Hydroxylated Graphene: A Promising Reinforcing Nanofiller for Nanoengineered Cement Composites

[Image: see text] A very low dosage of graphene oxide (GO) can enhance the mechanical durability of cement composites, but the reinforcing enhancement is highly dependent on the uniform dispersion of graphene in the matrix. Carboxylic groups at GO nanosheets have a decisive effect on GO aggregation in an alkaline cement solution because they have a strong complexation ability with aqueous Ca(2+) released by cement hydration and subsequently crosslinks the adjacent graphene sheets, causing the immediate coagulation of GO. The available methods of homogeneously dispersing GO in a cement slurry cannot completely eliminate this carboxylic-crosslinking-induced GO coagulation. In this study, many hydroxyl groups were introduced onto the edge and planar nanosheets to prepare water-soluble hydroxylated graphene (HO-G) by facile ball milling. The structure of HO-G was thoroughly characterized in detail, and its dispersion behavior in pure water and Ca(OH)(2) was extensively investigated. These results showed that the prepared HO-G exhibited good hydrophilicity and excellent colloidal dispersion ability against high pH and Ca(2+) ions compared to GO. The effect of HO-G on the workability, mechanical strength, and chloride penetrability of a cement mortar was further studied. At a content of 0.03% by cement mass, HO-G provided 28.62 and 21.19% enhancements of compressive strength and 3.85 and 7.89% enhancements of flexural strength at 3 and 28 days, respectively, while the non-steady-state migration coefficient decreased by 31.51% compared to the reference mortar. Compared to GO, a lower dosage of HO-G exhibited a similar reinforcing effect to cement composites with little adverse impact on the fluidity of the fresh cement slurry. Moreover, the addition of HO-G could refine the pore structure, accelerate the hydration process of cement to some degree, and generate more hydration products so that the structure of the cement mortar was densified. Considering its environmentally friendly preparation, HO-G, as a promising reinforcing nanofiller, could provide a new solution to develop nanoengineered cement composites.