## 2 Materials and Methods  
The size of the composite structure specimen was 300 \(\times\) 90 \(\times\) 100 mm\({}^{3}\). The concrete composite had two or three layers: The No SAL type had a 50 mm AC-13 (a type of asphalt concrete) surface (layer I), and a 50 mm cement concrete layer (layer II); the HVASAAL type had a 30 mm AC-13 surface (layer I), a 20 mm HVASAAL (layer II), and a 50 mm cement concrete layer (layer III); the RASAL type had a 30 mm AC-13 surface (layer I), a 20 mm RASAL (layer II), and a 50 mm cement concrete layer (layer III). Three types of penetrating crack were designed (i.e., the middle crack, the side crack, and the 45\({}^{\circ}\) inclined crack), and the width of the cracks was 5 mm [29], as shown in Figures 1 and 2.  
A 70# asphalt (marking in accordance with the Chinese standard of the Technical Specifications for Construction of Highway Asphalt Pavements (JTG F40--2017) with a penetration of 70 was used as the asphalt binder for preparation of the specimens, and its specifications provided by the manufacturer are listed in Table 1. Limestone was used as the aggregate. The ratio of binder to aggregate was 8.1%  
Figure 1: Specimens of three types of crack with a stress-absorption layer (in mm).  
Figure 2: Specimens of three types of crack without a stress-absorption layer (in mm).  
by weight. The continuous aggregate gradation, having the nominal maximum size of 9.5 mm, is listed in Table 2. An additional 1% activated rubber crumb and 0.7% TCA additive (percentage of the mass of asphalt mixture) was added during the blending process.  
1. To set the pre-crack, a board was placed in the test mold, and then the cement concrete was poured into the mold and flattened.
2. The mixed asphalt mixture was poured into the cement concrete rutting boards and compaction was performed.
3. The composite board was cut into specimens.  
The prepared specimens with the middle crack are shown in Figure 3.  
To accurately evaluate the crack resistance of HVASAL and RASAL, and investigate the propagation mechanism of the three types of crack, three-point bending failure tests and three-point bending fatigue performance tests were designed. Three-point bending failure tests were conducted to obtain the needed parameters for the three-point bending fatigue tests. Because of the thinness of the structure layer and the stress-absorption layer studied, the force control mode is closer to the actual stress state of the asphalt mixture in the pavement, so it can better explain the fatigue characteristics of the high viscosity asphalt [11]. Hence, the force-controlled loading mode was adopted for the three-point bending fatigue tests. For both the failure and the fatigue tests, the test temperature was set at 15 \({}^{\circ}\)C, the loading mode was the intermediate loading, the distance between the two ends was 250 mm, and the pressure head rate of the test machine was 2 mm/min, as shown in Figure 4. The ultimate load of the specimen was obtained by the three-point bending failure test. Forty percent of the ultimate load was used as the load for the three-point bending fatigue test.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Properties** & **Standard** & **Value** \\ \hline Penetration (25 \({}^{\circ}\)C, 100 g, 5 s) & T0604\(-\)2011 & 70 (0.1 mm) \\ Softening point & T0606\(-\)2011 & 47 (\({}^{\circ}\)C) \\ Viscosity (177 \({}^{\circ}\)C) & T0625\(-\)2011 & 3.8 (Pa\(\cdot\)s) \\ Elastic recovery (25 \({}^{\circ}\)C) & T0662\(-\)2011 & 72 (\%) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Properties of asphalt.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sieve size (mm)** & 9.5 & 4.75 & 2.36 & 1.18 & 0.6 & 0.3 & 0.15 & 0.075 \\ \hline
**Passing percentage** & 100 & 80.4 & 45. & 35.3 & 22.2 & 17.3 & 12.4 & 7.6 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Aggregate gradation.  
Figure 3: Molded piece and finished specimen.