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Spray tanker surface dressing a road

Surface Dressing

Surface Dressing is a long established proven highway maintenance technique. In simple terms it involves the even spray application of an emulsion bituminous binder through a purpose built spray tanker onto the existing road surface followed immediately by the even application of aggregate chippings to ‘dress' the binder. Surface dressing offers many advantages;

  • Seals the road surface against ingress of water which is known to be one of the major causes of asphalt pavement deterioration.
  • Arrests the deterioration of the road surface and underlying road pavement structure.
  • Restores the necessary level of skid resistance to the road surface with the resultant benefits of reduction in skid related traffic accidents.
  • Timely intervention will enable worn out road surfaces to last longer thereby increasing the time to when structural maintenance is required.
  • Can help to reduce spray caused by vehicles travelling on wet road surfaces.
  • Maximises the cost effectiveness of limited highway maintenance funds.

When to Surface Dress

  • Before the road surface deteriorates to the stage at which expensive major patching and/or reconstruction is required.
  • Before surface skidding levels fall below the nationally accepted intervention level for the class of road in question.

  • Cost effectiveness

  • Low initial cost - in the region of £1.20 m2 for routine single dressings to £2.50 m2 for specialist multi-layer dressings for high speed roads.
  • Low cost/life index. When done properly, at the right time, surface dressing is a very cost effective treatment.
  • The product can be likened to painting one's house. It needs doing before deterioration occurs and means that expensive preparation or replacement is not required.

Which roads can be Surface Dressed?

  • All classes of road, from single track, unclassified roads and footpaths to national high speed motorways can and have been successfully treated.

Some important considerations

  • Surface Dressing can be specified in accordance with The Specification for Highway Works Clauses 919 (recipe) and 922 (performance design).
  • The dressing required must be designed for the conditions of the road surface on which it is to be laid and the traffic expected on it. The latest version of Road Note 39 gives guidance on all aspects of design. The RSTA run regular training courses on surface dressing covering tuition on design.
  • The work should be carried out by a fully experienced contractor who can demonstrate that he has a record of quality work. All RSTA surface dressing member companies are accredited to ISO 9001 Quality Standard and most have achieved accreditation to the QA National Sector Scheme No 13a - Surface Dressing. Clients are urged to specify such quality accreditation requirements in their Contract Documents.
  • Surface dressing binder technology has developed enormously over the last 20 years or so. It is important to specify the binder quality required to give the optimum end product. Failures will be minimised by the proper binder selection.
  • Proper "aftercare" is essential. This, together with the correct design and binder specification, will minimise any loose chipping problem.
  • The Code of Practice on Surface Dressing available from RSTA covers every aspect of the process and should be regarded as representing best practice. There is also a joint CSS/RSTA Code of Practice on Traffic Management and Signage relating to Surface Dressing works.

Environmental considerations

  • Surface dressing minimises the use of scarce national aggregate resources - Most of the aggregate used is in direct contact with the vehicle tyre, not buried below the road surface.
  • Accident levels will be reduced by restoring adequate skid resistance.
  • By careful design ‘quiet' surface dressings can be installed to reduce road noise generated by traffic.
  • The rapid speed of the process means that disruption to road uses, local businesses and emergency services is minimised.
  • Compared to re-laying hotmix asphalt, surface dressing provides a very low carbon footprint solution typically at least 4 times less embodied carbon compared to asphalt.

Life expectancy

  • Proper attention to design and execution has provided surface dressing lifetimes well in excess of 10 years, even on very heavily trafficked sites.

Summary

  • Surface dressing is an established, proven process. It is an extremely cost-effective surface maintenance treatment when properly designed, specified and executed.
  • Developments in surface dressing materials, techniques and equipment and improved operator training mean the risk of failure has been significantly reduced.
  • Surface Dressing helps over stretched highway budgets stretch even further.