## 2 Materials  
### Materials  
The properties of asphalt binders were measured according to the test methods of specification, the Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering (JTG E20-2011) [28]. AH-70 (penetration grade) base asphalt was used as the binder in this work, and its main technical indicators are summarized in Table 1. The Buton rock asphalt (BRA, Figure 1) that was used in this test had been sifted with an 0.15-mm sieve. The technical indicators of BRA are shown in Table 2. Two kinds of low-temperature modifiers, styrene-butadiene rubber (SBR, Figure 1) and nano-CaCO\({}_{3}\) (Figure 1), were adopted in this test. Their main technical properties are presented in Tables 3 and 4, respectively.  
Figure 1: Materials: (**a**) Buton rock asphalt (BRA); (**b**) styrene–butadiene rubber (SBR); (**c**) Nano-CaCO\({}_{3}\).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test Items** & **Industry Standard** & **Test Results** & **Test Methods [28]** \\ \hline Penetration at 25 \({}^{\circ}\)C (0.1 mm) & 60 & 75.2 & T 0604-2000 \\ Penetration Index & \(-\)2\(\cdot\)2 & 0.968 & T 0604-2000 \\ Softening point (\({}^{\circ}\)C) & \(\geq\)100 & 51.5 & T 0606-2000 \\ Ductility at 15 \({}^{\circ}\)C (cm) & \(\geq\)46 & \(>\)150 & T 0605-1993 \\ Rotation viscosity/135 \({}^{\circ}\)C (Pa-s) & \(\backslash\) & 0.451 & T 0615-2000 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Technical properties of base asphalt binder AH-70.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Test Items** & **Industry Standard** & **Test Results** & **Test Methods** \\ \hline Volatile matter content (\%) & \(\leq\)0.60 & 0.30 & GB/T 6737 \\ \hline Ash content (\%) & \(\leq\)0.50 & 0.10 & GB/T 4498 \\ \hline Organic acids content (\%) & 4.50–6.75 & 6.15 & GB/T 8657 \\ \hline Soap content (\%) & \(\leq\)0.50 & 0.01 & GB/T 8658 \\ \hline Bound styrene content (\%) & 22.5–24.5 & 23.7 & GB/T 8658 \\ \hline Raw rubber Mooney viscosity [50 ML(1 + 4)100 \({}^{\circ}\)C] & 45–55 & 52 & GB/T1232.1 \\ \hline Compound rubber Mooney viscosity [50 ML(1 + 4)100 \({}^{\circ}\)C] & \(\leq\)93 & 70 & \\ \hline Tensile strength (MPa) & \(\geq\)25.5 & 25.8 & \\ \hline Tensile elongation (\%) & \(\geq\)340 & 412 & GB/T 8656 A \\ \hline
300\% fixed elongation stress at 145 \({}^{\circ}\)C (MPa) & 25 min & 17.7 \(\pm\) 2.0 & 16.6 \\ \hline
50 min & 20.6 \(\pm\) 2.0 & 20.8 & \\ \hline
50 min & 21.5 \(\pm\) 2.0 & 21.6 & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Technical properties of SBR.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test Items** & **Test Results** & **Test Methods [30]** \\ \hline Appearance & White powder & \\ Nano-CaCO\({}_{3}\) content (\%) & \(\geq\)98 & \\ PH value & 8.0–10.5 & \\ Whiteness (\%) & \(\geq\)95 & \\ Activation rate (\%) & \(\geq\)98 & \\ Volatile matter content at 105 \({}^{\circ}\)C (\%) & \(\leq\)0.5 & GB/T19590-2011 \\ Insoluble matter content in hydrochloric acid (\%) & \(\leq\)0.03 & GB/T19590-2011 \\ Passing rate for 45-\(\upmu\) experimental sieve (\%) & \(\leq\)0.02 & \\ Oil absorption value (\%) & \(\leq\)35 & \\ \hline Insoluble matter content in hydrochloric acid (\%) & \(\leq\)0.03 & \\ Passing rate for 45-\(\upmu\) experimental sieve (\%) & \(\leq\)0.02 & \\ Oil absorption value (\%) & \(\leq\)35 & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Technical properties of nano-CaCO\({}_{3}\).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test Items** & **Industry Standard** & **Test Results** & **Test Methods [29]** \\ \hline Penetration at 25 \({}^{\circ}\)C (0.1 mm) & 60 & 75.2 & T 0604-2000 \\ Penetration Index & \(-\)2\(\cdot\)2 & 0.968 & T 0604-2000 \\ Softening point (\({}^{\circ}\)C) & \(\geq\)100 & 51.5 & T 0606-2000 \\ Ductility at 15 \({}^{\circ}\)C (cm) & \(\geq\)46 & \(>\)150 & T 0605-1993 \\ Rotation viscosity/135 \({}^{\circ}\)C (Pa-s) & \(\backslash\) & 0.451 & T 0615-2000 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Technical properties of base asphalt binder AH-70.