The performance of open-textured macadam, pervious macadam, dense bitumen macadams, 'delugrip' surfacings and rolled asphalts as maintenance wearing-course materials and a surface dressing, were assessed from measurements of deformation, riding quality, texture depth, sideway-force coefficient, braking-force coefficient, permeability, void content, noise and spray. All the mixed materials showed adequate resistance to deformation, produced a good riding surface and provided a high level of resistance to skidding at low speeds but those materials with low texture depth showed considerable reduction in braking force coefficient at high speeds. Macadam and 'delugrip' materials produced noise levels 2-3 dba below those previously recorded on rolled asphalt and surface dressing. Spray measurements showed that pervious macadam, surface dressing and open-textured macadam promoted less spray than the other surfacings. In the more permeable materials binder hardening produced fretting and some disintegration; this resulted in only six years of road life for the dense bitumen macadams, pervious macadam and two 'delugrip' surfacings. Open-textured macadam was more durable than dense bitumen macadam, as found in previous road experiments, but rolled asphalt emerged as the most durable maintenance material. (Author/publisher)
Abstract