# On the Stability of Graphene-Based Aqueous Dispersions and Their Performance in Cement Mortar
## 2 Materials and Methods
### Exfoliation Pretreatment  
Given the hydrophobic nature of Gr-TG and Gr-SG, a two-step process was proposed and implemented to improve their exfoliation and prevent the layers from restacking. It was characterized by an initial hydrothermal treatment (HT), aided by the addition of surfactant SC, followed by ultrasonication.  
Water dispersions were prepared by mixing water, Gr-TG, or Gr-SG with surfactant SC. The prepared dispersions were initially mechanically stirred at 100 rpm for 5 min. The final graphene-based nanomaterial concentration was fixed at 1.53 wt% or 2.50 wt% on water. Surfactant SC to Gr-TG (or Gr-SG) mass ratio was fixed at 1/5. After stirring, each dispersion was poured into autoclaves (volume of 50 cm\({}^{3}\)) and heated at a rate of 1.5 \({}^{\circ}\)C/min up to the set point temperature, which was fixed at 180 \({}^{\circ}\)C, and kept at this temperature for 6 h. Finally, the dispersions were ultrasonicated in a SOLTEC-SONICA M S3 bath ultrasonicator (40 kHz, 80 W) for 6 h before being used in the production of mortars. In order to prevent overheating, the beakers were placed in a cold water bath during ultrasonication. The dispersions containing GO were prepared by mixing water and GO. The prepared dispersions were initially mechanically stirred at 100 rpm for 5 min. The final GO concentration was fixed equal to 1.53 wt% or 2.50 wt% in water. After stirring, GO dispersions were ultra-sonicated in a Soltec-Sonica M S3 bath ultrasonicator (40 kHz, 80 W) for 6 h before being used in the production of mortars. In order to prevent overheating, the beakers were placed in a cold water bath during ultrasonication. The composition of all the prepared graphene-based dispersions and operational details of each treatment are summarized in Table 2. Water dispersions with concentration equal to 1.53 wt% were then used to produce mortars containing up to 0.3 wt% of graphene-based nanomaterials. It  
\begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline
**Raw** & \multicolumn{4}{c}{**Characteristics**} \\
**Materials** & & & & & & & & \\ \hline Cement & \multicolumn{4}{c}{Manufactured in accordance to standard UNI EN 197-1. Main Components, in terms of oxides:} \\  & \multicolumn{4}{c}{SiO\({}_{2}\) = 18.61 wt\%; Fe\({}_{2}\)O\({}_{3}\) = 2.87 wt\%; Al\({}_{2}\)O\({}_{3}\) = 4.38 wt\%; CaO = 60.60 wt\%; MgO = 3.16 wt\%;} \\  & \multicolumn{4}{c}{K\({}_{2}\)O = 0.79 wt\%; Na\({}_{2}\)O = 0.35 wt\%; MnO = 0.17 wt\%; SO\({}_{2}\) = 2.83 wt\%; TiO\({}_{2}\) = 0.2 wt\%.} \\  & \multicolumn{4}{c}{Particle size distribution, based on volume distribution: D\({}_{10}\) = 8.414 \(\mu\)m; D\({}_{80}\) = 19.84 \(\mu\)m;} \\  & \multicolumn{4}{c}{Do\({}_{0}\) = 36.11 \(\mu\)m.} \\ \hline
**Additive** & \multicolumn{4}{c}{_SSA_ **(m\({}^{2}\)/g)** & **Thickness** & \multicolumn{4}{c}{**Lateral**} & \multicolumn{4}{c}{**Bulk**} \\
**type** & \multicolumn{4}{c}{**(m\({}^{2}\)/g)**} & \multicolumn{4}{c}{**(nm)**} & \multicolumn{4}{c}{**size**} & \multicolumn{4}{c}{**(g/cm\({}^{3}\))**} & \multicolumn{4}{c}{**C**} & \multicolumn{1}{c}{**O**} & \multicolumn{1}{c}{**S**} \\ \hline Gr-TG & 80 & 10–20 & 10 \(\mu\)m & 0.25 & \(>\)99 & \(<\)1 & \(<\)1 \\ Gr-SG & \(>\)250 & 1.6 & 6–100 nm & 0.06 & \(>\)99 & 0 & 0 \\ GO & 350 & 10–20 & \(<\)10 \(\mu\)m & 0.35 & 74 & 25 & 0.34 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Physical and chemical properties of raw materials used for mortar specimens. The elemental composition shows, in percentage, the main elements reported by the manufacturer: carbon (C), oxigen (O), and sulphur (S).  
Figure 1: Sand gradation.  
worthy to be noted that it was necessary to use water dispersions with concentration equal to 2.50 wt% to produce mortars in the range of 0.5-1 wt% to comply with the fixed w/c ratio selected for the mix design (see Table 3).