# Recycling Aged Asphalt Using Hard Asphalt Binder for Hot-Mixing Recycled Asphalt Mixture
## 3 Results and Discussion
### Performance of Hard Asphalt Modified Aged Asphalt
#### 3.1.2 FTIR Spectra Analysis of Recycled Asphalt Binder  
Figure 6a presents the FTIR spectra of virgin asphalt (VA) and aged virgin asphalt. In Figure 6, a frequency band present at 3800-3500 cm\({}^{-1}\) is caused by the vibration of bound water or free water and CO\({}_{2}\) in ambient air; the strong peaks around 2922-2852 cm\({}^{-1}\) are associated with the stretching vibrations in the aliphatic chain of the asphalt binder [23]; the peak at 1600 cm\({}^{-1}\) denotes to the vibration of C=C in the benzene skeleton; the peak at 1462 and 1376 cm\({}^{-1}\) relates to the deformation vibrations of the aliphatic chain; the peak at 1031 cm\({}^{-1}\) is the stretching vibrations of the sulfoxide group (S=O); the peaks at 863, 811, and 747 cm\({}^{-1}\) are resulting from the bending vibration of C-H in the aromatic ring. The aging level of asphalt binder samples can be determined by comparing the absorbance of the functional group. The significant difference between three samples is that the transmittance of the functional group of C=C, C=O, and S=O increased after the virgin asphalt binders were aged, and a greater aging level leads to a higher absorbance of those functional groups. The increase in C=O indicates that the oxygen-containing functional groups such as aldehydes, ketones, esters, and carboxylic acids are formed during the aging process of the asphalt binder. Furthermore, the increase in S=O demonstrates that the sulfur element reacts with oxygen to form a polar functional sulfoxide group.  
Figure 5: Test results of the EME-20 asphalt mixture containing 50% of RAP under 0–25 Hz.  
Figure 6: _Cont_.  
Figure 6b illustrates the FTIR spectra of virgin asphalt (VA), Trinidad lake asphalt (TLA), and hard asphalt produced with 60% of VA and 40% of TLA. By comparing the FTIR spectra of VA and TLA, most of the transmittance peaks of TLA are near the absorption peaks of the matrix asphalt. The only new absorption peaks appear at 535, 467, and 428 cm\({}^{-1}\), which correspond to naphthalene functional groups. The addition of a naphthalene functional group is helpful for enhancing the structural strength of petroleum asphalt molecules, which will increase the viscosity of asphalt and enhance the cohesion of asphalt binder and the adhesion with aggregate. In addition, the transmittance peak area of sulfoxide group S=O at 1031 cm\({}^{-1}\) of TLA is significantly larger than that of ordinary asphalt binder. The TLA was intensively exposed in an open-air environment, which accelerated the oxidation of TLA. The sulfur and oxygen have sufficient chemical reaction to form more sulfoxide groups. Furthermore, HA and TLA have the same characteristic peaks, in which the transmittance of each functional group in HA is smaller than that of TLA. The above results show that the addition of TLA only changes the proportion of each component in VA, and there is no chemical reaction in this process.  
One of the objectives of this work is to rejuvenate the aged asphalt binder using HA containing TLA for producing a high-modulus recycled mixture with high RAP content. Thus, blended asphalt binder samples containing 50% aged asphalt (A12h, A26h) and 50% HA were prepared. Their FTIR spectra are shown in Figure 6c,d. From the effect of HA on aged asphalt, it can be concluded that the sulfoxide group S=O peaks at 1031 cm\({}^{-1}\) in both A12h + HA and A26h + HA are sharper compared to that in aged asphalt. This is because the sulfoxide group tends to disintegrate under high temperatures. Furthermore, the appearance of peaks at 535, 467, and 428 cm\({}^{-1}\) in both A12h+HA and A26h+HA indicates that the naphthalene functional group in TLA was introduced in the rejuvenated asphalt binder.