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Information about the work of  Orange City Council, located in the Central West of NSW

Understanding Road Repairs

To understand Orange City Council's roads strategy, this simple introduction outlines how roads are built.

A road is made up of three layers :

1. The Surface
2. The Pavement
3. The Formation
(Subgrade)

Diagram showing 3 layers of a typical road.

The ‘Surface’ of the road is the layer you travel on. It is usually made of either a Sprayed Bitumin Seal or hot-mixed Asphalt layer.

The ‘Pavement’ is what supports the road surface and is what gives the road its strength. The pavement is made up of one or more layers of gravel known as the base and sub-base. The pavement is generally 300mm to 500mm thick. The pavement can be further strengthened by adding a “binder” into the gravel during construction.

The lowest layer in a road is natural material known as subgrade. This is basically the earth beneath the pavement generally consisting of clay, ironstone and occasionally rock. The strength of the sub-grade can also be improved by adding a binder into it.

Road Maintenance (Repair) Options

Road maintenance involves the repair of small problems (pot holes) in the surface or underlying pavement, so that the road can reach its nominated life in a safe and trafficable state.

As the road gets older a number of factors will affect how much maintenance it needs. These factors include:

  • • Changes in traffic volumes and heavy vehicle use
  • • Weather patterns
  • • Changes in the water table
  • • Gravel quality and subgrade conditions
  • • Installation of underground services

Road repairs are usually tackled by ‘patching’. There are generally two main types of patching.

  • • Pot-hole Patching
  • • Heavy Patching.

1. Pot-hole Patching

This involves filling holes that have developed in a sealed road with a mixture of bitumen and stone.

There are three options of pot hole patching used by Orange City Council.

Jet-Patching: This process involves the use of the City Council’s Jet-patching truck.

The jet-patcher pumps out a mix of bitumen emulsion (a mixture of bitumen and water) and stone that is used to fill the hole. It is usually used on small to medium sized holes and doesn’t require rolling as it relies on the emulsion to “break” and bind the stone together. This technique does not generally perform well when patching in wet conditions.

Cold Mix Patching: This type of pot-hole patching involves filling holes with a mixture of emulsion, stone and sand. Compacting the material into the hole using a roller is desirable in order to compress the different sized stone and sand together.

Cold-mix patching ... Single-click to see a larger imageDepending on conditions, compaction is not always possible and the holes are sometimes filled above the road surface for passing traffic to compress.
This approach is used to patch medium to large potholes, or where the underground pavement has given way in a heavily-used wheel path.(known as a ‘shove’) Cold-mix patching performs better than jet-patching in wet conditions, but is not ideal in wet weather.

Hot-mix Patching: Hot-mix (Asphalt) patching is generally undertaken on larger areas where a portion of pavement and surface is removed and the asphalt is placed and compacted with a roller.

Hot-mix Patching ... Single-click to see larger imageAsphalt is produced by using bitumen, that’s been heated to approximately 180 degrees Celsius, added to a mixture of stone and sand and is delivered to the site hot.
As the mix cools down it hardens and forms the patch. This type of patching can be used in large to very large pot-holes (and ‘shoves’) and performs best of all patching techniques in wet conditions. It is also the most expensive and comes at a greater risk of injury to crews.

2. Heavy Patching

Heavy patching is used when large sections of the road are badly damaged or deformed. The remaining surface is removed and the pavement gravel is pulverised by Road Reclaimer machinery.

Road Reclaimer .. Single-click to see larger imagwA binder is added for strength, the pavement is watered and re-compacted before a surface seal of either asphalt or sprayed seal is applied.
It is a far more complicated and expensive type of patching and is usually only used when the road is in a very bad condition.

Road Renewal (Replacement) Options

There are two renewal options:

  • • Road re-sealing
  • • Road Renewal

Road Re-Sealing (or Surface Renewal)
Road Re-sealing happens when the road pavement is in good condition, but the surface has deteriorated to a point where it requires replacement.

It generally involves spraying hot bitumen over the existing surface, quickly tipping a layer of stone on top and rolling the stone into the bitumen.
The placement of a new asphalt layer on the road segment can also be used.

Road Renewal (Pavement Renewal)

‘Road Renewal’ happens when the road has reached the end of its life.

The most common road renewal technique that Orange City Council uses is an extension of Heavy Patching called Pavement Rehabilitation.

Road Pulveriser ... Single-click to see larger imagePavement Rehabilitation or “Stabilising” engages the same process of heavy patching, except that whole sections of the road are dealt with. Again,

  • • the remaining surface is removed and
  • • the pavement gravel is pulverised by a Road Reclaimer machine.
  • • A binder is added for strength, and the pavement is watered and re-compacted
  • • A surface seal of either asphalt or sprayed seal is applied.