## 2 Materials and Methods
### Testing Methods  
In order to evaluate the properties of RMPC, permeability, compressive strength, flexural strength, flexural stain (flexural stain refers to the flexural stain at the peak in the following text), and freeze-thaw cycle tests were conducted in the lab. The constant head permeability test was used to determine the permeability coefficient of pervious concrete according to the national standard [32]. The temperature of the permeability test was 20 \(\pm\) 2 \({}^{\circ}\)C. A depiction of the permeability test apparatus is shown in Figure 2. In addition, water flow along the lateral side of the specimen has crucial influence on the permeability assessment, which could be eliminated by installing plasticine and plastic wrap around the specimen. The test procedures were as follows: (a) put the specimen sealed with plastic wrap around it into the permeability test apparatus; (b) seal the junction of the specimen and apparatus with plasticine; (c) inject water into the instrument until the height the of water head is constant; (d) collect permeable water in 300 s. Three parallel tests were conducted in each group. The permeability coefficient can be calculated by the following equation:  
\[k=\frac{QL}{AHt} \tag{1}\]  
where \(k\) is the permeability coefficient (mm/s); \(Q\) is the discharged amount of water in t time (mm\({}^{3}\)); \(L\) is the height of the specimen (mm); \(A\) is the upper surface area of the specimen (mm\({}^{2}\)); \(H\) is the height of water head (mm), and \(H\) = 150 mm; and \(t\) is the time (s), with \(t\) = 300 s. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Mix ID** & **Coarse Aggregate** & **Cement** & **Water** & **Superplasticizer** & **CCR** & **FCR** \\ \hline Control & 1503 & 480 & 144 & 3.84 & 0 & 0 \\ CCR-2 & 1503 & 480 & 144 & 3.84 & 9.6 & 0 \\ CCR-4 & 1503 & 480 & 144 & 3.84 & 19.2 & 0 \\ CCR-6 & 1503 & 480 & 144 & 3.84 & 28.8 & 0 \\ CCR-8 & 1503 & 480 & 144 & 3.84 & 38.4 & 0 \\ FCR-2 & 1503 & 480 & 144 & 3.84 & 0 & 9.6 \\ FCR-4 & 1503 & 480 & 144 & 3.84 & 0 & 19.2 \\ FCR-6 & 1503 & 480 & 144 & 3.84 & 0 & 28.8 \\ FCR-8 & 1503 & 480 & 144 & 3.84 & 0 & 38.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Mix ratio of pervious concrete (in kg/m\({}^{3}\)). Compressive strength and flexural strength at the age of 28 days were tested according to the national standard [33]. Three parallel tests were conducted in each group. The specimens for the permeability test were used to determine the compressive strength. Flexural strength and flexural strain were determined using a closed-loop, servo-controlled hydraulic testing system in the three-point bending mode. The distance between the two supporting points is 300 mm, and the distance from the loading point to each supporting point is 150 mm. The load and deflection of the specimen could be recorded in real time by the testing system. The load and deflection were recorded throughout the entire process; the specimen began to bear the load until it broke. The loading rate for the flexural test was set as 0.05 kN/s. The testing system is shown in Figure 3. The flexural strength and flexural strain were determined by the following equations:  
\[f_{f}=\frac{3 PL}{2 bh^{2}} \tag{2}\]  
\[\varepsilon_{f}=\frac{6h\Delta}{L^{2}} \tag{3}\]  
where \(f_{f}\) is the flexural strength of the specimen (MPa); \(\varepsilon_{f}\) is the flexural strain of the specimen; \(P\) is the failure load (N); \(L\) is the distance between the two supporting points (mm), \(L\) = 300 mm; \(b\) is the section width of the specimen (mm), and \(b\) = 100 mm; \(h\) is the height of the specimen (mm), with \(h\) = 100 mm; and \(\Delta\) is the deflection corresponding to \(P\) (mm). The freeze-thaw test was conducted according to the national standard [34]. The fast freezing method was followed to assess the freeze-thaw resistance. Three parallel tests were conducted in  
Figure 3: Closed-loop, servo-controlled hydraulic testing system. Figure 2: Permeability test apparatus. each group.