## 3 Results and Discussion
### Stiffness Modulus  
Stiffness curves derived from the results of the two creep tests--the Bending Beam Creep Test (BBCT) and the Tensile Creep Test (TCT)--for all the tested materials are presented in Figures 6-9. In the case of the Bending Beam Creep Test, the presented results are the mean values from 5 different specimens (coefficient of variation for all test results is in the range from 5 to 25%; mean 10%). In the case of the Tensile Creep Test, the presented results are the mean values from 2 to 4 different specimens (coefficient of variation for all test results is in the range from 1 to 40%; mean 15%). For the asphalt mixture AC 11W with neat bitumen 35/50, only the Tensile Creep Test was conducted.  
Stiffness curves derived from both creep tests differ at all the tested temperatures--both by shape and by values. For low temperatures (\(-10\)\({}^{\circ}\)C and lower) results obtained from the TCT present higher values of stiffness modulus. The situation is opposite at temperatures higher than 0 \({}^{\circ}\)C, where results obtained from the BBCT present higher values. The difference in both cases is around 50% and will be discussed in detail further in the paper.  
In terms of shape of the stiffness curves, two main differences are visible between the two tests: the shape of the stiffness curve at the highest temperature as well as the occurrence and shape of deviations from the time-temperature superposition principle. As shown in Figures 6b and 7b, for the temperature of +20 \({}^{\circ}\)C the stiffness curve derived from the TCT bends from a straight line for long times of loading. Such a shape is beneficial for construction of the master curve--it is easier to develop the equation for a typical sigmoidal shape, where \"Max\" and \"\(\delta\)\" master curve parameters could have physical meaning of maximum and minimum stiffness modulus. In the case of BBCT test trials at +20 \({}^{\circ}\)C for the lowest possible stress, the results suggested destruction of the specimen for times of loading longer than 200 s (stiffness moduli reached value of \(\sim\)1 MPa). Therefore, in the case of BBCT, it is much harder to derive the \"\(\delta\)\" master curve parameter, which corresponds to the lowest value. As for the appearance of deviations--previous studies [40; 54] showed that in the case of BBCT test, deviations appeared after around 500 s of loading. Their shape suggested that the curve was approaching a horizontal asymptote. Such results were confirmed in other studies [10; 39]. In the case of the TCT test, deviations from the time-temperature superposition principle were also observed for most cases (except for the AC 115 45/80-55 MT mixture) at temperatures of \(-10\)\({}^{\circ}\)C and lower. However, first analyses showed that they occur earlier (around 200-300 s) and the shape  
Figure 8: Creep test results—stiffness curves for AC 11W 35/50 MT, only for TCT.  
Figure 9: Creep test results—stiffness curves for AC 11S 45/80-55 MT (**a**) BBCT; (**b**) TCT.  
is different--after the \"asymptotical\" phase, which lasts around 1000-3000 s, the modulus starts to decrease again. As further tests will be conducted on other mixtures, deviations will be analyzed in detail in future studies.