## 2 Materials and Methods
### Methods  
#### 2.2.1 Tensile Creep Test (TCT)  
Tensile creep properties of asphalt mixtures at low temperatures were assessed by means of the Tensile Creep Test (TCT) method according to EN 12697-46 standard [49]. In the TCT, the specimen is subjected to a constant tensile stress \(\sigma\) at a constant temperature \(T\). The progression of the strain \(\varepsilon\) with time is recorded. According to the standard, it is recommended to maintain the constant load for 8 h and, after unloading, record the regression for additional 2 h. The principle of the TCT is shown in Figure 1.  
In the TCT method, the specimens were loaded in order to achieve a constant tensile stress at a constant temperature. The stress levels were determined in relation to tensile strength results from the Uniaxial Tension Stress Test (UTST). In the UTST, a specimen is pulled with a constant strain rate at a constant temperature until failure. Results of the UTST are: the maximum stress (tensile strength) \(\beta_{t}(T)\) and the corresponding tensile failure strain \(\varepsilon_{failure}(T)\) at the test temperature \(T\). In this research, the Tensile Stress Restrained Specim Test (TSRST) method was used as well. The results from the TSRST were compared to thermal stresses calculated based on the results from the creep test methods. The results of the TSRST procedure are: the progression of the thermal stress over the temperature \(\sigma_{cry}(T)\) and the failure stress \(\sigma_{cry}\), \(\mu_{failure}(T)\) at the failure temperature \(T_{failure}\). The results from the UTST and TSRST have been published and discussed in a separate paper [6]. In the TCT method, the level of the stresses applied was determined as the percentage of the maximum stress \(\beta_{t}(T)\) from the UTST at a given test temperature. Temperatures and stresses applied in the TCT are presented in Table 3 and in Figure 2. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & & **Type of Mixtures** & \\ \hline
**Asphal Mixture** & **AC 11 S** & **AC 11 S** & **AC 11 W** \\ \hline Type of layer & wearing course & wearing course & binder course \\ Type of traffic & low traffic (LT) & medium traffic (MT) & medium traffic (MT) \\ Bitumen type & 70/100 & 50/70 & 35/50 \\ Binder content (\% by mass) & 5.8 & 5.6 & 5.6 \\ Aggregate type & crushed gravel & crushed genesis & crushed genesis \\ Filler type & limestone & limestone & limestone \\ \hline Sieve size (mm) & & \% Passing (by mass) & \\ \hline
16 & 100 & 100 & 100 \\
11.2 & 97 & 98 & 98 \\
8 & 83 & 77 & 83 \\
5.6 & 71 & 62 & 65 \\
4 & 60 & 52 & 54 \\
2 & 40 & 39 & 43 \\
0.125 & 11 & 11 & 12 \\
0.063 & 8.0 & 7.2 & 7.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Properties of asphalt mixtures. Figure 1: Principle of the Tensile Creep Test (TCT); where: **X**–time, **Y1**–strain, **Y2**–temperature, **Y3**–stress, [49]. The specimens were tested using a \"TSRST-MULTI\" Multi Station Thermal Asphalt System (PAVETEST, Italy) device with servo hydraulic equipment. The equipment and test setup used are presented in Figure 3.  
Figure 3: Tensile Creep Test (TCT) and Uniaxial Tension Stress Test (UTST) setup: (**a**) photograph of the specimens during the test, (**b**) schematic view. \begin{table}
\begin{tabular}{c c} \hline \hline
**Test Temperature \(T\), \({}^{\circ}\)C** & \begin{tabular}{c} **Percentage of the Maximum Stress \(\beta_{t}\)(\(T\)) Obtained** \\ **from the UTST, \%** \\ \end{tabular} \\ \hline \hline \
\begin{tabular}{c} +20 \\ +5 \\ \(-10\) \\ \(-20\) \\ \(-30\) \\ \end{tabular} &
\begin{tabular}{c} 5 \\ 10 \\ 30 \\ 50 \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Test conditions for the Tensile Creep Test (TCT), [49]. Figure 2: Stress levels at test temperatures applied in the Tensile Creep Test (TCT). Three specimens were tested for each asphalt mixture and test temperature (both in the TCT or the UTST).