Research undertaken between 2007 and 2009 examined the influence of binder rise in reducing tyre–road friction of chipseal surfaces. The emphasis was on the most extreme form of binder rise when the binder is level or above the sealing chip resulting in the formation of a black, slick surface. This condition is referred to as flushing.
The research involved performing texture profile and friction measurements on chipseal surfaced public roads. Both locked-wheel braking with an instrumented vehicle and the dynamic friction tester were employed for the friction measurements.
The key finding was that the presence of flushing in chipseal surfaces reduced tyre–road friction by about 20% to25% under both wet and dry conditions. Therefore, a robust means of identifying the presence, degree and extent of binder rise in chipseal road surfaces will be beneficial in improving the safety management of road networks. A secondary finding was that attempts to identify binder rise from texture-based statistics derived from two-dimensional road surface profiles are unlikely to be successful even for the flushing condition unless complemented with other information such as skid resistance or surface reflectance.