Bituminous Surfacing Selection
The bituminous surfacing type shall take into account the likely road users (e.g. motor vehicles, pedestrians, cyclists) and environmental factors (e.g. noise, snow clearing).
The selection of bituminous surfacing shall be undertaken in accordance with the latest version of the Austroads Guide to Pavement Technology Part 3: Pavement Surfacings.
The selection of bituminous surfacings shall be consistent with the provisions of the Tasmanian State Road Traffic Noise Management Guidelines (2011).
A waterproofing seal shall be provided underneath all asphalt wearing courses, except for dense graded asphalt greater than 100mm thick. The preferred waterproofing seal is a 10mm primerseal with bitumen emulsion.
Where an asphalt surfacing is proposed, asphalt fatigue shall be assessed in accordance with the Austroads Guide to Pavement Technology series.
Open Graded Asphalt (OGA) shall only be used to address specific issues. OGA shall not be used in locations where there are significant stopping and turning movements such as at intersections with traffic lights, approaches to roundabouts etc. Their use is limited to where:
- The substrate is free of depressions that will cause water to pond
- Water is free to drain from the edge of the OGA
- The OGA is placed on an effectively impermeable surface.
- Class 170 bitumen shall be used in sprayed seals and in most conventional asphalt applications. Class 320 bitumen may be used for specific applications such as deep lift asphalt pavements or to provide increased rut resistance. For sites with significant heavy vehicles generating additional stress for the surfacing, the designer shall consult with Department of State Growth Road Asset Management Section.
If a polymer modified binder treatment is specified, consideration must be given to the availability in Tasmania of the various binders.
Traffic shall not be allowed to travel on sprayed seals with aggregates larger than 14mm nominal size.
Traffic shall not be allowed to travel on primes or tack coats.
Primerseals are a short term treatment. Specification of the primer seal shall take into account the design requirements of the final seal. The typical stone size allowable for primersealing is 10mm. Approval is required from Department of State Growth’s Road Asset Management Section if specifying an alternate stone size for a primerseal.
For pavements constructed clear of traffic with delayed opening time, particularly attention to the surfacing design is required. The key factors are the time of initial seal, and time lapse until the road is open to traffic.
All bituminous surfacing selections shall be approved by Department of State Growth Road Asset Management section.