PREMIUM SURFACE DRESSING SYSTEMS

Current economic restraints mean that motorway and trunk roads are much more likely to be surface dressed than before. This article explains the types of systems which may be used and the reasons for choosing them. Common types of surface dressing failure such as scabbing, bleeding and fatting-up, are discussed and their causes examined. The effect of stresses imposed by the traffic, the climate and the condition of the old surface on the choice of binder is investigated. Probes to measure road hardness can be used to determine the optimum size of aggregate. The advantages of double surface dressing either by a pad coat or by double, or single spray and double chip are discussed. Two sizes of aggregate are used where the maximum size of the smaller chip is half that of the larger size. Double surface dressings are intended for and very difficult areas and for small areas of stress in the otherwise easy and average conditions. Single spray double chip (gap-graded) with an appropriate binder is an alternative where reduced maintenance is required. Double spray - double chip (gap or continuously graded) may be used with advantage at the extreme ends of the season. The curing of thermosetting binders is accelerated by high temperatures. (TRRL)