## 3 Results and Discussion
### Analysis of Orthogonal Test Results  
#### 3.1.1 Range Analysis  
The range analysis results are listed in Table 5. K represents the average value of performance indices at a certain level of factor. K1, K2, and K3 represent the average value of performance indices at the first level of factor, the second level of factor, and third level of factor, respectively. R is the difference between maximum and minimum K. The larger the R value, the greater the influence of the factor on the corresponding performance indices. In Table 5, A represents aggregate size, W/B represents water-binder ratio, and P represents porosity. The relationships between property indices and K values are shown in Figure 3.  
Figure 3a shows the influence of factors on the compressive strength of PC. Based on the size of R and K values, we can conclude that the primary and secondary order of influence factors is porosity, aggregate size, and water-binder ratio. The optimal combination is porosity 15%, aggregate size 4.75-9.5 mm, and W/B 0.25. Figure 3b shows the influence of factors on flexural strength. Based on R and K values, the primary and secondary order of the influence factors is porosity, aggregate size, and water-binder ratio. The optimal combination is porosity 15%, aggregate size 4.75-9.5 mm, and W/B 0.30. Figure 3c shows the influence of various factors on permeability coefficient. Based on R  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multicolumn{2}{c}{**Density**} & \multirow{2}{*}{**P\({}_{t}\) (\%)**} & \multirow{2}{*}{**P\({}_{e}\) (\%)**} & \multirow{2}{*}{**k (mm/s)**} & \multirow{2}{*}{**f\({}_{e}\) (MPa)**} & \multirow{2}{*}{**f\({}_{f}\) (MPa)**} & \multicolumn{2}{c}{**Freeze-Thaw**} \\  & & \multicolumn{2}{c}{**(kg/m\({}^{3}\))**} & & & & & & & & & & **Cycles** \\ \cline{2-11}  & **Mean** & **Sd** & **Mean** & **Sd** & **Mean** & **Sd** & **Mean** & **Sd** & **Mean** & **Sd** & **Mean** & **Sd** & **Mode** \\ \hline
1 & 2061 & 18 & 16.4 & 0.5 & 14.0 & 0.8 & 3.95 & 0.34 & 24.4 & 0.3 & 4.83 & 0.03 & 80 \\
2 & 1943 & 10 & 21.5 & 0.3 & 18.1 & 0.5 & 5.47 & 0.22 & 20.7 & 0.1 & 4.21 & 0.05 & 70 \\
3 & 1847 & 54 & 25.8 & 1.6 & 21.6 & 1.0 & 8.44 & 0.34 & 17.9 & 1.2 & 3.44 & 0.37 & 70 \\
4 & 1899 & 47 & 22.3 & 1.4 & 18.8 & 1.1 & 6.31 & 0.43 & 19.4 & 0.6 & 3.64 & 0.09 & 60 \\
5 & 1838 & 26 & 25.9 & 1.8 & 22.0 & 1.4 & 8.55 & 0.21 & 16.2 & 1.6 & 3.27 & 0.36 & 50 \\
6 & 2110 & 7 & 16.5 & 0.6 & 13.7 & 0.8 & 3.70 & 0.16 & 21.9 & 0.6 & 4.21 & 0.08 & 70 \\
7 & 1804 & 8 & 27.1 & 1.0 & 23.8 & 1.4 & 8.82 & 0.35 & 15.4 & 0.4 & 3.03 & 0.06 & 40 \\
8 & 2044 & 37 & 17.6 & 0.6 & 13.7 & 1.1 & 3.84 & 0.54 & 19.5 & 0.3 & 4.04 & 0.05 & 60 \\
9 & 1933 & 37 & 20.9 & 0.9 & 18.3 & 0.6 & 6.06 & 0.77 & 18.2 & 0.5 & 3.25 & 0.09 & 50 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Test results of pervious concrete (PC) properties.  
Figure 2: Freeze-thaw cycles test: (**a**) laboratory test; (**b**) specimen with cracks after freeze-thaw cycles.  
and K values, the primary and secondary order of the influence factors is porosity, water-binder ratio, and aggregate size. The optimal combination is porosity 25%, W/B 0.25, and aggregate size 13.2-16.0 mm. Figure 3d shows the influence of various factors on freeze-thaw cycles. Based on R and K values, the primary and secondary order of the influence factors is aggregate size, porosity, and water-binder ratio. The optimal combination is aggregate size 4.75-9.5 mm, porosity 15%, and W/B 0.35.