# A Review of Long-Term Skid Resistance of Asphalt Pavement
## 3 Skid Resistance Mechanism and Influencing Factors of
### Effect of Aggregate Properties on Skid Resistance of Asphalt Pavement  
Aggregate is one of the most important materials in AP, and its physical and mechanical properties are key factors affecting the performance of AP, which has an important impact on the skeleton structure of AP but also determines the rutting resistance of AP and anti-fatigue performance, so the selection of high-quality aggregates can ensure that AP has a better road performance and skid resistance [84; 85]. Micro-texture and aggregate size play significant roles in affecting the initial and long-term skid resistance of asphalt pavements. Micro-texture can provide additional frictional surfaces. When vehicle tires come into contact with the pavement, the micro-texture can embed into the grooves on the tire surface, enhancing the mechanical interlocking between them, thereby improving the initial skid resistance of the pavement. During long-term use, although the micro-texture will gradually wear away, if the pavement material possesses a certain self-healing ability or can continuously expose new micro-textures under traffic loads, the skid resistance can be maintained to some extent. Larger-sized aggregates can make the pavement surface rougher, increasing the contact area and friction force between the tires and the pavement, thus enhancing the initial skid resistance. Moreover, under the long-term action of vehicle loads, they can more effectively resist wear, preserving the roughness and skid resistance of the pavement. Meanwhile, appropriately sized aggregates can interlock with each other in the pavement, forming a stable structure that can withstand the repeated action of vehicle loads, making it less likely for aggregates to become loose or fall off, which is conducive to maintaining long-term skid resistance [86; 87]. A schematic diagram of aggregate pavement abrasion is shown in Figure 6.  
It has been shown that coarse aggregates with rough surfaces can be embedded with each other to form a large internal friction angle after rolling, and the resulting AP has better skid resistance and shear resistance compared to the mixture combined with aggregates with smooth surfaces [88]. Aggregate abrasion resistance is usually reflected by the abrasion value [89]. A high abrasion value of the stone can maintain its rough microstructure for a long time, which can increase the degree of occlusion between the road surface and tires to enhance the skidding resistance of the road surface [90; 91]. Coarse aggregates with lower hardness and poor abrasion resistance, although they can form a rougher surface in the early stage of pavement construction, will soon have their original rough surface ground by the continuous rolling and abrasion of traveling vehicles. This cannot guarantee the safety of traveling [92]. The aggregate abrasion value is the evaluation of stone material resistance to friction, impact, and shear and other comprehensive roles of the performance indicators; the larger the abrasion value of the aggregate, the more likely it is to be abraded, and vice versa [93]. The crushing value of aggregate is an index to evaluate the performance of stone material to resist crushing; pavement aggregate is subject to the combined action of friction, impact, and crushing of tires for a long period of time. To maintain a high level of skid resistance, it is required that the aggregate does not wear out too much and crushes too much under the action of tires [94]. In addition, the abrasive value of the aggregate has the greatest degree of influence on the skid resistance of AP, i.e., the higher the abrasive value of the aggregate, the better the skid resistance, and the nature and percentage of coarse aggregate have a more significant influence on the skid resistance of AP [95; 96].