# Experimental Study of Low Temperature Performance of Porous Asphalt Mixture
## 2 Low Temperature Performance Test
### Orthogonal Experimental Design  
Orthogonal experimental design [55] is a commonly used scientific method for designing multi-factor experiments. It uses a set of standardized orthogonal tables to arrange experiments, and the technique has been widely adopted in the planning and design of experimental trials in production engineering and quality control [56]. In the implementation, the combinations of different experimental factors and levels are evenly matched and rationally divided. The experimental results are processed by statistical methods and as a result scientific conclusions can be obtained. The main advantage of orthogonal experimental design is to enable the selection of representative combinations of experimental factors instead of exhausting all possible combinations. Through the analysis of some representative experimental results, the influence degree of different factors on each evaluation indicator can be obtained, and the best combination of multiple factors can be obtained to achieve the experimentation purpose. In this study, the choice of factors in the orthogonal experimental design was based on the environmental conditions and the representative mix designs. Four factors, namely the porosity (in %), modifier content (in %), aging, and test temperature (in \({}^{\circ}\)C), were included. For each factor, three levels were considered. The resulting matrix can cover a wide range of design scenarios of porous asphalt mixture in low temperature conditions. (1) Orthogonal table design  
The mineral aggregate gradation and optimum asphalt content of porous asphalt mixture obtained in Section 2.2 were used in the test. The types and properties of raw materials have been described in detail in Section 2.1. Based on the above discussions, the selected levels of modifier content and porosity are presented in Table 12, henceforth, a four-factor three-level orthogonal table as tabulated in Table 13 is set up. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Test Item** & **Unit** & **Test Result** & \begin{tabular}{c} **Indicator** \\ **Requirement** \\ \end{tabular} \\ \hline \multirow{3}{*}{Marshall test} & Porosity & \% & 20.7 & 18–22 \\  & Marshall stability (double-sided compaction 50 times) & N & 5480 & \(\geq\)5000 \\  & Flow value & mm & 2.38 & 2–4 \\ \hline \multirow{2}{*}{\begin{tabular}{c} Water \\ permeability \\ \end{tabular} } & Water permeability & mL/15 s & 1602 & \(>\)800 \\  & coefficient & & & \\ \hline \multirow{2}{*}{\
\begin{tabular}{c} High \\ temperature \\ stability \\ \end{tabular} } & Dynamic stability (60 \({}^{\circ}\)C, 0.7 MPa) & times/mm & 5458 & \(\geq\)5000 \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Water \\ immersion \\ stability \\ \end{tabular} } & Residual stability of & \% & 94.0 & \(\geq\)85 \\  & water immersion & \% & 2.49 & \(\leq\)15 \\  & Freeze-thaw splitting & \% & 91.4 & \(\geq\)80 \\  & strength ratio & \% & \multicolumn{1}{c}{} & \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Performance verification of porous asphalt mixture. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Factor**} \\ \cline{2-5}
**Level Number** & A & B & C & D \\  & Porosity & Modifier content & Aging & Test temperature \\ \hline
1 & 16.2\% & 9\% & No aging & 0 \({}^{\circ}\)C \\
2 & 20.7\% & 12\% & Short-term aging & \(-\)10 \({}^{\circ}\)C \\
3 & 23.8\% & 15\% & Long-term aging & \(-\)20 \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Values of levels of each factor. To simulate the aging of porous asphalt mixture from construction process to service stage, the aging of porous asphalt mixture was divided into short-term and long-term aging levels. Short-term aging refers to the aging of porous asphalt mixture caused by temperature during the paving construction process from mixing plant to pavement compaction. Long-term aging refers to the aging caused by external environmental factors including air, sunlight, precipitation, and traffic loads during the service of porous asphalt pavement.