## 2 Research on Anti-Skid Mechanisms of Asphalt Pavement  
### Mechanical Mechanism Between Types and Road Surfaces  
#### 2.1.1 Van Der Waals Forces Between Types and Road Surfaces  
The skid resistance of the road surface is defined as the resistance generated by the sliding of tyres on the road surface when a moving vehicle is subjected to braking [5]. When a vehicle is driven normally, the rubber molecules of the tyre and the road surface molecules are in very close proximity resulting in the weak attraction generated by transient charge polarisation, which directly affects the anti-skid performance [6]. In 1963, [PERSON] et al. [7] conducted a pertinent study on the interaction force between the tyre and the road surface. They proposed that the adhesion force between the tyre and the road surface can be attributed primarily to the adhesion force and hysteresis force. The road surface adhesion force can be expressed by Equations (1) and (2). From the perspective of the tyre-road contact area, the contact area can be divided into an adhesion area and a sliding area. But [PERSON] et al. [8] considered that friction (adhesion) has three components: attachment, hysteresis, and ploughing. As shown in Figure 1, with increasing slip rate, the shear stress within the tyre contact patch continues to increase, and when the elastic deformation limit of the rubber molecular chain is exceeded, the adhesion region is forced to shift to the sliding region (macroslip), resulting in the expansion of the sliding region and the contraction of the adhesion region. The maximum friction factor may occur at any point in the contact region while the vehicle is moving, particularly when the slip rate is between 7% and 25%. Therefore, for the analysis of tyre-road contact, the tyre-road adhesion characteristics rather than friction characteristics should be considered. [PERSON] and [PERSON] et al. [9; 10; 11; 12] investigated the Van der Waals forces between tyres and rough road surfaces. [PERSON] concluded that the adhesion between the road surface and the tyre results from shear action on the contact surface, especially on smooth, clean surfaces. The hysteresis force is correlated with the attenuation of rubber damping energy. The vehicle brakes most effectively when the longitudinal adhesion force reaches its peak. When the tyre is in partial slip, the tyre experiences an elastic slip phenomenon, where the slip area expands to cover the entire contact area. The friction applied to the tyre is known as the limiting adhesion force, and its magnitude is equal to the friction when the entire contact area is sliding. At this point, [PERSON]'s law no longer applies. The tyre-pavement contact region is divided into two distinct domains: an adhesion domain and a sliding domain. In road engineering, a friction factor is typically used to quantify the Van der Waals forces between the road surface and the tyre [13]. Friction factors can be classified as either rolling or sliding, depending on the state of vehicle motion and braking. The friction factor is influenced by various factors, including the characteristics of the road surface, the performance of the tyre, the operating parameters of the vehicle, and environmental factors [13; 14].  
\[F_{a}=\sum_{i=1}^{n}\tau_{i}\times A_{i}=\sum_{i=1}^{n}\varphi\times\sigma_{i} \times A_{i} \tag{1}\]  
\[F_{\rm h}=c\sum_{i=1}^{n}(E_{c_{i}}-E_{e_{i}}) \tag{2}\]  
where \(F_{a}\) is the adhesion force, \(F_{\rm h}\) the drag force of the tyre, \(\tau_{\rm i}\) is the interfacial shear strength, \(n\) is the effective number of micro-bumps, \(\varphi\) is the adhesion coefficient between the tyre and the road surface, \(\sigma_{\rm i}\) is the normal contact stress on the surface of the first \(i\) microbump, \(c\) is the constant of proportionality, and \(E_{\rm c}-E_{\rm e}\) is the tyre energy loss on the surface of a single micro-bump.  
Figure 1: Adhesion coefficients under different slip ratios of tyre.