Effect of surface macrotexture on skid resistance measurements by the British pendulum test

Abstract

The British pendulum test is a common procedure for laboratory as well as field measurement of the low-speed friction of a road surface material. It is widely suggested that the measured low-speed friction is largely governed by the surface microtexture of the road material, and many researchers and practitioners have considered the friction measurements made by the British pendulum test to be an indirect form of measurement of available microtexture of the road material. The experimental results presented in this paper show that this general view is not always correct. This study investigated the effects of test surface macrotexture represented by the following two geometric parameters: the size of subcontact areas and the magnitude of gaps between subcontact areas. The test results demonstrated that the low-speed friction measurements by the British pendulum tester were significantly affected by test surface macrotexture. This finding also implies that the closely packed aggregate condition required for the laboratory British pendulum test may not produce a correct assessment of the skid resistance of the true road surface. Laboratory measurements are likely to overestimate the skid resistance of a road surface if the surface aggregate spacing is wider than the spacing of the manually-packed laboratory specimens.