## 2 Materials and Test Method  
### Preparation of Asphal Mixture  
In this paper, three types of asphalt mixtures, namely asphalt concrete (AC), stone mastic asphalt (SMA), and open-graded friction course (OGFC), were selected for pavement texture characterization. Because of the influence of the maximum nominal particle size on pavement structure, three distinct maximum nominal particle sizes were employed. The AC-13, AC-16, and AC-25 asphalt mixtures with maximum nominal particle sizes of 13.2, 16, and 26.5 mm, respectively, were designed. For the AC mixture, three different nominal maximum aggregate sizes (NMASs) were utilized (AC-13, AC-16, and AC-25), while SMA and OGFC used one NMAS each (SMA-13 and OGFC-13). Figure 2 shows the grading curves for the five different types of mixtures.  
In the laboratory, various compaction methods were employed to prepare asphalt concrete specimens, including Marshall compaction, wheel-grind compaction, and Super-pave gyratory compaction. Each method possessed distinct compaction characteristics attributed to their specific mold design and loading mode [35]. The Marshall compaction employs the impact force to compact specimens, whereas the wheel-grind compaction and Superpave gyratory compact utilize kneading forces to form specimens. Among these methods, the kneading compaction method exhibits a closer resemblance to the actual conditions of asphalt pavement construction on site. Although the Superpave gyratory compactor can better replicate the field compaction state, it was observed that asphalt mixtures compacted using this method exhibited higher texture levels compared to field-constructed pavements [36]. Empirical evidence has shown that the laboratory wheel-grind compaction method closely simulates the field construction state in terms of surface texture [37]. Therefore, the present study selected the laboratory wheel-grind compaction method as it resembled best with the field conditions.  
Figure 1: Methodology outline.  
A wheel-grind compaction process was adopted for laboratory experiments, which was similar to the field compaction method. A 300 N/cm line-loaded asphalt slab roller compact was used for compacting with 12 back-and-forth runs, as shown in Figure 3a. In order to obtain an even mixture of asphalt, the mixture was heated at 155\({}^{\circ}\)C. Subsequently, the mixtures were subjected to a two-hour aging process at a temperature of 145 \({}^{\circ}\)C to simulate the transportation conditions experienced in the field. Finally, the compacting process was carried out using the wheel-grind method at a temperature of 150 \({}^{\circ}\)C. Furthermore, the asphalt-aggregate ratio of AC-13, AC-16, AC-25, SMA-13, and OGFC-13 was 4.4%, 4.5%, 3.7%, 6.1%, and 5.4%, respectively.  
The dimensions of the test pieces for each type of asphalt mixture were 300 mm \(\times\) 300 mm \(\times\) 50 mm. Each slab was divided into nine parts corresponding to the scanning region of the instrument to measure texture cloud point data accurately, as shown in Figure 3b. The texture cloud point measurement method used in this study employed  
Figure 3: (**a**) Laboratory compaction with wheel-grind method. (**b**) Asphal mixture slabs with 300 mm \(\times\) 300 mm \(\times\) 50 mm, then divided into 9 parts.  
Figure 2: Grading curves for five asphalt mixtures.  
a laser scanner. It is a non-contact method and measures the surface at a fixed distance and angle.  
Texture data were collected at various stages of the compaction process. Specifically, texture data were collected after every two rounds of the roller. The rounds used were 12, 14, 16, 18, 20, 22, and 24. In addition, the compaction of the slabs was detected using a density meter. The data collected from this measurement process were used to generate the compaction curve of the mixture as shown in Figure 4. The compaction curve can determine whether the compaction process is proceeding as intended.