# On the Stability of Graphene-Based Aqueous Dispersions and Their Performance in Cement Mortar
###### Abstract  
Cement composites containing different carbon nanomaterials, namely graphene technical grade, graphene super grade, and graphene oxide, up to 1.0% by weight of cement, were prepared. Ultrasonic, chemical, and thermochemical treatments were applied to improve the stability of the dispersions containing the graphene-based nanomaterials. Their exfoliation was analyzed using Raman spectroscopy, and the stability of the dispersions was quantitatively investigated by means of the static multiple light scattering (SMLS) technique. The sonication process enhanced the intensity of the 2D band of graphene technical grade, suggesting a partial degree of exfoliation, while the hydrothermal treatment with sodium cholate significantly promoted the stability of its dispersion. The effect of the addition of selected graphene-based nanomaterials in mortars was evaluated in terms of fresh state properties, mechanical strength, capillary water absorption, and pore size distribution. Workability decreased with the increase in the amount of carbon nanomaterials. Field emission scanning electron microscopy (FESEM) was also employed to characterize the microstructure of pristine graphene-based nanomaterials and their inclusion within the cement matrix. Our results suggest that mechanical properties are only moderately affected by the inclusion of all additives, whereas the introduction of graphene significantly influences the coefficient of capillary water absorption. Specifically, a reduction of about 20% in the capillary water absorption coefficient was observed at the concentration of 1.0 wt% of graphene technical grade, which is ascribed to a refinement of the porosity. graphene; cement mortars; capillary water absorption; porosimetry 202520255835 nanofibers and carbon nanotubes, can contribute to the toughness and tensile strength of mortars and concrete through crack-bridging. However, they are characterised by a limited surface area that inhibits the nucleation of calcium silicate hydrated (C-S-H) gel on them, thus negatively affecting their strength [14]. Two-dimensional (2D) carbon nanomaterials, such as graphene (Gr) and graphene oxide (GO), are characterised by a large specific surface area (SSA) [6; 15; 16], high mechanical properties [6; 17; 18], excellent thermal conductivity [19], and high electron mobility [20; 21; 22]. They can provide both nucleation sites and a bridging effect. Based on these peculiar properties, Gr and GO have been used to produce reinforced, self-sensing, and thermally conductive concrete [22; 23]. The incorporation of Gr or GO has primarily been employed to improve the mechanical properties (such as compressive strength and flexural strength) of cementitious materials, yielding varied and often not uniform results in terms of efficiency [6; 18; 24]. Several studies reported an increase of mechanical properties of cementitious materials by adding up to 0.1 wt% of Gr or GO [25; 26]. A higher amount of Gr and GO have been used to provide cement-based composites with electrical and thermal properties, but a decrease in mechanical strength was observed, most likely due to the agglomeration of carbon nanomaterials generated by non-homogeneous dispersion of graphene nanoplatelets (GNPs) [27; 28]. It is well known that treatments are necessary to improve the homogeneous dispersion of graphene nanomaterials and to promote their stability and exfoliation. The liquid phase exfoliation (LPE) of different carbon nanomaterials does not occur spontaneously in unsuitable solvents such as water, where the material-solvent interactions do not overcome the interlayer van der Waals attractive forces as well as the \(\pi-\pi\) interactions to form stable dispersions. Therefore, external energy is necessary to promote the exfoliation of the layers. Several energy sources have been proposed so far, such as ultrasonication, wet ball milling, and microfluidization [29]. Ultrasonication generates power shockwaves and produces normal and shear forces on successive layers of the materials [30].