Understanding Road Repairs

Understanding Road Repairs


Why are some roads in poor condition?

Like most structures, road pavements have a defined life and eventually need to be replaced. Due to the load from traffic over time, the pavement materials weaken and can no longer support the traffic. Water infiltrating the pavement can also cause it to lose strength. This weakening causes the road surface to deform (no longer a flat, even surface), cracks appear in the surface and potholes start to form.

The cost to rebuild all the pavements that have reached this point is more than is available in Council’s annual budget, so it will take many years to fix all the roads.

Council regularly undertakes condition assessments of the roads and data collected is used to determine which roads are programed for repair. The ‘worst’ road is not always selected for replacement. Often intervening on a road nearing failure can be more economic to repair, as the existing pavement materials can be salvaged, strengthened and reused. This is much more cost effective than fixing a road where the pavement material cannot be salvaged and needs to be entirely replaced. Also, higher volume roads are given priority over local residential  roads.

Why are pothole repairs and other patching necessary?

To keep the road network trafficable, Council crews undertake reactive maintenance repairs to fix defects in the pavement, like potholes. Potholes form when water infiltrates the road surface and the bitumen seal lifts under the action of vehicles driving over. That is why they commonly appear during wet weather. The repeated wheel movements remove more and more gravel making the hole deeper and dangerous.

To remove this hazard, the hole is filled with ‘cold mix’, which is a bitumen based product specifically designed for this purpose. Pothole repairs are necessary to remove the hazard until a more permanent repair can be arranged. With many roads requiring rebuilding, ongoing pothole repairs are sometimes the only viable repair method and the process may need to be repeated numerous times to keep the road trafficable until the pavement is replaced.

Another repair method is a called a ‘heavy patch’. This is where a small section (say 5m x 5m or larger) of the road is rebuilt to remove a localised defect. This repair method is used when surrounding pavement is in otherwise good condition. Heavy patching does require more resources and planning than a pothole repair. So, the pothole repair may be implemented initially to manage the hazard while the heavy patch can be designed and programmed.  

Heavy patching is a longer term repair method than pothole repairs and is appropriate when the road is in otherwise good condition. It is more expensive than pot hole repairs, so work crews need to be selective on where and how this type of patching is done.

Did you know Council undertakes a Road Resealing Program every year?

Council’s preventive maintenance program helps roads reach their intended life span. The bitumen surface becomes brittle over time, which can lead to cracking that allows water to penetrate in the pavement gravel and soils below. Each year Council undertakes a resurfacing program to rejuvenate the bitumen before it starts to fail.

This is why it may look like we are resurfacing a road that appears to be in otherwise good condition.

How are roads rebuilt?

Road pavements are made up of three main elements:

  1. wearing surface or bitumen layer;
  2. pavement materials; and
  3. subgrade or underlying soils.

These three elements act together to create a structure that supports the traffic. Engineers consider a number of factors when designing a road pavement including the traffic volume, the type of traffic, available materials and strength of the natural soils to support the weight of the traffic.

A common method to rebuild roads is to incorporate additives to the pavement to strengthen the material. This is called stabilisation. New aggregates for pavements is expensive, so strengthening the existing material in this way, not only saves money from not having to buy new materials, there is also reduced waste disposal costs.  

New aggregates will be used for the top layer of the new road.  The road is then sealed with bitumen or asphaltic concrete. If using bitumen, it is common practice to place a first coat, known as a prime seal when the works are first completed. A second coat is then added 6 to 12 months later.

Rebuilding roads does take a number of weeks. All effort is made to minimise the disruption, but unfortunately motorists will be inconvenienced.

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