## 2 Experimental Overview
### Experimental Apparatus and Equipment  
The temperature heating device is depicted in Figure 4. It consisted of an RX3 model box-type resistance furnace that could operate at up to 380 V and with an output of nearly 24 kW. The furnace temperature could rise at a rate close to 20 \({}^{\circ}\)C/min and could reach a maximum temperature of 1280 \({}^{\circ}\)C. The furnace's interior dimensions were 500 mm \(\times\) 400 mm \(\times\) 400 mm. Prism specimens were tested at 25 \({}^{\circ}\)C, 200 \({}^{\circ}\)C, 300 \({}^{\circ}\)C, 400 \({}^{\circ}\)C, 600 \({}^{\circ}\)C, and 800 \({}^{\circ}\)C, while cube specimens were tested at 25 \({}^{\circ}\)C, 600 \({}^{\circ}\)C, and 800 \({}^{\circ}\)C. The mechanical test employed a computerized data acquisition and control hydraulic servo \begin{table}
\begin{tabular}{c c} \hline \hline
**Variable Symbol** & **Variable Description** \\ \hline \(\epsilon_{\text{c,T}}\) & Peak strain \\ \(\text{f}_{\text{c,T}}\) & Peak stress \\ \(\text{E}_{\text{c,T}}\) & Elastic modulus \\ \(\text{v}_{\text{c,T}}\) & Poisson’s ratio \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._  
Figure 3: Three dimensional drawing of sample size. universal testing machine with a 30 t capacity, as shown in Figure 5. Before conducting the uniaxial compression test, transverse and longitudinal strain gauges were attached to the center of the four sides of the prism specimen's long edge. The test should be performed at an air temperature of 28 \(\pm\) 3 \({}^{\circ}\)C and a humidity of 78 \(\pm\) 5%. Before the strength test, the central axis of the concrete test piece should be aligned with the compressive central axis of the press, and the upper surface of the concrete test block should be parallel to the upper pressing plane of the press to prevent eccentric damage. The compressive test's loading rate was set at 0.5 MPa/s, and the splitting tensile test was set to 0.05 MPa/s, in accordance with the relevant provisions of the Standard for Test Methods of Properties of Plain Concrete Mixes (GB/T 50080-2002) [43] and the Standard for Test Methods of Mechanical Properties of Plain Concrete (GB/T 50081-2002) [47], with reference to the methods used in [PERSON]'s test [48]. Splitting tensile test device diagram see Figure 6. To obtain more precise test results and the control test error, a force sensor was included between the test block and the indenter plane of the test machine in the uniaxial compressive test, as shown in Figure 7.  
Figure 4: RX3 model box-type resistance furnace. Figure 5: Floor plan of the universal testing machine. of the PL0C0-T200 group, while the peak strains of the PL9C1.5-T300 and PL9C1.0-T300 groups were 19.05% and 25.58% lower than that of the PL0C0-T300 group, respectively. It was observed that the peak strain did not change much between 25 \({}^{\circ}\)C and 300 \({}^{\circ}\)C, which is because, as the temperature increases, the evaporation of free water in the cement paste accelerates the hydration of the cement paste, increases the density of the C-S-H gel structure, and causes the cement paste to shrink and produce high-strength siloxane [49; 50]. The removal of free water is similar to steam curing, which accelerates the hydration of the cement, and repairs the damage inside the concrete. The reason for the lower peak strain of PPF concrete, than that of ordinary concrete, is analyzed as follows. PPF fibers melt at around 170 \({}^{\circ}\)C and vaporize at around 370 \({}^{\circ}\)C. The connecting holes formed by the melting of PPF may be transformed into micro-cracks, increasing the crack propagation path. As the temperature increases, the porosity inside the PPF concrete increases rapidly, and the crack propagation gradually transitions from micro-cracks to macro-cracks [51; 52]. Therefore, when the temperature was below 400 \({}^{\circ}\)C, the peak strain of PPF concrete was smaller than that of ordinary concrete. When the temperature reached 400 \({}^{\circ}\)C, a significant increase in peak strain was observed.