High-speed measurement of ravelling on porous asphalt

Ravelling is defined as the loss of aggregate from the surface layer. This loss affects the integrity of the surface layer and as the severity increases so does the chance of holes in the pavement occurring. Ravelling can influence negatively the ride quality of the pavement and may cause increased noise levels and increase the occurrence of windscreen damage caused by loose aggregate being thrown up by tyres. DWW has developed in the past few years a high-speed method, the so called Stone(a)way model, for the detection of ravelling on porous asphalt. The principle is based on the detection of missing stones by its characteristic dimensions in the texture profile measured by the 64 KHz lasers in the wheel paths of the ARAN survey vehicle. Large-scale testing showed that the repeatability of the Stoneway model is better than the repeatability of VCS. In the monitoring cycle 2002/2003 the program has been extended with the Stoneway observations. In parallel the VCS was carried out. First results of the comparison on the network level show that the good results of the large-scale test are confirmed, clearing the way for the abandoning of VCS in favour of the automated collection of ravelling data.