# Evaluation of Anti-Skid Performance of Asphalt Mixture Based on Accelerated Loading Test
## 4 Conclusions  
This study employed an indoor small-scale accelerated loading test to investigate the anti-skid performance of asphalt mixtures under water bath conditions. Specifically, six groups of AC-16 and six groups of SMA were tested to evaluate the impact of aggregate lithology, gradation, and asphalt dosage on anti-skid performance. The study proposed an index to evaluate the anti-skid durability of the asphalt mixture. The main findings are summarized below. 1. The initial values of the mean texture depth (MTD) and British pendulum number (BPN) of an asphalt mixture are significantly influenced by the gradation and oil-stone ratio. As the oil-stone ratio increases or the gradation becomes finer, the initial MTD value of both AC-16 and SMA-13 gradually decreases. This can be attributed to the presence of asphalt film, which limits the aggregate texture's anti-skid effect in the initial stage (bitumen masking effect). Furthermore, finer gradation is more likely to result in a higher initial friction coefficient. 2. Through an accelerated loading test, the evolution of the mean texture depth (MTD) of AC-16 and SMA-13 under water bath conditions is investigated. The MTD of AC-16 decays rapidly at first, then gradually wears down and finally reaches a stable state as the number of loading cycles increases. However, the MTD of SMA-13 exhibits a wavering trend. Analysis reveals that this phenomenon is mainly due to the slight compaction of the asphalt mixtures during the initial stage of loading, which results in a decreasing trend in the structural depth. With increasing loading cycles, the AC-16 mix enters the phase of angular surface wear, leading to a gradual decay of \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**CNAT (Million Times)** & **200** & **400** & **800** & **2000** & **3000** & **4000** \\ \hline B value & 7.0 & 6.0 & 5.1 & 4.3 & 4.1 & 3.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 13: Control standard of attenuation rate B value. MTD. Conversely, the SMA mix enters the surface asphalt mortar shedding stage, resulting in an increasing trend in its MTD. These findings provide insights into the wear behavior of asphalt mixtures under accelerated loading conditions, highlighting the role of water and tires in the evolution of the surface texture of asphalt mixtures. 3. The behavior of two asphalt mixture types, AC-16 and SMA, was investigated under accelerated loading conditions. Specifically, the evolution of the British Pendulum Number (BPN) as the loading frequency increased was analyzed. Results indicate that the BPN of AC-16 displays a biphasic decay trend, characterized by a rapid initial decay (before 20,000 cycles), a stable decay stage (20,000-400,000 cycles), and a relatively stable state thereafter. Conversely, the BPN of SMA show an initial increasing trend followed by a gradual decrease. The thickness of the asphalt film is thought to be responsible for this trend, as it initially prevents the texture from fully exerting its anti-skid effect. The combined action of the loading wheel and water causes the asphalt film to fall off, resulting in an increase in BPN. 4. This study has conducted 600,000 accelerated loading tests to investigate the impact of aggregate lithology, asphalt mixture type, and oil-stone ratio on the anti-skid durability of asphalt pavements. It has been observed that the BPN of the asphalt mixture is influenced by the aggregate's polishing value, crushing value, and abrasion value, with a larger BPN associated with a larger polishing value and smaller crushing and abrasion values. Moreover, the anti-skid index attenuation rate is lower for coarser and finer gradations. The SMA asphalt mixture shows better anti-skid performance and durability than the AC asphalt mixture. 5. A predictive equation for the attenuation of the anti-skid performance of asphalt mixtures was developed and verified. The results of the verification test demonstrated the proposed equation's high accuracy and reliability.