# Low Temperature Resistance Increase for Bitumen by Compounding with Tar
## 3 Results and Discussion
### Chemical Structure of Bitumens
#### 3.3.2 Fragments of Molecules  
The spectra of atoms of hydrogen \({}^{1}\)H and carbon \({}^{13}\)C constructed according to the results of measurement of the corresponding chemical shifts for the virgin bitumen (a), tar (b) and the compounded bitumen (c) are shown in Figures 9 and 10. The contents of the nuclei \({}^{1}\)H and \({}^{13}\)C in the functional groups available in the tar, the virgin bitumen and the compounded one are shown in Tables 8 and 9. The obtained results show that despite the obvious change for the group chemical composition of the bitumen by means of compounding, the distributions of hydrogen atoms in aromatic and aliphatic fragments of molecules (in functional groups) of hydrocarbons in the virgin bitumen and the compounded one remain the same: in aromatic fragments--5.7%; in aliphatic fragments--94.3%. The highest contents (60%) are hydrogen atoms in methylene (CH\({}_{2}\)) and methine (CH) groups of saturated compounds; in methyl (CH\({}_{3}\)), methylene and methine groups in \(\beta\); and further positions to an aromatic ring. A quarter of the hydrogen atoms (25%) are in methyl groups in saturated compounds and \(\gamma\) and further positions to an aromatic ring. Only 9% of the hydrogen atoms are connected directly (at \(\alpha\) positions) to aromatic and carbonyl carbons, which areheteroatoms. It should be also noted that the distribution of hydrogen in the above tar fragments is practically the same as in the virgin bitumen and the compounded one. In both the virgin bitumen, tar and the compounded bitumen, no olefin group hydrogen atoms have been found. Similar results for a road bitumen and an industrial one have been obtained in the works [32; 39]. A marked change in bitumen compounding occurs in the distribution of carbon atoms in specific functional groups. Thus, the total content of carbon atoms in methyl groups (C\({}_{\text{pm}}\) + C\({}_{\text{pa}}\)) significantly decreased (35.1%). Meanwhile, carbon atoms in methyl groups \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type of Atoms** & **Bitumen** & **Tar** & **Compounded Bitumen** \\ \hline H\({}_{\alpha}\) & 9.0 & 9.8 & 9.2 \\ H\({}_{\beta}\) & 60.0 & 59.9 & 60.1 \\ H\({}_{\gamma}\) & 25.3 & 24.3 & 25.0 \\ H\({}_{\alpha\ell}\) & 94.3 & 94.0 & 94.3 \\ H\({}_{\text{ar}}\) & 5.7 & 6.0 & 5.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Functional groups (% under quantity of \({}^{1}\)H). Figure 10: \({}^{13}\)C NMR spectra of the bitumen (**a**), tar (**b**) and the compounded bitumen (**c**). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type of Atoms** & **Bitumen** & **Tar** & **Compounded Bitumen** \\ \hline C\({}_{\text{pm}}\) & 10.5 & 8.3 & 9.2 \\ C\({}_{\text{pa}}\) & 17.1 & 15.1 & 8.7 \\ C\({}_{\alpha\ell}\) & 72.4 & 76.6 & 82.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Functional groups (% under quantity of \({}^{13}\)C). bound to secondary and tertiary carbon atoms (or aromatic ring), compared to their content in the virgin bitumen, decreased by 12.4% and 49.1%, respectively. The quaternary carbon atoms (C\({}_{a,t}\)), on the contrary, significantly increased (by 13.4%). [PERSON] and [PERSON]. [40; 41], by dielectric measurements, found that methyl groups connected directly to the main chain of polymers limit considerably the mobility of macromolecules. The activation energy increase by 10-30% at replacement of one of hydrogen atoms with a methyl group in ethane molecule is mentioned in Reference [42]. The above phenomena of restriction for the mobility of macromolecules in polymers and the activation energy increase in ethane molecule are explained by so-called steric obstacles created by methyl groups [42; 43; 44]. It has been also found that the reduction in methyl groups increases the mobility of the polymer chains. Thus, copolymerization of methyl methacrylate with styrene, which reduces the number of methyl groups, causes the decrease in the relaxation time, i.e., it increases the mobility of polymer units [40].