## 2 Influential Factors on the Performance of GSP
### Raw Materials and Admixtures
#### 2.2.2. Asphalt Binder  
The types of asphalt binder in OMA include base asphalt, rubber asphalt, SBS-modified asphalt, and high-viscosity modified asphalt. Due to various characteristics at different temperatures, the optimal type and content of asphalt binder as two factors varies in OMA design, as shown in Table 5. Orthogonal experiment uncovers the effects of binder on the relative OMA or GSP sample, as illustrated in Tables 5 and 6. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Author**} & \multirow{2}{*}{**Binder Types**} & \multirow{2}{*}{**Void Rate**} & **Optimum** & **Unconfined** & \multirow{2}{*}{**Marshall**} & **Cantabro Loss** \\  & & **[\%]** & **Asphalt** & **Compressive** & **Strength [kPa]** & **Stability [kN]** & **[\%]** \\ \hline \multirow{4}{*}{Setyawan} & 50-pen straight run & \multirow{2}{*}{27.44} & \multirow{2}{*}{4} & \multirow{2}{*}{1691.59} & \multirow{2}{*}{N/A} & \multirow{2}{*}{18.7} \\  & asphalt & & & & & \\ \cline{1-1} \cline{5-6}  & 7\%SBS asphalt & & & & & \\ \cline{1-1} \cline{5-6}  & 100-pen straight & \multirow{2}{*}{27.74} & \multirow{2}{*}{4} & \multirow{2}{*}{760.64} & \multirow{2}{*}{N/A} & \multirow{2}{*}{34.3} \\  & run asphalt & & & & & \\ \hline [PERSON] et al. [48] & Rubber-asphalt & 22.1 & 3.6 & N/A & 6.80 & 23.8 \\ \hline \multirow{4}{*}{[PERSON] et al. [54]} & High-viscosity asphalt & \multirow{2}{*}{26.0} & \multirow{2}{*}{3} & \multirow{2}{*}{N/A} & \multirow{2}{*}{3.6} & \multirow{2}{*}{19.5} \\  & asphalt & & & & & \\ \cline{1-1} \cline{5-6}  & Rubber-asphalt & 26.2 & 3 & N/A & 2.7 & 38.4 \\ \cline{1-1} \cline{5-6}  & SBS asphalt & 25.9 & 3 & N/A & 3.0 & 32.5 \\ \cline{1-1} \cline{5-6}  & Ordinary asphalt & 25.8 & 3 & N/A & 2.4 & 48 \\ \hline [PERSON] et al. [55] & 4.4\%SBS asphalt & 25 & 4.4 & N/A & 4.6 & N/A \\ \hline [PERSON] et al. [56] & SBS asphalt & 22.47 & 3.4 & N/A & 4.15 & 14.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Optimal binder and high-temperature performance of OMA. Asphalt binder with high viscosity and low penetration, such as 50-pen straight-run asphalt, SBS asphalt, rubber-asphalt, and high-viscosity asphalt, can increase strength and reduce Cantabro loss for OMA which will result in good high-temperature performance of GSP. However, binder types have little impact on void space structure in OMA, as well as strength and moisture resistance of GSP [46; 54]. OMA samples using SBS asphalt as binder can obtain favorable water permeability. [PERSON] et al., explained that modified asphalt protected OMA from drainage that caused void-blocking [46]. Therefore, the performance of following GSP samples was also enhanced, especially in low-temperature cracking resistance [46; 54; 55]. Rubber asphalt also promotes high-temperature performance of GSP. It is considered as a potential candidate due to its excellent cost-effectiveness and environment-friendliness [48].,High-viscosity asphalt also shows advantages of flexural tensile strain and stiffness modulus at a low temperature, which is associated with better anti-cracking performance [54]. Optimal binder content of OMA can be determined by three main parameters in orthogonal testing: compressive strength, tensile strength, and Cantabro loss. The value of it mostly falls in a range of 3%-5%, due to different test methods. However, it can be argued that a high content rate of binder in OMA can increase toughness of OMA, leading to good anti-cracking performance of GSP [57], because the Marshall stability of OMA continues to rise with the increase of the binder content rate, even up to 9% [58]. Besides these two factors: binder type and content in OMA, bonding force for the asphalt-cement interface is overlooked in steps of influential factors analysis, which can contribute to low-temperature performance of GSP.