## 3 Results
### Analysis of Hot Recycled Mixture Based on CAM Model
#### 3.4.2. Creep Characteristics  
The deformation characteristic of an asphalt mixture is the external manifestation of its internal viscoelasticity. Studying the viscoelastic change in a reclaimed asphalt mixture in the process of low-temperature creep is helpful to understand and explain its low-temperature deformation behavior essentially. The viscoelastic characteristics of an asphalt mixture can be obtained based on the Burgers model, which also reflects the creep and stress relaxation behavior of an asphalt mixture, as shown in Equations (5) and (6) [29]. \[J(t)=\frac{\varepsilon(t)}{\sigma_{0}} \tag{5}\]  
\[J(t)=\frac{t}{\eta_{1}}+\frac{1}{E_{1}}+\frac{1}{E_{2}}(1-e^{-\frac{E_{2}}{ \eta_{2}}t}) \tag{6}\]  
where \(J(t)\) is creep compliance; \(\varepsilon(t)\) is stress; \(\sigma_{0}\) is stress; and \(E_{1}\), \(E_{2}\), \(\eta_{1}\), and \(\eta_{2}\) are the elastic modulus and viscosity coefficient, respectively. 1 stOpt software was used to nonlinearly fit the creep behavior of the asphalt mixtures, and the Burgers model parameters \(E_{1}\), \(E_{2}\), \(\eta_{1}\), \(\eta_{2}\) could be obtained. Based on the model parameters, the relaxation time of the asphalt mixtures under different stress levels could be obtained: \(\tau=\eta_{1}/E_{1}\)[30]. The calculation results of relaxation time are shown in Figure 10.  
Relaxation time is an important parameter to characterize the change in internal stress of materials over time. The shorter the relaxation time, the faster the dissipation of the internal stress of materials and the better the cracking resistance at low temperature. As can be seen from Figure 8, the addition of a regenerant significantly reduces the relaxation time of the asphalt mixtures. Under the stress levels of 0.8 MPa, 1.6 MPa, and 2.4 MPa, the relaxation time of the petrochemical-oil-based reclaimed asphalt mixture is reduced by 45%, 12%, and 8%, and that of the waste-palm-oil-based reclaimed asphalt mixture is reduced by 51%, 14%, and 61%, respectively. At the same time, with the increase in the stress level, the relaxation time of the three asphalt mixtures decreases gradually. According to the  
Figure 9: Phase angle master curve fitting parameters. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Mixture Type** & \(\delta_{\pi}\)_/\({}^{c}\)_ & \(f_{d}\)/Hz & \(m_{d}\) & \(R_{d}\) & **Goodness** \\ \hline RAP & 33.12 & 0.0026 & 3.171 & 4.483 & 0.960 \\ RAP + PCO & 35.09 & 0.4576 & 6.041 & 6.393 & 0.978 \\ RAP + WPO & 37.94 & 0.2223 & 4.132 & 4.904 & 0.988 \\ \hline \end{tabular}
\end{table} 
Table 7: Phase angle master curve fitting parameters. study, stress and temperature have equivalent effects; that is, the higher the temperature and the greater the stress, the larger the creep strain of the mixture and the shorter the corresponding relaxation time. In the Burgers model, a spring and a clay pot are used to represent the storage and consumption capacity of materials, respectively. [PERSON] et al. established the storage and dissipation energy of materials through the model parameters [PERSON] et al. (2011); [PERSON] et al. (2011); [PERSON] et al. (2011) shown in Equations (7) and (8). \[\mathrm{W_{s}}(t)=\sigma_{0}^{2}[\frac{1}{E_{1}}+\frac{1}{2E_{2}}(1-2e^{- \frac{E_{2}}{\eta_{2}}t}+e^{-\frac{2E_{2}}{\eta_{2}}t})] \tag{7}\]  
\[\mathrm{W_{d}}(t)=\sigma_{0}^{2}[\frac{1}{\eta_{1}}+\frac{1}{2E_{2}}(1-e^{- \frac{2E_{2}}{\eta_{2}}t})] \tag{8}\]  
where \(\mathrm{W_{s}}\) is stored energy and \(\mathrm{W_{d}}\) is dissipated energy. The dissipated energy ratio is the ratio of dissipated energy to stored energy, which is also an important index reflecting the stress relaxation ability of materials. The higher the dissipation energy ratio, the better the low-temperature cracking resistance of an asphalt mixture. It can be seen from the formula that the dissipated energy ratio is a function of time.