## 4 Conclusions  
The following conclusions were reached based on the experiments involving the use of waste concrete powder, a byproduct generated in the process of recycling waste concrete, to replace silica powder, which acts as a source of SiO\({}_{2}\) and filler during autoclave curing, in the production of extrusion panels: \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test Items** & **Performance Criteria** & **Test Result Plain/(R50)** & **Fire Resistance Plain/(R50)** \\ \hline \multirow{4}{*}{\begin{tabular}{c} Flame interruption \\ performance \\ \end{tabular} } & Penetration of crack gauge & N/A (N/A) & 120 min (120 min) \\ \cline{2-4}  & Ignition of pads surface & N/A (N/A) & 120 min (120 min) \\ \cline{2-4}  & Occurrence of flame & N/A (N/A) & 120 min (120 min) \\ \hline \multirow{4}{*}{\begin{tabular}{c} Thermal \\ interruption \\ performance \\ \end{tabular} } & Initial Temp. & - & \begin{tabular}{c} Mean 21 \({}^{\circ}\)C \\ (Mean 21 \({}^{\circ}\)C) \\ \end{tabular} & - \\ \cline{2-4}  & \begin{tabular}{c} Mean temp. \\ (non-heating \\ surface) \\ \end{tabular} & 161 \({}^{\circ}\)C & 163 \({}^{\circ}\)C (162 \({}^{\circ}\)C) & 33 min (35 min) \\ \cline{2-4}  & \
\begin{tabular}{c} Max temp. \\ (non-heating \\ surface) \\ \end{tabular} & 201 \({}^{\circ}\)C & 206 \({}^{\circ}\)C (209 \({}^{\circ}\)C) & 42 min (43 min) \\ \cline{2-4}  &
\begin{tabular}{c} Portable \\ thermocouple \\ \end{tabular} & - & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Fire-resistance tests during 120 min. Figure 12: Time vs. temperature curves in fire-resistance tests. An increase in the silica powder-WCP substitution ratio results in weakened strength, but the strengths of specimens with lower than a 50% substitution ratio surpassed the prescribed strength requirement of 14 MPa, and the strength of the specimen with a 50% substitution ratio also satisfied the requirement, which confirmed the possibility of using WCP. 2. The specimens in which WCP was used had a higher specific gravity and absorption rate when compared to the plain specimen in which only the silica powder was used, while the rate of change in length caused by water absorption was lower in the former specimens or equivalent. A review was performed in regard to the curing conditions, and the results showed that autoclave curing was essential in extrusion panel production as it not only ensured the strength of the panels, but also had an impact on density, absorption rate, and rate of change in length. The specimens containing WCP also satisfied the related standards. 3. The results of the thermal conductivity and fire-resistance tests showed that the specimens containing WCP had equivalent or superior characteristics in comparison to the plain specimens. This is deemed to be caused by the material characteristics of WCP, such as pores and bound water [19]. 4. Based on the aforementioned experimental results, it was concluded that WCP, a byproduct from the recycling of waste concrete, is an adequate material to substitute silica powder in the production of extrusion concrete panels, which essentially do not require high purity. Based on this, the application of WCP to extrusion concrete panels and various fillers is expected to contribute to the reduction of treating byproducts, which are currently buried into the ground, and to the environmental protection efforts as it will help reduce the consumption of natural resources. Additional profits are also expected for the construction waste processing firms, as value is given to WCP, the yield of which has been increasing as a result of the production of high-quality recycled aggregates.