## 4 Discussion  
This study has shown that the use of the investigated additives significantly affected the FTIR absorption bands associated with the carbonyl and sulfoxide structures forming in neat asphalt binders due to oxidative ageing (RTFOT and PAV). These values of the carbonyl and sulfoxide indices measuring relative changes in the contents of these species generally decreased after the introduction of both additives in neat asphalt binders and after RTFOT, by as much as 89%. After PAV ageing, the carbonyl and sulfoxide indices increased in most blends and the magnitude of this increase was generally related to the amount of the additives. On the other hand, in reference binders without additives, these indices gradually increased with the induced oxidative stress.  
The additives had far smaller effects on the measurements of the polybutadiene and polystyrene structural indices.  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & \multicolumn{4}{c}{**Pearson Correlation Coefficient R: 50/70**} \\  & **G*/sin(s)** & **J\({}_{\text{nr\_32 kPa}}\)** & **R\({}_{\text{32 kPa}}\)** & **I\({}_{\text{S-O}}\)** & **I\({}_{\text{C=O}}\)** \\ \hline
**G*/sin(s)** & 1 & \(-\)0.62 ** & 0.85 *** & 0.22 & 0.29 \\
**J\({}_{\text{nr\_32 kPa}}\)** & \(-\)0.62 ** & 1 & \(-\)0.59 ** & \(-\)0.28 & \(-\)0.4 \({}^{\prime}\) \\
**R\({}_{\text{32 kPa}}\)** & 0.85 *** & \(-\)0.59 ** & 1 & 0.16 & 0.44 \({}^{\prime}\) \\
**I\({}_{\text{S-O}}\)** & 0.22 & \(-\)0.28 & 0.16 & 1 & 0.24 \\
**I\({}_{\text{C=O}}\)** & 0.29 & \(-\)0.4 \({}^{\prime}\) & 0.44 \({}^{\prime}\) & 0.24 & 1 \\ \hline \hline \end{tabular} Note: \({}^{\star}\)—\(p\leq\) 0.1; \({}^{\star}\)—\(p\leq\) 0.01; \({}^{\star}\)—\(p\leq\) 0.001.  
\end{table}
Table 10: Correlation matrix of the performance parameters and FTIR chemical indices calculated for the 50/70-based asphalt binders before and after RTFOT.  
\begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Pearson Correlation Coefficient R: 45/80-55**} \\  & **G*/sin(s)** & **J\({}_{\text{nr\_32 kPa}}\)** & **R\({}_{\text{32 kPa}}\)** & **I\({}_{\text{S-O}}\)** & **I\({}_{\text{C=O}}\)** & **I\({}_{\text{PS}}\)** \\ \hline
**G*/sin(s)** & 1 & \(-\)0.65 ** & 0.56 * & 0.03  
Provided that even before laboratory ageing significant changes were seen in all structural indices, it can be concluded that the additives influenced the measurements based on the evaluated FTIR spectral bands. It should be noted that the FTIR spectrum of additive A is characterized by substantial absorption peaks in the carbonyl and sulfoxide bands, while additive B (identified as a form of polyethylene) may degrade due to oxidation to ketones, carboxylic acids and esters [75]. These effects may contribute to the effects seen in the carboxyl and sulfoxide spectral bands.  
It was also assessed that the apparent changes in the chemical composition of the asphalt binders after oxidative (RTFOT) ageing were not followed by the changes in the rheological performance of the binders in high temperatures. These discrepancies in the changes in the high-temperature performance and apparent changes in chemical composition as a result of oxidative ageing measured by the FTIR indices may be the cause of the lack of correlations between the measured performance parameters and FTIR indices.