## 2 Materials and Research Content
### Materials
#### 2.1.3 Preparation of a New Type of Crumb Rubber (CRT)  
Since ordinary crumb rubber material has poor compatibility with asphalt, its elastic advantage is not fully exerted. Thus, its effect on road performance improvement is limited. CRT is a new rubber powder material made up of 40-mesh crumb rubber, TOR coupling agent, and some other materials. The advantage of this material is that it is developed through the dry process, which can solve the problems in the performance of the asphalt mixture due to the large content of CR. The properties of CRT and CR are listed in Table 4. The gradation of CRT is listed in Table 5. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Materials**} & \multirow{2}{*}{**Properties**} & \multirow{2}{*}{**Units**} & \multicolumn{2}{c}{**Specification**} & \multirow{2}{*}{**Test Results**} \\ \cline{3-4}  & & & & & **Limits** & & \\ \hline \multirow{4}{*}{CRT} & Relative density & g/cm\({}^{3}\) & — & 1.21 & \\  & Water content & \% & \textless{}1.0 & 0.53 & \\ \cline{1-1}  & Metal content & \% & \textless{}0.01 & 0.004 & \\ \cline{1-1}  & Fiber content & \% & \textless{}1.0 & 0.003 & \\ \hline \multirow{4}{*}{CR} & Relative density & g/cm\({}^{3}\) & 1.10–1.30 & 1.20 & \\ \cline{1-1}  & Water content & \% & \textless{}1.0 & 0.56 & \\ \cline{1-1}  & Metal content & \% & \textless{}0.05 & 0.016 & \\ \cline{1-1}  & Fiber content & \% & \textless{}1.0 & 0.0 & \\ \cline{1-1}  & Ash content & \% & \textless{}8 & 3.9 & \\ \cline{1-1}  & Acetone extract & \% & \textless{}22 & 14 & \\ \cline{1-1}  & Carbon black & \% & \textgreater{}28 & 40 & \\ \cline{1-1}  & content & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Performance of CRT and crumb rubber (CR). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Materials**} & \multirow{2}{*}{**Properties**} & \multirow{2}{*}{**Units**} & \multicolumn{2}{c}{**Specification Limits**} & \multirow{2}{*}{**Test Result**} \\ \cline{3-4}  & & & **Surface Layer** & & **Other Layers** \\ \hline \multirow{4}{*}{Coarse aggregate} & Stone crushing value & \% & \textgreater{}26 & \textgreater{}28 & 12.5 \\  & Los Angeles wear loss & \% & \textgreater{}28 & \textgreater{}30 & 16.0 \\  & Apparent relative density & \% & \textgreater{}2.60 & \textgreater{}2.50 & 2.8 \\  & Water absorption rate & \% & \textgreater{}2.0 & \textgreater{}3.0 & 0.90 \\ \cline{1-1}  & Rugged & \% & \textgreater{}12 & \textgreater{}12 & 6.0 \\ \cline{1-1}  & Needle-like particle & \textless{}15 & \textgreater{}18 & \\ \cline{1-1}  & content (mixture) & \% & \textgreater{}12 & \textgreater{}15 & 6.8 \\ \cline{1-1}  & Particle size greater than 9.5 mm & \textgreater{}18 & \textgreater{}20 & \\ \cline{1-1}  & Particle size less than 9.5 mm & \textgreater{}18 & \textgreater{}20 & \\ \cline{1-1}  & Particle content \textless{}0.075 mm through washing & \% & \textgreater{}1 & \textgreater{}1 & 4.2 \\ \cline{1-1}  & method & \% & \textgreater{}3 & \textgreater{}5 & 8.8 \\ \cline{1-1}  & Soft stone content & \% & \textgreater{}3 & \textgreater{}5 & 8.8 \\ \hline \multirow{4}{*}{Filler} & Apparent density & g/cm\({}^{3}\) & \textgreater{}2.5 & & 2.724 \\ \cline{1-1}  & Particle size range \textless{}0.6 mm & \textgreater{}100 & & 100 \\ \cline{1-1}  & \textless{}0.15 mm & \% & & 90–100 & 99.8 \\ \cline{1-1}  & \textless{}0.075 mm & & & 80–100 & 85.3 \\ \cline{1-1}  & Hydrophilic coefficient & — & \textless{}1 & 0.58 \\ \cline{1-1}  & Water content & \% & \textless{}1 & 0.1 \\ \cline{1-1}  & Plasticity index & — & \textless{}4 & 3.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Properties of coarse aggregate and filler.