## 2 Materials and Methods
### Sample Preparation  
In this study, the heat fusion method and shearing method were selected to produce asphalt rubber (to illustrate performance differences) using an X-blade mixer and a high-speed shear. Auxiliary equipment included temperature control heaters, mixing pots, electronic scales, thermometers and glass rods. The steps of preparation are as follows and the preparation process is shown in Figure 2.  
The samples for the shearing method were prepared as follows:  
(1) The matrix asphalt was placed in an oven, the temperature was set to 150 \({}^{\circ}\)C and the asphalt was removed after heating to a fully liquefied state.  
(2) The rubber particle was heated and dried in a small oven at 110 \({}^{\circ}\)C. Worth noting that if the temperature is too low, the moisture in the rubber powder cannot be easily removed, and if the temperature is too high, the space network of the rubber powder will be destroyed and affect the properties of AR.  
(3) The mixer was set to a speed of 300 r/min the mixer was operated until the temperature rose to 150 \({}^{\circ}\)C to stir the asphalt.  
(4) The rubber particle was added during the stirring process slowly and stirred at 170-180 \({}^{\circ}\)C continuously for 30 min to prevent asphalt aging caused by overheating.  
(5) After the completion of the stirring, the sample was placed on a shearing machine and subjected to high speed shearing at a speed of 4000 r/min, the shearing time was 1 h and the shearing temperature was controlled in the range of 170-180 \({}^{\circ}\)C.  
(6) After the completion of the shearing, the sample was taken out and stirred for 1 h (reaction time), and the sample was stirred at 170 \({}^{\circ}\)C for 1 h.  
The heat fusion method was to directly put the rubber powder into the reaction tank under the same process parameters, and to produce it only by stirring.  
After completion, it was poured into a test container for the follow-up experiments for both methods.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Index** & **ZB-01** & **HMD-1** & **HMD-2** \\ \hline \multirow{4}{*}{Appearance} & Grayish Black or & Yellow Black or & Yellow Black or \\  & Yellowish Solid Fine & Yellowish Solid Fine & Yellowish Solid Fine \\  & Powder & Powder & Powder \\ Active ingredient content (\%) & \(\geq\)95 & \(\geq\)95 & \(\geq\)95 \\ Apparent density (g/cm\({}^{3}\)) & 0.9–1.2 & 0.6–0.8 & 0.5–0.7 \\ Melting point (\({}^{\circ}\)C) & \(\geq\)110 & \(\geq\)90 & \(\geq\)110 \\ Fineness (80 mesh sieve & \(\leq\)2 & \(\leq\)2 & \(\leq\)2 \\ residue) (\%) & \(\leq\)0.5 & \(\leq\)0.5 & \(\leq\)0.5 \\ Add amount (\%) & 1–3 & 2–5 & 2–5 \\ Add temperature (\({}^{\circ}\)C) & 185–195 & 180–190 & 185–195 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Parameters of different stabilizers.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test Items** & **Ash** & **Acetone** & **Carbon Black** & **Rubber Hydrocarbon** \\  & **Content (\%)** & **Extract (\%)** & **Content (\%)** & **Content (\%)** \\ \hline Measured value & 7 & 7 & 28 & 55 \\ Standard Value & \(\leq\)8 & \(\leq\)22 & \(\geq\)28 & \(\geq\)42 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Chemical properties of crumb rubber.