# Evaluation of Anti-Skid Performance of Asphalt Mixture Based on Accelerated Loading Test
## 3 Result and Discussion
### Texture Depth Test
Moreover, the rate of MTD decay of the anti-skid surface layer was determined by the polishing value and abrasion loss of the coarse aggregate under the same wheel load. The greater polishing value of the aggregate resulted in lower Los Angeles abrasion loss and a slower MTD decay rate of the anti-skid surface layer. Figure 7 presents scanning electron microscope photographs of three types of aggregates, with andesite and diabase aggregates exhibiting rough and angular surfaces with embedding solid capacities. In contrast, the surface of limestone was pomegranate-shaped, with relatively weak embedding capacity and inferior anti-skid performance compared to diabase and andesite aggregates. The observations based on Figures 5b and 6b and Table 4 are presented as follows: The macrostructure depth of S7, S8, and S9 decreases with an increase in the oil-stone ratio. When the oil-stone ratio is the same, the pass rate of the 9.5 mm sieve in S10 is reduced from 57.2% to 53.1%, and the gradation becomes coarser, leading to a significantly larger initial value of the macrostructure depth for S4 than for S7. This demonstrates that for SMA-13, a coarser gradation leads to an increased macrostructure depth. S11, an SMA-13 mixture made of andesite aggregate, has a significantly greater initial texture depth than diabase aggregate-based mixtures with the same gradation. S12 is an SMA-10 mixture with a reduced nominal maximum particle size, resulting in a significantly decreased initial value of macrostructure depth compared to S7. The observed structural behavior of six different SMA anti-skid surfaces under increasing loading cycles is investigated in this study. Contrary to the gradual reduction in MTD observed in AC-16, the structural depth of the six SMA anti-skid surfaces shows a wave-shaped variation with loading cycles, as depicted in Figure 5b. Specifically, the structural depth of S7, S8, S10, and S11 exhibits a decreasing trend before 50,000 to 100,000 loading cycles, followed by a slight upward trend. Subsequently, between 300,000 and 500,000 loading cycles, a decline in the structure depth is observed. This complex behavior is attributed to the relatively thick oil film in the SMA asphalt mixture that induces compaction during the initial loading stage, resulting in a decrease in the texture depth. However, with the action of the loaded tire and water erosion, the asphalt mortar between the surface of the SMA asphalt mixture and the aggregate gap will fall off, leading to an increase in the depth of its macroscopic structure. Based on the results obtained after 600,000 loading cycles, the mean texture depth (MTD) attenuation rate was studied for various SMA anti-skid surfaces. S11, which utilized andesite aggregate, exhibited the highest attenuation rate of MTD, while S12 (SMA-10) had the smallest attenuation rate, followed by S8. This observation is attributed to the smaller nominal particle size and initial structural depth of S12, which resulted in a lower attenuation rate of its structural depth. For the SMA-13 anti-skid surface layer that employed diabase aggregate, S8 (oil-stone ratio of 6.0%) had the lowest attenuation rate of structural depth, followed by S10 (coarser gradation). These findings underscore the importance of employing a reasonable oil-stone ratio and coarser gradation to minimize the attenuation of macrostructure depth. Following 600,000 load cycles, the mean attenuation rate for the macrostructure depth was determined to be 20.6% for the six groups of AC-16 and 9.3% for the six groups of SMA. The results suggest that the SMA asphalt mixture performed better than the AC asphalt mixture, as indicated by the attenuation rate index. Figure 7: Scanning electron microscope photos of three kinds of aggregates (5000\(\times\)). The microstructure of a road surface can be characterized by its pendulum value, which is positively correlated with the pendulum friction coefficient and thus indicates better anti-skid performance.