## 3 Results  
### Carbonyl and Sulfoxide Indices  
The following section investigates the relative changes in the I\({}_{\text{C=O}}\) and I\({}_{\text{S=O}}\) indices relative to the non-aged reference binders (without additives). The corresponding statistical models approximating the values of the indices and their regression coefficients are evaluated in the provided tables. Figure 3 presents changes in the values of the carbonyl index as a function of the investigated additives' (additive A and B) content, and Table 5 shows the statistical analysis of these effects. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Structural Index**} & \multirow{2}{*}{**Bond**} & \multicolumn{2}{c}{**Characteristic Peak**} & \multirow{2}{*}{ \begin{tabular}{c} **Structural Index** \\ **Wave Number (cm\({}^{-1}\))** \\ \end{tabular}  } \\  & & & \\ \hline Sulfoxide & S=O, stretching & 1030 & \(I_{S=O}=\frac{A_{A_{A_{A_{A_{A_{A_{A_{A_A}_A_A_A_A_A_A_A_A_A_A_A_A_A_A_A_AA_A_A_A_A_AA_A_A_A_A_A_  
Analysis of the plots presented in Figure 3 shows both similarities and distinctions between the effects of the evaluated additives depending on the type of base asphalt binder. It can be clearly seen that both additives resulted in a decrease in the carbonyl index in non-aged and RTFOT-aged binders. On the other hand, after PAV ageing, a significant rise in this parameter was observed when the additives were present in the binders--particularly in the case of the 45/80-55 PMB. The lowest values of the carbonyl index in the 50/70 binder before ageing were observed when the additives were used separately, at the maximum dosing (0.3% and 2% of additives A and B, respectively). After short- and long-term ageing, the lowest values were observed when 0.15% of additive A was used alone and in conjunction with 2% of additive B. Intermediate values were seen when the additives were used simultaneously in the mid-range of dosing (0.15% and 1%). High values of I\({}_{\text{C=O}}\) were associated with high dosages of additive B. In the case of the 45/80-55 polymer-modified binder, the effects of the additives were much more varied in different ageing statesof the binders. Before ageing, the lowest values of the carbonyl index were observed when simultaneously 0.15% of additive A and 2% of additive B were used. After RTFOT ageing, it was the maximum dosing of additive A alone which yielded this minimum. After the PAV ageing on the other hand, any combination of  
Figure 3: Surface plots of the changes in the carbonyl index in 50/70 and 45/80-55 asphalt binders in response to the investigated additives and laboratory ageing. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**I\({}_{\text{C=O}}\)** & **Ageing: None** & **Ageing: RTFOT** & **Ageing: RTFOT+PAV** \\
**Effect:** & **50/70** & **45/80-55** & **50/70** & **45/80-55** & **50/70** & **45/80-55** \\ \hline Intercept & 0.003 *** & 0.001 *** & 0.003 *** & 0.002 *** & 0.004 *** & 0.003 *** \\ Additive A & \(-\)0.020 *** & \(-\)0.008 *** & \(-\)0.021 *** & \(-\)0.001 *** & \(-\)0.018 *** & 0.021 *** \\ Additive B & \(-\)0.002 *** & \(-\)0.0003 *** & 0.001 *** & \(-\)0.001 *** & \(-\)0.004 *** & 0.0002 * \\ (Additive A)\({}^{2}\) & 0.030 *** & 0.035 *** & 0.059 *** & \(-\)0.013 *** & 0.053 *** & \(-\)0.053 *** \\ (Additive B)\({}^{2}\) & 0.0004 *** & 0.0002 *** & \(-\)0.001 *** & 0.0003 *** & \(-\)0.002 *** & 0.0002 \\ A:B interaction & 0.008 *** & \(-\)0.002 *** & 0.002 *** & 0.004 *** & \(-\)0.0001 & \(-\)0.0003 \\ \hline Observations & 27 & 27 & 27 & 27 & 27 & 27 \\ R\({}^{2}\) & 0.999 & 0.999 & 0.998 & 0.997 & 0.997 & 0.989 \\ Adjusted R\({}^{2}\) & 0.999 & 0.998 & 0.998 & 0.996 & 0.996 & 0.986 \\ \hline \hline \end{tabular} Note: *-\(p\leq 0.05\); **-\(p\leq 0.01\); ***-\(p\leq 0.001\).  
\end{table} 
Table 5: A summary of the statistical models approximating the values of the carbonyl index measured in the 50/70 and 45/80-55 asphalt binders.