# Value-Added Use of Waste PET in Rubberized Asphalt Materials for Sustainable Payement
## 3 Results and Discussion
### Putting Resistance of CRMA Mixtures Incorporating PET Additives  
The 60 \({}^{\circ}\)C wheel tracking deformation results of the studied CRMA mixtures incorporating PET additives inside the binders are displayed in Figure 6, and the fitted non-linear curve equations used to predict the rut development for all mixtures are presented in Table 7. As depicted, the rut depth of the 18 CRMA mixture is slightly increased when PET additives are used, and there is no significant difference in rutting depth between the 18 CRMA2 PET-TETA and 18 CRMA2 PET-EA mixtures. Meantime, all mixtures have rutting depths of less than 4 mm at the end of the loading cycle at 60 \({}^{\circ}\)C. The results demonstrate that PET additives slightly compromise the rutting deformation resistance of the 18 CRMA mixture but have no significant influence on the practical applications of the target mixtures under environmental temperatures in terms of rutting behavior. In addition, with the elapsing time under the same conditions, the trends of the rut development of these mixtures are in good compliance with the fitted non-linear curve equations because the correlation coefficient (R\({}^{2}\)) reaches 0.998. Furthermore, it is possible to predict the rut development and rate of change under the same conditions based on the fitted results obtained.  
Figure 5: Marshall stability (**a**) and flow value (**b**) of rubberized asphalt mixtures incorporating PET additives.  
According to the rutting slab tests, the rate of rut development can be calculated by Equation (9):  
\[R_{rd}=\frac{RD_{i}}{t_{i}} \tag{9}\]  
where \(R_{rd}\) means the rate of rut development, mm/min; \(RD_{i}\) means the rut depth, mm; and \(t_{i}\) means the elapsed time, min.  
Based on the data, fitted equations, and calculation formula above, the changes in the \(R_{\text{rd}}\) of these mixtures with the loading time are plotted in Figure 7. Clearly, the \(R_{\text{rd}}\) value of the 18 CRMA mixture becomes slightly larger when the 2 wt.% PET additives are used, and similar \(R_{\text{rd}}\) values for the 18 CRMA2 PET-TETA and 18 CRMA2 PET-EA mixtures are also observed. In addtion, it is evident that the \(R_{\text{rd}}\) values of all three mixtures are less than 0.5 mm/min, even at the very beginning of the loading cycle. These results indicate that both PET-TETA and PET-EA will slightly compromise the rutting resistance of the 18 CRMA mixture, but the difference is not significant. In addition, it is worth noting that the use of PET additives leads to an opposite subtle change in the high-temperature properties between the asphalt binder and the mixture. The reason for this phenomenon is that the incorporation of PET-TETA somewhat improves the rheological properties of the rubberized binder at the testing temperature, and PET-EA has a relatively poor capacity to enhance the bonding properties of the rubberized binder with aggregates. Overall, these two types of PET additives do not significantly increase the high-temperature susceptibility of the original rubberized asphalt mixture in rutting deformation, so they will not affect the engineering applications of rubberized asphalt mixtures.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Sample** & **Non-Linear Fitted Curve Equation** & \(R^{2}\) & **Fitting Equation** & **Remarks** \\ \hline
18 CRMA & y = 0.95 + 0.55 ln(x + 0.18) & 0.998 & \\ \hline
18 CRMA2 PET-EA & y = 1.11 + 0.68 ln(x + 0.20) & 0.998 & \
\begin{tabular}{c} y = a \(-\) b\(\cdot\)ln(x + c) \\ (x \(\
eq\) 0) \\ \end{tabular} &
\begin{tabular}{c} y: rut depth, mm \\ x: elapsed time, min \\ \end{tabular} \\ \hline
18 CRMA2 PET-TETA & y = 1.17 + 0.64 lnx & 0.998 & \\ \hline \end{tabular}
\end{table}
Table 7: Non-linear fitted curve equations of rut development for the studied mixtures.  
Figure 6: Rut depth development of CRMA mixtures containing PET additives at 60 \({}^{\circ}\)C.