# Multifunctional Graphene-Concrete Composites: Performance and Mechanisms
## 3 Results and Discussion
### Impermability  
Concrete is inherently porous and hydrophilic. In practical applications, water infiltration can lead to issues such as skin peeling of walls, resulting in indoor dampness and other negative effects. Consequently, it is essential to investigate the influence of graphene on the permeability of concrete test blocks [30]. Under the combined influence of surface tension and capillary action, water ascends beyond the initial water level. The vertical distance between the initial water level and the maximum water level attained is defined as the penetration depth. As illustrated in Figure 14a, this study employed the methodology described in the literature by immersing five completely dried test blocks in water, ensuring a specified distance between the blocks. The initial water level was set 2.5 cm above the base of the test blocks. The effect of the graphene dosage on the impermeability of concrete was systematically investigated by \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Number**} & \multicolumn{2}{c}{**The Difference Between Peak Temperature of the Rear Surface and Initial Temperature (\({}^{\circ}\)C)**} \\ \cline{2-5}  & **First Test** & **Second Test** & **Third Test** & **Average Value** \\ \hline
1-4 & 17.7 & 17.8 & 17.6 & 17.7 \\ \hline
2-4 & 19.6 & 19.7 & 19.5 & 19.6 \\ \hline
3-4 & 20.1 & 20.0 & 19.9 & 20.0 \\ \hline
4-4 & 19.8 & 19.6 & 19.4 & 19.6 \\ \hline
5-4 & 16.7 & 16.9 & 16.8 & 16.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The Difference Between Peak Temperature of the Rear Surface and Initial Temperature. Figure 13: (**a**) Plot of surface temperature change over time after test block (The different line colors are only for distinguishing different test blocks). (**b**) The relationship between the difference between the peak surface temperature and the initial temperature (\(\Delta\)T) after the test block and the amount of graphene. quantifying the maximum penetration depth and the corresponding penetration area of the test specimens over a specified duration. This analysis provided critical insights into the relationship between the graphene concentration and the material's resistance to fluid ingress. Both the peak water level and the penetration depth are recorded after a 7-day period, with the maximum penetration depth denoted as \(k\) (see Figure 14b) [33]. As illustrated in Figure 14c, the surface corresponding to the maximum penetration depth (\(k\)) for each test specimen is selected as the analysis plane. The area infiltrated by water on this surface is designated as the seepage area (S). The seepage area is quantitatively assessed to facilitate a comparative analysis of the seepage performance across different test specimens, thereby elucidating the impact of graphene on the permeability resistance of concrete. The seepage area is calculated using the following formula:  
\[S=S_{1}+S_{2} \tag{1}\]  
\[S_{1}=h\cdot d \tag{2}\]  
\[S_{2}=s\cdot n \tag{3}\]  
where (S) represents the water seepage area, (\(S_{1}\)) denotes the corresponding seepage area at the initial water level, as illustrated in Figure 14c, (\(S_{2}\)) represents the seepage area after the test block was immersed in water for 7 days, showing an increase relative to \(S_{1}\), as shown in Figure 14c, (\(h\)) is the initial infiltrating height of the test block and (\(d\)) is the test block side length, (\(s\)) represents the area of a square with a side length of 1 cm, and (\(n\)) represents the number of squares in \(S_{2}\) with a side length of 1 cm. To facilitate the calculation of \(S_{2}\), we divide the region into a number of squares of area (\(s\)). Squares smaller than half of s are ignored, and squares larger than half of s are counted as 1. As shown in Table 5, the penetration depth (\(k\)) of graphene-doped test blocks is significantly lower compared to that of undoped test blocks. Moreover, the water seepage area of test blocks 2-4, 3-4, and 5-4 is markedly reduced relative to that of test blocks 1-4  
Figure 14: (**a**) Impermeability test diagram.