When the surface of a road ages the bitumen becomes brittle and cracks. Cracks allow water to get in under the road and undermine the surface, leading to potholes and damaging the expensive pavement below the surface. Most resurfacing is preventative to stop water damage before it occurs and avoid the cost of extensive repairs to the pavement.
Council has an annual program of road resurfacing to preserve the pavement assets in the most effective manner across the city within budget constraints. There are many surfacing treatments available. The three most common types of surfacing performed are:
- Asphalt – a bitumen-based concrete-like mixture of stone and bitumen laid at 30mm thickness or greater.
- Rejuvenation products – water-based bitumen rejuvenation agent is applied to the surface of the road by a pressure spray system.
- Sprayed seals – a film of bitumen sprayed on the road and covered with aggregate.
Treatments are selected depending on the condition of the existing pavement, the road function and the traffic volumes.
Spray seals are used on low volume streets over existing asphalt surfaces to extend their life. Where there is the presence of heavy vehicles or areas of high stress on the road pavement, such as in intersections, asphalt may be used as the resurfacing treatment. Asphalt treatments are expensive and only used where spray seal treatment may not be suitable. The most effective resurfacing treatment has been selected for your street to preserve the City’s pavement assets.
Your street has probably been spray sealed. This requires coverage of aggregate to be laid over a film of bitumen to provide a hard wearing, skid resistant surface. In order to ensure all the bitumen is covered, a little more aggregate is placed than may actually stick to the surface.
This aggregate is left on the surface for up to three days before being swept off. The loose aggregate gets moved around during this time because of traffic and may collect on the road or in gutters giving the appearance of piles of aggregate. This aggregate is then removed and is recycled. Loose aggregate is a temporary issue only and will be swept from the roadway. Council will generally sweep the street up to three times in the initial settling-in period of four weeks.
Streets that have been spray sealed before will normally be resurfaced with another sprayed seal. The original seal may have become worn and the aggregate may have become polished by traffic, giving the appearance of a smoother road. Resealing renews the texture in the road that would have been there originally. The new seal will also get smoother over time.
Spray seals provide a cost effective flexible layer over existing road surfaces or new pavements. This treatment involves spraying a film of bitumen across the road surface to seal minor cracking. The majority of Council’s spray seals contain recycled car tyres to improve flexibility and reduce cracking.
Bitumen based treatments are also known as flexible pavements because they can move and spring back under stress without cracking. This is essential to prevent traffic damage, to prevent water undermining the road pavement and provide a long road life. Bitumen surfaces are mostly recyclable and repairable and therefore more economical to maintain. Approximately 90 per cent of Australia’s sealed road network area is surfaced with sprayed seals, with the majority of the remainder being asphalt.
The film of bitumen sprayed during the spray sealing process needs to cure after the aggregate is spread and rolled. During warm weather a new spray seal is susceptible to scuffing. Scuffing occurs when vehicles back out from driveways and turn the power steering whilst stationary. If this occurs on warm days, the aggregate under the car tyres can turn over in its place, exposing a thin film of bitumen on top of the aggregate. This can be avoided by not turning the steering wheel while the car is stationary.
The bitumen film and loose aggregate can be sticky on warm days. Scuffmarks are not normally damaging to the seal and they are not a defect in the seal, they are an unwelcome but expected result of traffic movements on this type of surface. These marks become less frequent as the bitumen cures and they will eventually stop occurring.
The surface colour of an existing road may change. The colour change generally relates to the colour of the aggregate which is placed over the surface. The colour varies depending on aggregates available at the time. Some discolouration is expected over time from vehicle movements.
The cost of maintenance works such as these are based on time to complete the works. Allowing our contractors full and unhindered access to your street will ensure their time is used efficiently and that cost and inconvenience is minimised. This type of work occurs only once every fifteen years or so and is necessary to maintain the local road network for the benefits of all residents and road users.
Prior to spray sealing Council staff and contractors undertake maintenance works to ensure the sprayed seal is successful in protecting and extending the life of the road pavement. This can occur on several different occasions depending on type of works, resources and machinery required.
Typical maintenance works involve some or all of the following:
- Asphalt patching - replacement of a section of asphalt surface
- Crack sealing - sealing with rubber around road patches or repairs to prevent water penetration into underlying pavements
- Drainage pits - repair or replacement of damaged, broken or old grates
- Heavy patching - repair of small areas of damaged road pavement
- Kerb and gutter repairs - patching or replacement of broken or damaged kerbs to prevent water penetration into underlying pavements
- Subsoil drainage - installation of below-ground drainage to intercept seepage flows to protect the road pavement and seal from water damage
- Sweeping - removal of debris and sediment from gutter to prevent contamination of the seal
- Weed removal - general weeding from gutter to prevent contamination of the seal.