3.3.2. Molecular Weight Distribution

Figure 11 shows the relative molecular mass (*M*n) distribution structure of the 70# matrix asphalt and the regenerated asphalt. The horizontal coordinate is the logarithm of the heavy average molecular weight, and the vertical coordinate is the relative content of asphalt. From Figure 11, we can see that the molecular weight of asphalt was mainly in the range of 102–104 and the molecular weight distribution of asphalt after aging showed a shoulder peak in the range of 103.5–104.5. The relative content increased, which indicated that the aging of asphalt promoted the increase of the macromolecular content. At the same time, the macromolecular content of asphalt decreased after the addition of the regeneration agent. The shoulder in the range of 103.5–104.5 slowly became slower with the increase of the regeneration agent dose. The correlation study concluded a correlation between the molecular weight size of asphalt and asphalt properties. The more the macromolecular size in asphalt, the worse the asphalt performance [23]. The results of Jenning [23] and Kim [24] averaged the GPC data into 13 intervals with a sizeable molecular size (LMSs; intervals 1–5), a medium molecular size (MMSs; intervals 6–9), and a small molecular size (SMSs; intervals 10–13). Figure 11 shows the molecular size distributions of the asphalt specimens. As seen in Figure 12, the increase in the rejuvenation agent admixture and the regenerated asphalt exhibited higher MMSs and reduced LMSs. This is consistent with the GPC results, where adding a rejuvenation agent resulted in lower *M*<sup>w</sup> and PD values. The LMSs of asphalt showed a better correlation with the asphalt properties than other dimensions [23]. Therefore, the study on the regeneration agent effect focused on LMSs, showing that LMSs significantly decreased when the regeneration agent dose was 6%, which coincided with the lower *M*<sup>w</sup> and PD values found in the GPC test. It indicated that the regenerating agent could significantly reduce the asphalt macromolecular size. Although rejuvenation agents could replenish the components lost by asphalt due to aging, it was not easy to rebalance the distribution of regulated molecules. The GPC test results showed that the rejuvenator could reduce the size of large and medium molecules and increase the size of small molecules; the rejuvenator had the effect of decomposing the large and medium molecules in asphalt. At the same time, the proportion of heavy components in the asphalt was reduced, and the proportion of light components was increased after the incorporation of regenerants. This inevitably weakened the high temperature performance and the Brinell viscosity of the aged asphalt. However, whether the ratio of each component in the recycled asphalt is the same as that of the original asphalt needs further study and analysis.

**Figure 11.** Chromatograms of the original asphalt and the regenerated asphalt.

**Figure 12.** Molecular size distributions of the asphalt specimens.
