# Potential of Advanced Consolidants for the Application on Sandstone
## 3 Results and Discussion
### Application of the Consolidants on the Sandstone
#### 3.3.2 Mechanical Testing in Microscale  
The direct determination of the location of the consolidant xerogel within the porous system of the sandstone and the measuring of its mechanical properties was carried out by nanoindentation. The consolidant was applied on the stone by capillary suction. To localize the consolidant, a series of indents (applied stress of 1 mN) were performed to identify a xerogel deformation pattern. The contact depth for the mineral grains in the sandstone, SiGel-d consolidant and a soft epoxy resin was ca. 100, 180 and 500 nm, respectively.  
On the stone, The SiGel-d xerogel formed a thin layer, which corresponded to the Young's modulus and hardness of 11.40 GPa and 0.93 GPa, respectively. Furthermore, the xerogel penetrated through the porous system and was detected in the lowest point of 700 \(\upmu\)m, in which the Young's modulus and hardness was 10.97 and 0.74 GPa, respectively. Regarding the SiGel-oa, the xerogel was not observed on the sandstone surface. First deposits of the xerogel were located in the depth of 250 \(\upmu\)m. Concerning this xerogel, the contact depth was ca. 300 nm, which was higher compared to the SiGel-d. The probable explanation is the better penetration of the SiGel-oa consolidant and the higher compliance of the xerogel formed due to the presence of wider mesopores in comparison with the narrower micropores of the SiGel-d xerogel.  
Compared to the pristine SiGel-oa and SiGel-d xerogels, their counterparts localized in the pores of the stone exhibited a roughly two-fold increase in the Young's modulus. This difference may be due to a confinement effect of the pore walls [22; 23; 24; 25; 26], which may increase the Young's modulus owing to the wrapping of the gel by hard stone material. Considering the hardness, however, no such increase was observed. This observation implies that the microstructure of the xerogel was not influenced by  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sandstone Treatment** & **Consolidant Uptake/ wt.\%** & **Dry Matter Yield/ wt.\%** & **Water Uptake/ wt.\%** \\ \hline Untreated & - & - & \(11.60\pm 0.5\) \\ SiGel-oa & \(10.1\pm 0.5\) & \(4.0\pm 0.2\) & \(0.09\pm 0.01\) \\ SiGel-SiO\({}_{2}\)-oa & \(8.0\pm 0.4\) & \(4.3\pm 0.2\) & \(0.06\pm 0.01\) \\ SiGel-SiO\({}_{2}\)-methyl-oa & \(10.3\pm 0.5\) & \(4.2\pm 0.3\) & \(0.12\pm 0.02\) \\ SiGel-SiO\({}_{2}\)-octyl-oa & \(9.2\pm 0.4\) & \(4.8\pm 0.3\) & \(0.12\pm 0.01\) \\ SiGel-TiO\({}_{2}\)-oa & \(10.1\pm 0.6\) & \(4.8\pm 0.4\) & \(0.11\pm 0.01\) \\ SiGel-ZnO-oa/d & \(10.2\pm 0.6\) & \(3.7\pm 0.2\) & \(0.32\pm 0.02\) \\ HAP & \(13.9\pm 0.7\) & \(0.24\pm 0.03\) & \(9.8\pm 0.5\) \\ HAP+Ca(OH)\({}_{2}\) & \(10.8\pm 0.5\) & \(0.31\pm 0.03\) & \(9.8\pm 0.6\) \\ KSE OH & \(10.6\pm 0.4\) & \(2.7\pm 0.11\) & \(2.3\pm 0.1\) \\ SP FX & \(9.6\pm 0.4\) & \(1.1\pm 0.05\) & \(9.5\pm 0.5\) \\ \hline \hline \end{tabular}
\end{table}
Table 5: Sandstone uptake by capillary suction.  
the presence of pore walls, which is a reasonable conclusion provided there was no formation of the chemical bonds between the gel and the surface of the pore walls.