A statistically designed on-road measurement programme was undertaken to identify the cause of poor wet skid resistance performance of chip seal surfaces in the Hawke's Bay region of New Zealand. Twenty four sites located on straight sections of State Highways 2 and 50 were selected to contrast differences between high and low texture depth, percent crushed faces of the sealing chip, and commercial vehicle volumes. In every case, the chip seal surface was constructed from alluvial sourced grey wacke aggregates having a nominal polished stone value (PSV) of 54. Measurements at each site comprised skid resistance by SCRIM and GripTester, macrotexture by laser profiling technique and volumetric patch method, and drainage ability by outflow meter. These measurements clearly demonstrated that for aggregates with a given PSV, gains in wet skid resistance are possible through paying particular attention to macrotexture geometry with respect to wavelength and slope characteristics of the sealing chips. The critical wavelengths identified were between 1-5 mm, influencing hysteresis in the tyre rubber, and 30-40 mm, influencing drainage. The principal finding was that the crushing process can beneficially affect the skid resistance provided by alluvial aggregates through increasing texture in the 1-5 mm wavelength range. (A)
Samenvatting