# Long-Term Monitored Road Degradation Functions as a Tool to Increase Quality of Pavement Design
## 2 Research Methods
### Results of Road Bearing Capacity
#### 3.3.1. Asphalt-Bonded Construction Layers  
As a general fact, the modulus of elasticity of asphalt-bonded road construction layers changes under the influence of temperature. The data were therefore divided into three temperature groups. The modulus of elasticity was then calculated for each group by regression analysis.  
1. Data group--road temperature 20.01-30.00 \({}^{\circ}\)C
2. Data group--road temperature 10.01-20.00 \({}^{\circ}\)C
3. Data group--road temperature 5.01-10.00 \({}^{\circ}\)C  
The most represented temperature group, which covers the whole evaluation period, is group no. 2 with road temperature during measurement 10.01-20.00 \({}^{\circ}\)C. The available measured data in this group are the period 1997-2018 and contain 12 representative values. The first temperature group contains only 6 representative values and temperature group no. 3 contains seven representative values. For this reason, data temperature group no. 2 was selected to assess the development of the modulus of elasticity of asphalt-bonded layers in the long-term section. The limit value was determined as 30% of the design value of the modulus of elasticity, i.e., 1650 MPa. Upon reaching this modulus of elasticity, the road is considered unsuitable for road traffic in terms of the modulus of elasticity. The mathematical evaluation of the dependence of the development of the modulus of elasticity recalculated by back-calculation, describes the polynomial dependence of the 3 rd degree. To recalculate the modulus of elasticity of the structural layers of the road, a calculation program was used, which works on the principle of creating a model of the road with a layered half-space. The interaction of the layers is simplified and the materials of the layers of the road structure are homogenized. Isotropy and flexibility of the half-space are also considered. The principle of calculation is based on the approximation of the calculated deflection curve to the measured deflection curve at the measuring point until the conditions of the permitted difference between the measured and calculated deflection curve are met. The load on the surface of the model must correspond to the load parameters when measuring the deflection with the FWD deflectometer. The radius of the loading surface of the road model must be equal to the radius of the load plate of the deflectometer. In the experiment, the road section was evaluated as one homogenized unit in the length of 1000 m with 51 evaluated points. After removing the local extremes from the input data, the back modulus of elasticity of the individual structural layers of the three-layer system was recalculated. For deflection curves, the procedure of creating an average deflection curve in one measured year was used. The input data entered (which remain unchanged) are as follows: uniform load; load ring radius; contact in the joints of structural layers; radial coordinates (representing the distance of the sensors from the load axis); vertical coordinates (representing the depth of the structural layers). The input data entered (whose values change in order to monitor the change in the shape of the deflection curve) are the modulus of elasticity of the structural layers; thickness of structural layers and Poisson's ratio. For Figures 11-14 in this section we state that \(y\) is modulus of elasticity, \(x\) is traffic load (mil. vehicles), \(y_{n/N}\) is modulus of elasticity depending on load n/N, where \(y_{t/T}\) is modulus of elasticity depending on load t/T and \(R^{2}\) is determination index.