# Impact of Preheating Temperatures and RAP Characteristics on the Activation of RAP Binder
## 3 Materials and Methods
### Methods
#### 3.2.1 Producing RAP-Art with Different Degrees of Aging  
\(\bullet\) Accelerated aging procedure  
The accelerated aging method was conducted on hot mixture asphalt (HMA) according to the standard (T 0734, 2000) [41] and recommendations provided by the NCHRP Report 871 [42]. First, the HMA was produced and cooled to room temperature in a loose state. Then, a short-term aging procedure (4 h, 135 \({}^{\circ}\)C) was conducted on loose HMA using an oven. The long-term aging procedure (5 days, 95 \({}^{\circ}\)C) was conducted on loose asphalt mixtures that had undergone the short-term aging procedure. The three kinds of loose asphalt mixtures (unaged, with short-term aging and with long-term aging) are regarded as artificial RAP with different levels of oxidation, prepared for the preheating and compaction procedure.  
\(\bullet\) RA binder recovery  
The 20-11100 asphalt mixture analyzer and R-215 rotary evaporator were used in this study to extract and recover the RA binder from RAP following the standard procedure (T 0722, 1993) [41] and (T 0727, 2011) [41]. Considering that a small amount of mineral powder still remains in the extract, a laboratory centrifuge was used to separate the mineral powder before the evaporation.  
\(\bullet\) Inspection of aging  
Before studying the influence of aging on the activation of RA binder, the oxidation levels of artificial RA binder need to be verified. In this study, the stiffness of artificial RA binder in different aging conditions was tested and compared using the dynamic shear rheometer (DSR) test. In addition, gel permeation chromatography (GPC) and Fourier-transform infrared spectroscopy (FTIR) tests were also conducted on SBS-modified binder. To verify the aging of artificial RA binder, six kinds of loose RAP-Art were prepared especially for asphalt tests given different aging conditions (i.e., unaged; aged at 135 \({}^{\circ}\)C for 4 h; aged at 95 \({}^{\circ}\)C for 1 day, 3 days or 5 days; and 8 days after short-term aging).  
\begin{table}
\begin{tabular}{l l l l l} \hline \hline \multirow{2}{*}{**Index**} & \multirow{2}{*}{**Unit**} & \multicolumn{3}{c}{**Test Results**} \\ \cline{3-5}  & & **RA-A** & **RA-B** & **RA-C** \\ \hline Softening point (Ring and Ball Test) & \({}^{\circ}\)C & 67.0 & 83.5 & 64.2 \\ Penetration (25 \({}^{\circ}\)C, 100 g, 5 s) & 0.1 mm & 30.0 & 21.1 & 26.6 \\ Ductility (15 \({}^{\circ}\)C, 5 cm/min) & cm & 8.0 & 0 & 12.3 \\ \hline \hline \end{tabular} RA-A, RA-B and RA-C are recovered from RAP-A, RAP-B and RAP-C, respectively.  
\end{table}
Table 1: Characteristics of RA binder.  
In the GPC tests, according to previous studies [43], the large molecular size (LMS) of RA binder shows an increase due to aging, and the percentage of LMS is usually used to indicate the aging of asphalt binder [44; 45]. In this study, the chromatogram was divided into 13 slices, and the first 5 slices of chromatogram were used to determine the percentage of LMS, reflecting the aging of RA binder.  
Based on the FTIR spectrum, the carbonyl (C=O) band occurring at the wavelength of 1695 cm\({}^{-1}\) and the saturated C-C vibration band at 1455 cm\({}^{-1}\) are commonly used to study the oxidation of asphalt binder [19; 44; 46]. During the oxidation process, the carbonyl (C=O) band grows, while the saturated C-C band remains relatively constant. In this study, the ratio of the area beneath the C=O and C-C peaks, called the aging index (AI), was used to compare the level of oxidation in asphalt binder under different aging conditions.