A comparison study of friction measurements for chip seal

This paper presents a development in measuring skid resistance in a laboratory performance test for chip seal. It is important to develop a relationship between the British pendulum test (BPT) and the locked-wheel skid test (LWST), or grip tester (GT). The chip seal is a typical pavement preservation treatment used by the North Carolina Dept. of Transportation (NCDOT). In North America, loss of skid resistance is a common road condition that indicates the need for a chip seal, as one of the major advantages of chip seal is an increase in skid resistance. Most agencies have a specified cycle in which skid resistance is measured as a part of their pavement-management system. These skid resistance measurements are invaluable when deciding which roads require chip seal [Gransberg, D. D. and James, D. M. B., "Chip Seal Best Practices," NCHRP Synthesis of Highway Practice 342, Transportation Research Board of the National Academies, Washington, D.C., 2005]. In this study, skid resistance was evaluated on 14 selected chip seals using three different tests: the BPT, LWST, and GT. The correlation between British pendulum number (BPN) and skid number (SN) was relatively strong with an R2 value of 0.74. This finding indicated that the BPN measured in the laboratory could be utilized for predicting the SN, which cannot be measured in the laboratory.