Influence of Thin Water Film on Asphalt Pavement Skid Resistance: from Indoor to In-Situ Test

Pavements skid resistance, especially in wet states, is an essential indicators of traffic safety. However, the existing testers cannot reflect actual road friction situations and oversimplify water’s effect on texture and skid resistance. Therefore, this study compared a traditional British pendulum tester (BPT) with actual vehicle braking. A simplified water coverage simulation programme was proposed, and the BPT characterised the influence of different thin water films on skid resistance in the laboratory. Besides, several freshly constructed road sections (AC-13, SMA-13, and PAC-13) were tested with both BPT and vehicle braking during rainfall. The results showed that water film, even thin, is unfavourable for pavement skid resistance. The BPT results were inconsistent with that of the vehicle braking. Because the tribological properties characterised by BPT are provided by micro-texture and partly macro-texture within the rubber-texture interaction depth (0.1 mm). Larger texture depth and more tortuous and connected pores will offer pavements larger water capacity and higher water permeability, which is beneficial for alleviating braking distance reduction during rainfall. In general, an ideal skid resistance tester should consider characteristics within the rubber-texture contact depth and should consider braking conditions such as speed, water film thickness, drainage method, and slip rate.