# Study on the Aging Behavior of Asphalt Binder Exposed to Different Environmental Factors
## 3 Results
### Analysis of Outdoor Exposure on the Chemical Composition of Asphalt Binder  
#### 3.3.1 Effect of Outdoor Exposure on the Structure Composition of Different Asphalt Binder  
Nuclear Magnetic Resonance (NMR) is a phenomenon in which, when a sample is exposed to a radio-frequency electromagnetic field perpendicular to a strong external magnetic field, magnetic nuclei meeting resonance conditions absorb electromagnetic waves, resulting in a jump in nuclear energy levels. This process generates electromagnetic resonance signals corresponding to magnetism and provides information about characteristics and chemical structures in the induction coil perpendicular to the external magnetic field. Nuclear Magnetic Resonance Hydrogen Spectroscopy allows us to assess the chemical environments of different hydrogen atoms in asphalt binders. As hydrogen atoms occupy distinct chemical environments, they produce resonance peaks at varying positions, creating a chemical shift relative to a reference peak. We can deduce the position of hydrogen atoms within the carbon chain and analyze their molecular structure. This study classifies hydrogen types in the spectra into four categories: H\({}_{\Delta}\), H\({}_{\alpha}\), H\({}_{\beta}\), and H\({}_{Y}\), based on their chemical shifts, as presented in Table 3 and Figure 10.  
Figure 10: Positions of different hydrogen in nuclear magnetic resonance hydrogen spectra. \begin{table}
\begin{tabular}{c c c} \hline
**Hydrogen** & **Attribution** & **Chemical Shift, ppm** \\ \hline H\({}_{\Delta}\) & Hydrogen is directly linked to aromatic carbon & 6.3\(\sim\)9.3 \\ H\({}_{\alpha}\) & Hydrogen is linked to the \(\alpha\)-carbon of the & 2.0\(\sim\)4.0 \\  & aromatic ring & \\  & Hydrogen on the \(\beta\)-carbon of the aromatic ring & \\ H\({}_{\beta}\) & and the CH2 and CH groups farther from & 1.0\(\sim\)2.0 \\  & \(\beta\)-carbon & \\ H\({}_{Y}\) & Hydrogen in the \(\gamma\)-position of the aromatic ring & 0.5\(\sim\)1.0 \\  & and the CH3 group far from \(\gamma\) & \\ \hline \end{tabular}
\end{table} 
Table 3: \({}^{1}\)H-NMR spectral region delineation and attribution. Figure 9: G-R parameter of asphalt binder. accounting for approximately 60% of the total. This indicates that hydrocarbon elements in virgin asphalt are primarily structured as carbon chains. The hydrogen content at the \(\gamma\) and \(\alpha\) positions of the aromatic ring is relatively similar, ranging from 10% to 20%, suggesting a limited number of chain hydrocarbons in the asphalt binder. Hydrogen linked to the aromatic ring exhibits the lowest content. H\({}_{\rm A}\) content increased moderately in all asphalt binders after short-term aging, signifying a rise in the number of aromatic ring structures. Following O+UV-aging, there was a significant upsurge in H\({}_{\rm A}\) content, particularly in the \(\gamma\)-position of the aromatic ring compared to the \(\alpha\)-position. This suggests a notable increase in unbound carbon chains in the asphalt binder. The hydrogen distribution in Allaged asphalt binder closely resembled that of O+UV-aged asphalt binder, indicating that outdoor exposure leads to an increase in aromatic ring structures within the asphalt binder. Molecular chains undergo breakage and reorganization, resulting in longer carbon chains. Conversely, the impact of aromatic ring structure due to O-aging was less pronounced. The introduction of UV radiation increased the number of aromatic rings, reduced the presence of branched chains on the aromatic rings, and elevated the number of carbon chains not linked to the aromatic rings. During exposure, broken molecular chains and the original chains in the asphalt binder underwent additional polymerization reactions, transforming their structural forms into aromatic rings, cycloalkane aromatization, and ultimately forming more intricate ring structures. The \({}^{1}\)H-NMR spectra of SBS-modified asphalt binder are presented in Figure 12.  
Figure 12: The \({}^{1}\)H-NMR spectra of SBS-modified asphalt binder.