## 2 Materials and Methods
### Specimens Treatment  
Unconfined compressive strength is an important index to evaluate the mechanical properties of grout-reinforced specimens. In this experiment, the unconfined compressive strength of grout-reinforced specimens is used as an index to analyze the original grout-reinforced specimens, the grout-reinforced specimens after soaking in an acidic solution, and the grout-reinforced specimens after a freeze-thaw cycle in an acidic environment.  
Firstly, the drying test of the cured grout-reinforced specimens is carried out. The electric blast drying oven is used to dry the specimens. The working principle is to heat the air inside the equipment, then use the fan to make the air circulate inside and outside the object to be dried for heat exchange, and finally make the object to be dried or dried. A total of 60 specimens were placed in a drying oven for drying. The drying temperature was set at 105 \({}^{\circ}\)C, and the drying time was 24 h. The quality of grout-reinforced specimens was measured by a high-precision electronic scale after drying.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Setting Time (min)**} & \multicolumn{5}{c}{**Water–Material Ratio**} \\ \cline{2-7}  & **0.3** & **0.4** & **0.5** & **0.6** & **0.7** \\ \hline \multirow{2}{*}{FCM} & Initial & 40 & 47 & 55 & 63 & 98 \\  & Final & 75 & 77 & 80 & 90 & 108 \\  & Initial & 200 & 240 & 330 & 410 & 480 \\  & Final & 380 & 450 & 530 & 600 & 660 \\ \hline \hline \end{tabular}
\end{table}
Table 4: The effect of water–material ratio on setting time of FCM and P.O 42.5 slurry.  
Figure 3: Fracture-grout-reinforced specimens: (**a**) grouting process.; (**b**) full-penetrated fracture specimens.; (**c**) semi-penetrated fracture specimens.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Fluidity (cm)**} & \multicolumn{5}{c}{**Water–Material Ratio**} \\ \cline{2-5}  & **0.3** & **0.4** & **0.5** & **0.6** & **0.7** \\ \hline FCM & 33.5 & 36 & 42 & 45 & 47.5 \\ P.O 42.5 & 6 & 8.5 & 15.75 & 24 & 28.4 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The effect of water–material ratio on the fluidity of FCM and P.O 42.5 slurry.  
Secondly, the acid solution with pH = 1 was prepared by hydrochloric acid with a concentration of 1 mol/L, and the specimens were immersed in it. After soaking for 7 days, the specimens were taken out, and the surface water was dried and weighed. The freeze-thaw test was carried out by GDW225 high- and low-temperature alternating test chamber after wrapping the fresh-keeping film in some patterns. According to the literature [36], the freeze-thaw cycle temperature was set at 20-20 \({}^{\circ}\)C, the freezing time was 4 h, the melting time was 4 h, and the first cycle was 8 h. The number of cycles was set to 5, 10, 20, and 30 times. After the freeze-thaw cycle, the wrapped preservation film was removed, and the quality was weighed and put into the oven for drying.  
Finally, the YZW-30 A multifunctional testing machine was used to test the compressive strength of the specimens, and the unconfined compressive strength and failure mode were obtained. The test flow is shown in Figure 4.