# Experimental Study of Low Temperature Performance of Porous Asphalt Mixture
## 2 Low Temperature Performance Test
### Design of Mix Proportion  
In the current experimental programme, the gradation design method based on Bailey method was adopted [51; 52], and the gradation design process is illustrated in Figure 3. At the outset, to conduct the gradation design of porous asphalt mixture using Bailey method, the parameters including the 0.075 mm sieve passing percentage, design density, volume ratio of coarse aggregate, and reserved porosity need to be determined. The reasonable gradation obtained based on Bailey method is listed in Table 9. The bitumen/aggregate ratio was 5.36%, the porosity was 20.55%, and the Marshall stability was 4920 N. In the gradation design, two types of coarse aggregates (denoted as CA-1 and CA-2), one type of fine aggregate (denoted as FA) and one type of filler (denoted as MF) were used. The percentage by mass passing through 0.075 mm sieve aperture was 5% and the design density was 103% of the loose density. The volume ratio of coarse aggregate (CA-1:CA-2) was determined to be 55:45 according to the requirements in JTG F40-2004 [50]. The reserved porosity was determined to be 25% according to the requirement of the target porosity. Figure 3: Gradation design of porous asphalt mixture based on Bailey method. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test Item** & **Unit** & **Matrix asphalt/SINOTPS = 88/12** \\ \hline Needle penetration (25 \({}^{\circ}\)C, 100 g, 5 s) & 0.1 & 49.5 \\ Softening point (ring and ball method) & \({}^{\circ}\)C & 93.9 \\ Ductility (5 \({}^{\circ}\)C) & cm & 45.3 \\ Elastic restitution & \% & 96.8 \\ Dynamic viscosity (60 \({}^{\circ}\)C) & Pa-s & 69,618 \\ Viscosity (135 \({}^{\circ}\)C) & Pa-s & 2.883 \\ Viscous toughness & N-m & 23.47 \\ Toughness & N-m & 15.57 \\ Quality change & \% & 0.07 \\ Rolling thin film & Residual needle & \% & 76.2 \\ oven heated & penetration ratio & \% & 29.1 \\ (RTFOT) & Residual ductility (5 \({}^{\circ}\)C) & cm & 29.1 \\ \hline \hline \end{tabular} Note: Tests were carried out according to Chinese Standard JTG E20-2011 [49].  
\end{table} 
Table 8: Technical indicators of modified asphalt (12% SINOTPS). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Bitumen/Aggregate Ratio (\%)**} & \multicolumn{4}{c}{**Percentage of Mineral Aggregate (\%)**} \\ \cline{2-5}  & S10 & S12 & S16 & Limestone powder \\ \hline
5.36 & 46.68 & 37.02 & 12.83 & 3.47 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Mineral aggregate composition of gradation scheme. Because of porous asphalt is an open-graded mixture, its optimal bulk density, Marshall stability and flow are not directly comparable with dense graded asphalt. Therefore, it is not viable to determine the optimum asphalt content of porous asphalt mixture directly by using Marshall test method. Instead, the desirable range of asphalt content for porous asphalt mixture should be first determined by employing the binder drainage test and Cantabro test, and then the optimum asphalt content can be determined with respect to the functional requirements of porous pavement. The binder drainage test measures the mass of binder leakage from asphalt mixture through the perforated metal basket [53], and it determines the upper bound of bitumen/aggregate ratio. The Cantabro test measures the mass of disintegration from asphalt mixture under the effect of simulated traffic load in the Los Angeles machine [54], and it determines the lower bound of bitumen/aggregate ratio. Reference is made to Table 9 of the mineral aggregate composition of porous asphalt mixture as the starting point. Assuming the initial bitumen/aggregate ratio as 5.36%, five different bitumen/aggregate ratios were taken in the proximity of the initial bitumen/aggregate ratio as tabulated in Table 10, where the bitumen/aggregate ratio ranged from 3.6% to 5.6% with equal increment of 0.5%.