*3.3. FTIR–ATR Spectrometry*

The results for the FTIR–ATR analysis are presented in Figures 8–10. Asphalt aging was characterized by oxidization indices shown in Table 1. The C=O and S=O indices both increased significantly with RAP and blended bitumen relative to the virgin bitumen. There was a small increase in the RAP bitumen compared to the blended bitumen in the indices. The aging indices were higher for the fine RAP, likely because of its higher surface area, compared to the course RAP, which allowed for a greater degree of aging. The sulfoxide indices for all bitumen were higher, as was typical for asphalt bitumen [30].

**Figure 7.** Reduced G\* for CR and FR at 10 ◦C.

**Figure 8.** Compilation of FTIR spectra featuring C=O and S=O oxidation bands.

**Figure 9.** FTIR carbonyl oxidation indices.

**Figure 10.** FTIR sulfoxide oxidation indices.

#### *3.4. Environmental Scanning Electron Microscopy (ESEM) Analysis*

The images from the ESEM analysis are shown in Figure 11, before electron beam irradiation and after stabilization of the sample. The bitumen before irradiation showed a 'bee' type structure, similar to the one found in AFM observations [31,32], which was denser in the RAP bitumen compared to the virgin and blended bitumen.

**Figure 11.** Environmental scanning electron microscopy (ESEM) Images of Samples at 1000× before Electron Beam Irradiation and After Image Stabilized.

After the sample was exposed to the electron beam, and the accumulation of energy irradiated the sample, the asphalt bitumen tended to reveal a 'fibril' microstructure as lighter components of the bitumen dispersed [33], which was the case for the virgin bitumen. However, both the blended and RAP bitumen responded much less to beam irradiation. This was likely because the microstructure of the bitumen stiffened from aging, and the molecular mobility was reduced. This made revealing the microstructure by ESEM irradiation a slower and more difficult process with the settings that were used.
