# Evaluation of Anti-Skid Performance of Asphalt Mixture Based on Accelerated Loading Test
## 3 Result and Discussion
### Texture Depth Test
Figure 8a reveals that S1 and S4 have the largest initial pendulum values among the tested schemes. While the gradation curves of S1, S2, S3, S5, and S6 are similar, the gradation of S4 is finer. As the test pieces were prepared using the same molding method, differences in pendulum value can be attributed to independent factors such as the rolling process. S1 has a lower oil-stone ratio than S2, resulting in a higher initial pendulum value. Conversely, an increased oil-stone ratio in S3 reduced the initial pendulum value. The thinner gradation of S4 increased its initial pendulum value, which could be related to a thinner oil film resulting from gradation thinning. S5 and S6 are andesite and limestone aggregates, respectively. They exhibited no significant difference in the initial pendulum value compared to S2, suggesting that aggregate lithology has a minimal impact on the initial pendulum value. As the number of accelerated loading times increased, the pendulum values of the six anti-skid surface layers of AC-16 gradually decreased. A rapid decay state is observed in the pendulum values before loading 5000 times, which is attributed to the initial rapid wear of the spikes and bumps of the road surface by the loading wheel, leading to faster decay of the friction coefficient BPN. From 10,000 to 400,000 loading times, the pendulum value of each AC-16 scheme stabilized during attenuation. This is due to the wear of the bumps and spikes of the anti-skid road surface, which stabilizes the anti-skid performance of the road surface, which is mainly determined by the micro-texture of the aggregate. The friction coefficient of the road surface remains stable. After being loaded 400,000 times, the friction coefficient of AC-16 is stable as the texture of the road surface is worn to a certain extent and the macro and microtextures of the road surface reach a stable state. Upon conducting the 600,000-time loading test, it was observed that the final pendulum values of S1, S2, and S3 are relatively consistent, implying that the oil-stone ratio's impact on the pendulum value is negligible. The fine gradation of S4, as compared to S2, results in a smaller final pendulum value. The andesite aggregate in S5 yields the highest final pendulum value among all schemes, while the limestone aggregate in S6 yields the lowest. Previous research indicates that the mechanical properties of coarse aggregate (i.e., polishing value, crushing value, and abrasion value) play a decisive role in the durability of asphalt pavement's anti-skid properties. Comparatively, the coarse aggregate used in S5 exhibits a slightly larger polishing value, smaller crushing value, and abrasion value than S3 and a greater pendulum friction coefficient after stabilization than S2. On the other hand, the pendulum friction coefficient of S6 after stabilization is less than that of S2, which can be attributed to the limestone aggregate's low wear resistance and angularity compared to the diabase aggregate in S2. Hence, this study validates that aggregate properties significantly influence the AC-16 asphalt mixture's anti-skid durability. Figure 8b presents the analysis of the impact of the oil-stone ratio and aggregate gradation on the initial pendulum value of six AC-16 schemes, namely S7, S8, S9, S10, S11, and S12. Schemes S7, S8, and S9 have identical gradation curves but different oil-stone ratios. An increase in the oil-stone ratio is found to be associated with a decrease in the initial pendulum value. Scheme S10 has a relatively thicker gradation compared to S7, leading to a decrease in the initial pendulum value. This finding suggests that a thicker gradation is linked with a smaller initial friction coefficient under the same oil-stone ratio. Scheme S11 has the same gradation as S7 but uses coarse andesite aggregate. There is no significant difference in the initial pendulum value between the two, indicating that the lithology of the aggregate has a negligible effect on the initial pendulum value of the AC-type asphalt mixture.