# Accelerated Creep of Asphalt Concrete at Medium Temperatures
## 4 Results and Discussion
### Time Characteristics  
The following time characteristics of accelerated creep are important from a practical point of view: (1) the start time of the accelerated creep section (the end of the steady-state creep section) t\({}_{2}\) is the time counted from the moment of the end of loading of a test specimen until the start of the accelerated creep; (2) the end time of the accelerated creep section (long-term strength) tf is the time counted from the moment of the end of loading of a specimen until its complete failure; (3) the duration of the accelerated creep section \(\Delta\)t\({}_{23}\) which is determined by the formula:  
\[\Delta\)t\({}_{23}=\)t\({}_{f}-\)t\({}_{2}. \tag{8}\]  
The dependences of the time characteristics t\({}_{2}\) and tf on stress are shown in Figures 12 and 13, where it is evident that they are described with high accuracy by a power function. A strong influence of stress occurs at its small values (up to 0.3 MPa). With an increase in stress from 0.084 MPa to 0.3 MPa (by 3.6 times), the characteristic times t\({}_{2}\) and tf decrease by three orders of magnitude, i.e., by thousands of times; with a further change in stress from 0.3 MPa to 0.6 MPa, the times t\({}_{2}\) and tf decrease by five times.  
Figure 12: Dependence of the start time of accelerated creep section t\({}_{2}\) on stress.  
Figure 13: Dependence of the end time of the accelerated creep section t\({}_{f}\) (long-term strength) on stress.  
It should be noted that the values of the exponents in the formulas in Figures 12 and 13, equal to 3.11 and 3.01, respectively, are very close. The slight difference in their values can be explained by the scatter of experimental results. Then, for both dependencies, these exponents can be taken to be the same and equal to their arithmetic mean values: \((3.11+3.01)/2=3.06\).  
Using Formula (8), the duration of the accelerated creep section can be calculated:  
\[\Delta t_{23}=7.15\cdot\sigma^{3.06}-4.63\cdot\sigma^{3.06}=2.52\cdot\sigma^{3.06}. \tag{9}\]  
The relative duration of the accelerated creep section:  
\[\frac{\Delta t_{23}}{t_{f}}=\frac{2.52\cdot\sigma^{3.06}}{7.15\cdot\sigma^{3.0 6}}=0.35. \tag{10}\]  
Thus, it has been established that the relative duration of the accelerated creep of asphalt concrete at temperatures of 22-24 \({}^{\circ}\)C does not depend on stress and is equal to 35% of the long-term strength.  
A joint consideration of the experimental results obtained in Sections 4.2 and 4.3 allows us to formulate the following important finding: the deformation characteristics of the accelerated creep of asphalt concrete change only at low (up to 0.2 MPa) stresses, while at medium and high stresses (from 0.2 MPa to 0.6 MPa) they remain practically constant. The latter can be explained by the fact that, with an increase in stress, the effect of increasing the deformation rate and the effect of reducing the duration of the accelerated creep period are completely mutually compensated; in other words, with an increase in stress, due to a reduction in the time of action of the load, the strain does not have time to develop. This finding is of great practical importance, as, since the processes of damage accumulation and destruction of asphalt concrete pavements are significantly influenced by the values of the load from the axles (wheels) of vehicles, in models of road pavements, including tensile strain in asphalt concrete layers, the values of the deformation characteristics of asphalt concrete can be taken as the same for medium and heavy vehicles.