# Accelerated Creep of Asphalt Concrete at Medium Temperatures
## 3 Accelerated Creep  
### Creep Curve Characteristics  
A typical asphalt concrete creep curve has three characteristic sections (Figure 5): I--section of unsteady-state creep; II--section of steady-state creep; III--section of accelerated creep. The characteristics of the creep curve and their brief descriptions are given in Table 1.  
As stated in [7], in the unsteady-state creep section, the process of asphalt concrete strengthening occurs as a result of the strain rate decreasing over time. In the steady-state creep section, the deformation process occurs at a constant rate. It is assumed that, in this section, the number of broken bonds in the structural elements of asphalt concrete (destruction) is equal to the number of restored bonds per unit of time. In the accelerated  
Figure 4: Scheme of testing the asphalt concrete samples for creep.  
Figure 5: Characteristics of an asphalt concrete creep curve.  
creep section, irreversible accumulation of damage begins in places of stress concentration (pores, microcracks); this results in a macroscopic crack forming by merging some of the specified defects. Then, the macroscopic crack spreads (grows) and, at the end of the accelerated creep section, complete failure of the material occurs (division of the asphalt concrete sample into parts) [10].  
It is known that one of the main types of destruction of road asphalt concrete pavement is fatigue cracking (Figure 6a) [35]. In regions with cold winter climates, low-temperature cracking of asphalt concrete pavements occurs (Figure 6b). Therefore, we believe that, in the study of the strength and durability of asphalt concrete, it is important to model the accelerated creep and determine the parameters characterizing accumulation of damage and destruction at this stage.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Characteristic** & **Characteristic Name** & **Brief Description** \\ \hline I & section of unsteady-state creep & the first section of creep curve within which strain rate decreases \\ II & section of steady-state creep & the second section of creep curve within which strain rate is constant \\ III & section of accelerated creep & the third section of creep curve within which strain rate increases; at the end of this section the test specimen fails the value of \(\varepsilon_{0}\) depends on magnitude and duration (rate) of full load application \\ \(\varepsilon_{1}\) & strain at the end of section I (at the beginning of section II) of creep curve; limiting strain of hardening & maximum strain in section I (minimum strain in section II) of creep curve \\ \(\varepsilon_{2}\) & strain at the end of section II (at the beginning of section III) of creep curve & maximum strain in section II (minimum strain in section III) of creep curve \\ \(\varepsilon_{t}\) & failure strain & maximum strain on creep curve (also in section III) corresponding to failure time tf \\ \(\Delta\varepsilon_{23}\) & total strain of accelerated creep & total strain realized in section of accelerated creep \\ \(\mathrm{t}_{1}\) & unsteady-state creep duration; limiting time of hardening & at this time point unsteady-state creep ends; from this time point steady-state creep begins \\ \(\mathrm{t}_{2}\) & the moment in time corresponding to the end of steady-state creep and the beginning of accelerated creep & at this time point steady-state creep ends; from this time point accelerated creep begins \\ \(\mathrm{t}_{t}\) & failure time & t this time point failure of the test sample occurs \\ \(\Delta\mathrm{t}_{23}\) & accelerated creep duration & during this period of time accelerated creep is realized \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characteristics of an asphalt concrete creep curve and their brief descriptions.  
Figure 6: Destruction of road asphalt concrete associated with accelerated creep: (**a**)—fatigue cracking; (**b**)—low-temperature cracking.