Research has shown that compared with open-textured coated macadam to BS 4987 an effective and durable spray-reducing surface can be obtained by increasing the viscosity of the binder and further stiffening the mix by substituting hydrated lime for part of the filler. Details are given of the performance of pervious surfacings laid at 16 experimental sites using both 10 and 20 mm aggregates. Materials with a high initial permeability can retain spray-reducing properties for at least three years under the heaviest motorway traffic. The 20mm pervious coated macadam has a longer effective life under heavy traffic. Bitumens showing a high miscibility with oil are liable to lead to early compaction and also those of a lower viscosity than 100 per should not be used. The authors describe means of overcoming problems that may occur in laying. Comparisons of surface dressing, pervious macadam and rolled asphalt given in a merit table show that pervious surfacings give the lowest spray and noise.
Abstract