## 1 Introduction
### Methods
#### 2.2.2 Mechanical Performance Test  
(1) Improvement of shear test  
According to existing specifications [21; 22], a uniaxial penetration test and triaxial compression test are used for determining the overall shear strength of the asphalt mixture. However, their test results are not capable of reflecting the changes in the shear strength with the depth of the pavement. Therefore, in order to investigate the decay law of the shear strength of the asphalt mixture with the depth of the pavement under high humidity and at high temperatures, this paper improved the test method by cutting the specimen into layers, changing the size of the specimen, and indenter and adding a base layer. Improved test specimens were prepared using the double-layer rutted specimen upper layer cut method. Layers 1-4 were cut at a uniform depth. Each layer had a length, width, and height of 70 mm, 70 mm, and 11 mm. The steel mold base had a length, width, and height of 70 mm, 70 mm, and 40 mm. The interior contained holes 40 mm in diameter. The diameter of the base of the indenter is 20 mm. The test temperature was 15\({}^{\circ}\)C. The loading rate was 10 mm/min. The test process is shown in Figure 3. The shear strength is calculated by:  
\[\tau=\frac{P}{2\pi r\cdot h} \tag{1}\]  
where \(\tau\) is the shear strength (MPa), \(P\) is the maximum damage load (kN), \(r\) is the indenter radius (mm), \(h\) is the height of the specimen, and \(D\) is the decay degree of the mechanical properties, which can be calculated by:  
\[D=\left(1-\frac{Measured\ valued}{Standard\ valued}\right)\times 100 \tag{2}\]  
where \(D\) is the decay degree of mechanical strength (%). The standard value of mechanical strength is the average value of mechanical strength from Cut Layers 1 to Cut Layer 4 when the number of sizeable wet temperature cycles is 0.  
Figure 3: Shear test procedure. (**a**) Schematic diagram of shear test, (**b**) actual working diagram, (**c**) diagram of specimen damage.  
2. Improvement of flexural-tensile test of small beam According to existing specifications [21], a flexural-tensile test was performed on small beams to evaluate the flexural-tensile properties of the asphalt mixture. However, the test results were primarily used to assess the flexural-tensile properties of the whole rutted specimen, which cannot reflect those of the mixtures at different depths. Therefore, in order to investigate the decay law of the flexural-tensile properties of the asphalt mixture with the depth of pavement under the action of a sizeable wet temperature cycle, the flexural-tensile test was modified in this paper by reducing the beam thickness and increasing the beam width to change the size of the specimen. The cut mode of the modified specimens was the same as that of the shear test. The length, width, and height of the final shear specimen were 90 mm, 50 mm and 11 mm, respectively, and the span diameter was 70 mm. The test temperature was 15 \({}^{\circ}\)C and the loading rate was 10 mm/min. The test process is specified in Figure 4. The flexural-tensile strength and modulus were calculated with reference to specification [21]. The decay degree was calculated by Equation (1).