# Laboratory Evaluation of Eco-Friendly Pervious Concrete Pavement Material Containing Silica Fume
## 2 Materials and Methods
### Testing Methods  
Porosity is a characteristic of pervious concrete, and it is directly related to permeability. The effective porosities (proportion of open pore and semi-open pore) of all mixtures were tested. The effective porosity was characterized by the average of three specimens and determined using the equation,  
\[P=(1-\frac{m_{1}-m_{0}}{V\rho})\times 100\% \tag{1}\]  
where \(m_{0}\) is the mass of the specimen submerged in water (g); \(m_{1}\) is the saturated surface-dry mass of the specimen (g); \(\rho\) is the water density (g/cm\({}^{3}\)), and \(V\) is the volume of the specimen (cm\({}^{3}\)). Permeability is the most important property of pervious concrete. According to the Chinese national standard CJJ/T 135-2009 [34], the constant head permeability test was adopted and the homemade instrument was used to measure the permeability coefficient. Detailed description of the permeability instrument is shown in Figure 3. A detailed description of the test procedure could be found elsewhere [33]. In every group, the permeability was characterized by the average permeability coefficients of three specimens. The permeability coefficient can be calculated by the following equation according to the Chinese national standard [34]:  
\[k=\frac{QL}{AHt} \tag{2}\]  
where \(k\) is the permeability coefficient of the specimen at 20 \({}^{\circ}\)C (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.  
Figure 2: Specim preparation procedure. \begin{table}
\begin{tabular}{p{85.4 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Test** & **Number of Specimens in Each Group** & **Test Condition/Set-Up** \\ \hline Porosity & 3 cubic specimens & The porosity, permeability and compressive strength tests can adopt 3 same specimens and the test sequence is: porosity, permeability, compressive strength. Test temperature: 20 \(\pm\) 2 \({}^{\circ}\)C. \\ \hline Flexural strength & 3 prismatic specimens & Test temperature: 20 \(\pm\) 2 \({}^{\circ}\)C. \\ \hline Freeze-thaw cycle & 12 cubic specimens (4 freeze-thaw levels, 3 for each level). & Highest temperature: 5 \({}^{\circ}\)C, lowest temperature: \(-\)18 \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The experimental programme. Compressive strength and flexural strength tests were conducted in accordance with the Chinese national standard GB/T 50081-2002 [35]. The compressive strength test was conducted with a hydraulic pressure testing machine, and the flexural strength was conducted with a closed-loop, servo-controlled hydraulic testing system. The loading rates for compressive strength and flexural strength were 5 kN/s and 0.05 kN/s, respectively. The third-point bending test, shown in Figure 4, was adopted to determine the flexural strength. In each group, three specimens were tested and the average compressive and flexural strengths were calculated to characterize the strength property. The compressive and flexural strengths can be calculated by following equations:  
\[f_{c}=\frac{F}{A} \tag{3}\]  
\[f_{f}=\frac{3}{2}\frac{FL}{bh^{2}} \tag{4}\]  
where \(f_{c}\) is the compressive strength of the specimen (MPa); \(f_{f}\) is the flexural strength of the specimen (MPa); \(A\) is the pressure-bearing surface area of the specimen; \(F\) is the failure load (N); \(L\) is the distance between two supporting points (mm), \(L\) = 300 mm; \(b\) is the section width of the specimen (mm), \(b\) = 100 mm; \(h\) is height of the specimen (mm), \(h\) = 100 mm. The fast freezing method was adopted to conduct a freeze-thaw cycles test according to the Chinese standard GB/T 50082-2009 [36]. Levels of the freeze-thaw cycles were set to 25, 50, 75,  
Figure 4: Flexural strength test. Figure 3: Homemade permeability measure instrument. and 100 cycles. In each freeze-thaw cycles level, three cubic specimens were used.