Changes in asphalt pavement friction components and adjustment of skid number for temperature

The results of a study aimed at investigating the effects of temperature and surface texture on the friction force developed at the tire-pavement interface during skidding are presented. Ten field sites representing a variety of asphalt pavements in the State of Ohio were selected for the study. Five laboratory briquettes made from the same materials used in the construction of the pavements were prepared for each of the sites. Skid resistance measurements were performed on the briquettes using a portable British pendulum tester. The friction force was considered to consist of two parts, namely, the wet adhesion and the hysteresis components. The adhesion and hysteresis components were measured separately using water and liquid hand soap as lubricants. To simulate the changes due to wear and aging of pavements, several cycles of mechanical polishing were conducted and the available contact area after polishing was determined using a digital image processing technique. Tests were conducted at five different temperatures. The hysteresis component of friction decreased with increasing temperature regardless of surface texture state. The adhesion component was more sensitive to surface texture effects. Hysteresis was found to account for the larger part of the total friction force. Combined friction decreased with increasing temperature on a polished surface; hence it is recommended that skid numbers obtained at any arbitrary temperature be normalized with respect to a value at a reference temperature, for example, 293 K (68 degrees F).