## 3 Experimental Design of Composite-Modified Asphal
### Materials
#### 3.1.2 Rock Asphalt  
Rock asphalt is a substance formed by complex physical and chemical changes in nature, as crude oil-like material constantly rises to the surface due to crustal movement and fractures. It has a vein-like structure intermixed with various rocks and minerals, predominantly black-brown granular in nature. Additionally, it contains very fine limestone particles and emits a slightly kerosene-like odor. This mineral formation occurs within mountains and rock fissures, requiring the ability to withstand high pressure. The polymerization degree is high, as well as the molecular weight, resulting in a high softening point. Rock asphalt exhibits high-temperature and weathering resistance, as well as a high nitrogen content and absence of wax; consequently, it possesses strong resistance to rutting, water damage, and aging while also enhancing the quality of wax-containing asphalt. Currently, the predominant sources of natural asphalt in the world are Albanian rock asphalt (ARA), Buton rock asphalt (BRA), Iranian rock asphalt (YRA), Qingchuan rock asphalt (QRA), and North American rock asphalt (AG). The technical properties of these five types of natural asphalts were tested according to \"Asphalt mixture modification additives Part 5: natural asphalt\" [24], and the results are presented in Table 2. From Table 2, it is evident that Buton rock asphalt (BRA) exhibits a higher ash content and coarser particle size distribution compared to the other four types of rock asphalt, making it unsuitable for wet modification. In contrast, Qingchuan rock asphalt (QRA) has a higher asphalt content and finer particle size distribution, which allows for optimal blending with mastic asphalt at lower proportions to achieve superior compounding effects. To further investigate the modification effect and compatibility of different types of rock asphalt on petroleum asphalt, 70# asphalt was selected as the base material. Five types of rock asphalt were blended with a ratio of 10% to the base material to prepare a modified mixture. According to the test procedure for waterproof materials in highway engineering [23], penetration, ductility, softening point, and other indicators were analyzed for the five modified mixtures. The results are presented in Table 3. It is evident from the table that various rock bitumen-modified asphalts exhibit distinct degrees of reduction in penetration and ductility, indicating the influence of rock bitumen on enhancing viscosity and improving the low-temperature properties of asphalt. The softening points of the modified asphalts were all enhanced, and rock asphalt had a positive impact on the high-temperature performance of asphalt. Among them, QRA-modified asphalt exhibited the most significant improvement in softening point, with only minimal reduction in penetration and ductility compared to other modified asphalts. After considering various \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Result** & **Requirement** \\ \hline Penetration (100 g, 5 s, 25 \({}^{\circ}\)C, 0.1 mm) & 68 & 60–80 \\ \hline Penetration Index PI & \(-\)1.0 & \(-\)1.5\(+\)1.0 \\ \hline Softening Point (\({}^{\circ}\)C) & 49 & \(\geq\)46 \\ \hline Kinematic Viscosity (60 \({}^{\circ}\)C, Pa-s) & 220 & \(\geq\)180 \\ \hline \multirow{2}{*}{Ductility} & (10 \({}^{\circ}\)C, cm) & 40 & \(\geq\)25 \\ \cline{2-3}  & (15 \({}^{\circ}\)C, cm) & \(>\)150 & \(\geq\)100 \\ \hline Solubility in Trichlorethylene (\%) & 99.87 & \(\geq\)99.5 \\ \hline Density (15 \({}^{\circ}\)C, g/cm\({}^{3}\)) & 1.033 & Measured Value \\ \hline Quality Change (\%) & \(-\)0.334 & \(\leq\)\(\pm\)0.8 \\ \hline \multirow{2}{*}{After TFOT (163 \({}^{\circ}\)C, 5 h)} & Penetration Ratio & \multirow{2}{*}{63} & \multirow{2}{*}{\(\geq\)61} \\  & (25 \({}^{\circ}\)C, \%) & & \\ \cline{2-3}  & Residual Ductility & & \\ \cline{2-3}  & (10 \({}^{\circ}\)C, cm) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Technical parameters of 70# asphalt.