# Experimental Study of Low Temperature Performance of Porous Asphalt Mixture
## 3 Experimental Method and Results
### Influence Analysis of Factors  
By analyzing the values of range in Table 15, the order of influence of factors on each of the evaluation indicators can be obtained. The order of influence of factors on the flexural tensile strength is as follows: modifier content > test temperature > aging > porosity. The order of influence of factors on the maximum bending strain is as follows: modifier content > test temperature > porosity > aging. The order of influence of factors on the bending stiffness modulus is as follows: modifier content > test temperature > aging > porosity. The influence of three levels of each factor on evaluation indicators is graphically represented in Figure 9. In the figure, A to D indicate the factor type as shown in Table 15, and 1 to 3 is the level number of each factor. (1) Porosity  
It can be seen from Figure 9 that the porosity has effect on the three low temperature performance evaluation indicators, but the effect is limited to within 4% over the range of porosity studied. When the porosity increased from 16.2% to 20.7%, the flexural tensile strength, maximum bending strain, and bending stiffness modulus of porous asphalt mixture decreased by 1.3%, 0.4%, and 3.5%, respectively. When the porosity further increased from 20.7% to 23.8%, the flexural tensile strength and bending stiffness modulus increased by 1.1% and 2.5% respectively, while the maximum bending strain decreased by 2.3%. Theoretically, an increase in porosity of asphalt mixture will reduce the flexural tensile strength. On the other hand, when the porosity is higher, the connected porosity also increases. The existence of interconnected pores could relieve the expansion pressure generated by the freezing action, and this could partially offset the adverse effect of porosity \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Group Number**} & \multicolumn{2}{c}{**Flexural Tensile Strength (MPa)**} & \multicolumn{2}{c}{**Maximum Bending Strain (\(\mu\epsilon\))**} & \multicolumn{2}{c}{**Bending Stiffness Modulus (MPa)**} \\ \hline
1 & 5.60 & 4996 & 1120 \\
2 & 5.26 & 5388 & 976 \\
3 & 5.15 & 5667 & 908 \\
4 & 5.57 & 4832 & 1153 \\
5 & 5.16 & 5491 & 939 \\
6 & 5.05 & 6257 & 807 \\
7 & 5.17 & 5220 & 991 \\
8 & 5.56 & 5063 & 1098 \\
9 & 5.22 & 5915 & 882 \\ \hline \hline \end{tabular}
\end{table} 
Table 14: Results of low temperature bending test. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Evaluation**} & \multirow{2}{*}{**Mean**} & \multicolumn{4}{c}{**Factor Type**} \\ \cline{3-5}  & & A & B & C & D \\
**Indicator** & & Porosity & Modifier & Aging & Test temperature \\ \hline \multirow{3}{*}{Flexural tensile strength (MPa)} & \(k_{1}\) & 5.33 & 5.45 & 5.40 & 5.20 \\  & \(k_{2}\) & 5.26 & 5.32 & 5.35 & 5.36 \\  & \(k_{3}\) & 5.32 & 5.14 & 5.16 & 5.46 \\  & Range & 0.07 & 0.31 & 0.24 & 0.26 \\ \hline \multirow{3}{*}{Maximum bending strain (\(\mu\epsilon\))} & \(k_{1}\) & 5550.33 & 5016.00 & 5438.67 & 5621.67 \\  & \(k_{2}\) & 5526.67 & 5314.00 & 5378.33 & 5467.33 \\ \cline{1-1}  & \(k_{3}\) & 5399.33 & 5946.33 & 5459.33 & 5187.33 \\ \cline{1-1}  & Range & 176.33 & 930.33 & 81.00 & 434.33 \\ \hline \multirow{3}{*}{Bending stiffness modulus (MPa)} & \(k_{1}\) & 1001.33 & 1088.00 & 1008.33 & 924.67 \\ \cline{1-1}  & \(k_{2}\) & 966.33 & 1004.33 & 1003.67 & 980.33 \\ \cline{1-1}  & \(k_{3}\) & 990.33 & 865.67 & 946.00 & 1053.00 \\ \cline{1-1}  & Range & 35.00 & 222.33 & 62.33 & 128.33 \\ \hline \hline \end{tabular}
\end{table} 
Table 15: Range analysis of results of low temperature bending test. on flexural tensile strength at low temperature. Through the analysis of orthogonal test results, it is found that among the three evaluation indicators, the maximum bending strain has the highest sensitivity to porosity. Therefore, it is advisable to design a single factor influence test to study the influence of porosity on the maximum bending strain, as described later in this paper.