## 3 Experimental Results  
The compressive strength testing results for each scenario and diameter at the age of seven days are illustrated in Table 7. It can be observed that the C\({}_{\text{CC}}\) columns for 110, 160, and 220 mm of diameter provide the highest compressive strength compared to C\({}_{\text{u}}\) and C\({}_{\text{c}}\) columns due to lateral confining of C\({}_{\text{CC}}\) columns which increases the load-bearing capacity, and the tube cutting ends help to restrict the tube function for confining only. However, with a 250 mm diameter, the improvement of compressive strength in C\({}_{\text{CC}}\) columns are less than in C\({}_{\text{c}}\) columns leading the latter to provide higher compressive strength. On \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample’s Radius (mm)**} & \multirow{2}{*}{**Unconfined Sample (C\({}_{\text{u}}\))**} & \multirow{2}{*}{**Fully Confined Sample (C\({}_{\text{C}}\))**} & \multirow{2}{*}{**Confined with End Cutting**} & \multirow{2}{*}{**Sample (C\({}_{\text{CC}}\))**} \\ \cline{2-2} \cline{5-7}  & \multicolumn{1}{c}{**7 Days**} & \multicolumn{1}{c}{**28 Days**} & \multicolumn{1}{c}{**7 Days**} & \multicolumn{1}{c}{**28 Days**} & \multicolumn{1}{c}{**7 Days**} & \multicolumn{1}{c}{**28 Days**} \\ \hline
110 & 3 & 3 & 3 & 3 & 3 & 3 \\ \hline
160 & 3 & 3 & 3 & 3 & 3 & 3 \\ \hline
220 & 3 & 3 & 3 & 3 & 3 & 3 \\ \hline
250 & 3 & 3 & 3 & 3 & 3 & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Distribution of specimens for each scenario, diameter and curing period. Figure 4: Mechanical mixture with 1 m\({}^{3}\) capacity. Figure 5: Casted specimens. the other hand, the C\({}_{\rm c}\) columns provide better compressive strength than C\({}_{\rm u}\) columns for all diameters due to the full confining of the column, which causes the applied load to be distributed on both the concrete and the PVC tube. However, this distribution of force limits some of the confining functionality of C\({}_{\rm c}\) columns, which affects the loading bearing capacity of the columns. Table 8 shows the enhancement due to the PVC tube confinement for both C\({}_{\rm c}\), and C\({}_{\rm CC}\) types. The improvement reaches the highest (15% for C\({}_{\rm CC}\) and 8.3% for C\({}_{\rm c}\) columns) when the column diameter is 110 mm and starts to decrease as the diameter increases. The compressive strength results at 28 days are presented in Table 9 and Figure 6. The results showed that the C\({}_{\rm CC}\) columns yield the highest compressive strength compared to C\({}_{\rm c}\) and C\({}_{\rm u}\) columns for all diameters except at 250 mm where C\({}_{\rm c}\) columns yielded slightly higher compressive strength than C\({}_{\rm CC}\) columns. Furthermore, the percentage of enhancement using PVC tubes is presented in Table 10. According to Table 10, the highest enhancement is achieved at the diameter of 110 mm, reaching a percentage of 15% for C\({}_{\rm CC}\) and 8.3% for C\({}_{\rm c}\) columns, then starting to decline as the diameter increases. Tables 8 and 10 show that using PVC tubes enhanced the short columns' compressive strength by the same ratio by seven and 28 days. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample’s Radius** & **Strength of Cu** & \multirow{2}{*}{**Strength of Cc (MPa)**} & **Strength of Ccc (MPa)** \\
**(mm)** & **(MPa)** & & **(MPa)** \\ \hline
110 & 10.8 & 11.7 & 12.41 \\
160 & 11.1 & 12 & 12.5 \\
220 & 12.09 & 12.81 & 13.56 \\
250 & 13.44 & 14.11 & 14 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Compressive strength at the age of 7 days. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample’s Radius (mm)** & **Improvement Using Cc \%** & **Improvement Using Ccc\%** \\ \hline
110 & 8.3 & 15 \\
160 & 8.1 & 12.61 \\
220 & 6 & 12.16 \\
250 & 5 & 4.16 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: The improvement of compressive strength using PVC tubes at 7 days. Figure 6: Comparison between each scenario in terms of compressive strength at 28 days.