## 3 Results
### Carbonyl and Sulfoxide Indices
the additives resulted in an increase in the values of the carbonyl index, specifically when both additives were present in high dosages. The summary of the statistical models (Table 5) shows that both additives had significant effects on the measured changes in the carbonyl index (\(p\leq 0.05\)). In the case of the RTPOT+PAV aged binders, the interaction effect was not confirmed to be statistically significant. Figure 4 presents changes in the values of the sulfoxide index as a function of the investigated additives' (additive A and B) content and Table 6 shows the statistical analysis of these effects. The effects of the additives on the sulfoxide indices were similar in both binders before ageing and after the short-term RIFOT ageing procedure. In general, the addition of additive A resulted in a decrease in the sulfoxide index although, in the non-aged asphalt binders, this effect was the largest in magnitude. The use of additive B on its own caused large increases in this index before ageing, but this effect was limited by the increasing concentration of additive A. After the RIFOT ageing, additive B had only minor effects on this index. After long-term PAV ageing of the 50/70 asphalt binders, the largest decrease in the sulfoxide indices was observed when additive B was set at 1% with additive A at \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multicolumn{1}{c}{**Is-o**} & \multicolumn{2}{c}{**Ageing none**} & \multicolumn{2}{c}{**Ageing: RTFOT**} & \multicolumn{2}{c}{**Ageing: RTFOT+PAV**} \\
**Effect** & **50/70** & **45/80-55** & **50/70** & **45/80-55** & **50/70** & **45/80-55** \\ \hline Intercept & 0.008 *** & 0.008 *** & 0.005 *** & 0.005 *** & 0.007 *** & 0.007 *** \\ Additive A & \(-\)0.046 *** & \(-\)0.049 *** & \(-\)0.008 *** & \(-\)0.006 *** & 0.011 *** & \(-\)0.006 *** \\ Additive B & 0.001 *** & 0.001 *** & \(-\)0.003 *** & \(-\)0.0001 & \(-\)0.002 *** & \(-\)0.0003 *** \\ (Additive A)\({}^{2}\) & 0.105 *** & 0.120 *** & 0.016 *** & 0.005 *** & \(-\)0.041 *** & 0.004 *** \\ (Additive B)\({}^{2}\) & \(-\)0.001 *** & \(-\)0.003 *** & 0.001 \(\,\) & \(-\)0.0001 \(\,\) & 0.001 *** & \(-\)0.0001 \(\,\) \\ A:B interaction & 0.0004 * & \(-\)0.001 *** & 0.0004* & 0.002 *** & \(-\)0.00004 & 0.002 *** \\ \hline Observations & 27 & 27 & 27 & 27 & 27 & 27 \\ R\({}^{2}\) & 0.998 & 0.998 & 0.962 & 0.966 & 0.962 & 0.938 \\ Adjusted R\({}^{2}\) & 0.998 & 0.997 & 0.953 & 0.958 & 0.954 & 0.923 \\ \hline \hline \end{tabular} Note: \(\dashp\leq 0.1\); \(\dashp\leq 0.05\); *\(\dashp\leq 0.01\); ***\(\dashp\leq 0.001\).  
\end{table} 
Table 6: A summary of the statistical analysis (analysis of variance) on the investigated additives’ effects on the values of the sulfoxide index measured in the 50/70 and 45/80-55 asphalt binders. Figure 4: Surface plots of the changes in the sulfoxide index in 50/70 and 45/80-55 asphalt binders in response to the investigated additives and laboratory ageing. 0% or 0.3%. Otherwise, the index increased significantly when 0.15% of additive A was used. In the case of the 45/80-55 asphalt binder, the decreases in the sulfoxide index were mainly associated with high dosing of additive A although additive B also contributed constructively to these effects. The results of statistical analyses provided in Table 6 show that in all cases, both additives contributed to the changes in the values of the sulfoxide index observed in both binders. The interaction between the additives was not proven to be statistically significant only in the case of the 50/70 paving-grade bitumen after PAV ageing. Table 7 shows the values of carbonyl and sulfoxide indices and their changes at the corners and centerpoint of the experimental plan to evaluate the magnitudes of the described effects directly using measured data. In the case of asphalt binders without additives, increases in both indices were seen as the ageing procedures were conducted.