# Dispersion and Pressure Sensitivity of Carbon Nanofiber-Reinforced Polyurethane Cement
## 2 Materials and Methods
### Preparation of CNFPUC Specim  
First, the CNF was dried to a constant weight at 120 \({}^{\circ}\)C, to remove the moisture absorbed during storage. Next, the surface of the CNF underwent oxidation treatment, in which they were immersed in a mixture of concentrated sulfuric acid and concentrated nitric acid (1:3 by volume) for 2 h and subsequently washed in clear water and dried at 120 \({}^{\circ}\)C. Using a high precision electronic scale (Diheng Electronics Co., Ltd., Shenzhen, China) (accurate to 0.001 g), the CNF was accurately weighed, added into the prepared polyol and dispersed by the scientz-750f ultrasonic dispersion instrument (Ningbo Xinzhi) for 1 h at 60 \({}^{\circ}\)C. Second, the polyols mixed with the CNF was dewatered at 120 \({}^{\circ}\)C for 2 h (vacuum degree was 0.1 MPa) and rapidly added into the weighing cement; next, they were dried at 200 \({}^{\circ}\)C for 2 h. Subsequently, they were put into the JJ-5 type planetary cement mortar mixer (Construction Engineering Test equipment Co., Ltd., Wuxi, China) at a low speed rotation for 30 s; later the isocyanate was added evenly and stirred at a high speed for 60 s and silica fume was slowly added in a stirring process. Finally the stirred CNFPUC was poured into the mold coated with a few mold-release agents. Continuous vibration was needed during the molding process in order for the bubbles to gather and escape. After 24 h, the mold was knocked out and cured at room temperature for 3 days. The experimental temperature was 14-17 \({}^{\circ}\)C and the relative humidity was 30-50%. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline
**Chemical Composition** & **CaO** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **MgO** & **SO\({}_{3}\)** & **Na\({}_{2}\)O** & **K\({}_{2}\)O** & **Cl** & **f-CaO** & **Loss** \\ \hline Percentage of mass (\%) & 60.19 & 20.58 & 5.58 & 2.84 & 2.47 & 2.18 & 0.18 & 0.48 & 0.03 & 1.94 & 4.04 \\ \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of cement. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**Purity** & **Diameter** & **Length** & **Draw Ratio** & **Resistivity** & **Thermal** & **Thermal** & **Specific** & **Stacking** & **Density** \\ \hline
99.9\% & \begin{tabular}{c} 150–200 \\ nm \\ \end{tabular} & 10–20 & 70 & \
\begin{tabular}{c} \(6\times 10^{-6}\) \\ \(\Omega\)-m \\ \end{tabular} & 1.0 & 2000 W/m & 300 m\({}^{2}\)/g &
\begin{tabular}{c} 0.18 \\ \(\mathrm{g/cm^{3}}\) \\ \end{tabular} & 2 \\ \hline \end{tabular}
\end{table} 
Table 2: Physical parameters of carbon nanofiber. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**Chemical Composition** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **MgO** & **CaO** & **Na\({}_{2}\)O** & **pH Average** \\ \hline Percentage of mass (\%) & 85–96 & 1.0 & 0.9 & 0.7 & 0.3 & 1.3 & neutral \\ \hline \end{tabular}
\end{table} 
Table 3: Chemical composition of silica fume. Measurement  
In this study, the percolation threshold of the CNFPUC composite was determined by the percolation curve of the resistivity and the fiber content. To ensure that the fluidity of the CNFPUC satisfied engineering requirements, the collapse degree of CNFPUC was controlled to be approximately 80 mm by adjusting the poly-ash ratio [24] (polyol, isocyanate, cement and mass ratio). The surface of the cured specimen was polished to remove the dirt and oxide layer of the surface and the two parallel surfaces of the specimen were required to be polished and leveled. Next, we coated 1 mm thick conductive silver glue and pasted the electrode, which is a 10 mesh copper mesh (size: 12 mm \(\times\) 20 mm) and it was fixed using conductive tape. Subsequently, the specimen's static resistivity was tested. The size of the specimen as shown in Figure 1a is 17 mm \(\times\) 17 mm \(\times\) 17 mm.