM). Different dosages (0.01%, 0.1%, and 0.2% by weight of cement) of GONan were added to a commercial M5 mortar. Fresh properties were determined by rheology measurements and flowability and workability tests. Samples were hardened in water at room temperature (RT) for 7, 14, and 28 days. The compressive and bending strength of all samples were evaluated following the standards. The microstructural features of nanocomposites hardened at 28 days were investigated by SEM. Results clearly evidenced that the extra-low GONan dosage (0.01%) was the most promising formulation. Despite the worsening of fresh properties (i.e., increase of plastic viscosity and decrease of flowability and workability by 150%, 50%, and 100%, respectively, compared to the control sample), the mechanical properties of such an extra-low dosage nanocomposite at 14 days showed a notable increase of 20% and 40% for bending and compressive strength, respectively. [ABSTRACT FROM AUTHOR]