Road Repair & Renewal - How & Why?

We get lots of questions about the type and scope of work we do on the region's roads. 

For example, why do we reseal what looks like a perfectly good road in one instance, and patch potholes in others? You might be wondering how we decide which roads we will repair, which to reconstruct and what it costs to undertake different road repairs and construction.

Find out how and why below. Click on the subject headings to reveal the information.


Road Structure

A road consists of several layers, each with a different purpose. The pavement is designed to spread the wheel load so that by the time it is transferred to the natural material below, the load has been reduced sufficiently to enable it to be supported. Councils generally construct roads as flexible pavements which mean they deflect slightly under wheel loads. This deflection can be up to 1mm without any detriment but greater deflections will lead to deterioration of the pavement over time in a similar manner to a piece of metal that is bent backwards and forwards continuously.  

Road Structure Diagram

The natural material below a road pavement is referred to as the subgrade. The strength of the subgrade is measured by its bearing capacity and referred to as CBR (Californian Bearing Ratio). A CBR of 2 indicates a very poor bearing capacity, say swampy ground, whereas a CBR of 10 indicates a reasonable subgrade to build a road upon. 

The first layer of the pavement is the sub-base. It is a gravel material of moderate quality but does not have the same bearing capacity as the better quality crushed rock. It is designed to spread the load from the layer above to the subgrade but is less costly than quality crushed rock.

The next layer is the base course and this consists of crushed rock with specific sizing so that it compacts to a dense layer. The rock has a specified percentage of each size stone so that it combines together to form a dense matrix. This is the most important layer in terms of spreading and transferring load.

The sub-base and base are the structural layers of a road pavement. In recent years Council has improved the quality of the gravel used in the base course by including an additive in the gravel. This additive is generally 1 to 2% by mass of the gravel and incorporates a blend of cement, lime and slag which lightly binds the gravel together.

To protect these structural layers from water penetration and from abrasion from wheels a wearing course is then applied. The wearing course is generally referred to as the seal and consists of bitumen, which is the waterproofing agent, and stone, which is essentially to prevent the bitumen being picked up by tyres. The bitumen and stone can be formed in two ways, either as a spray seal or as hotmix/asphaltic concrete.

A spray seal is essentially a spray of bitumen followed by the application of a layer of stone which is then rolled into the bitumen. Generally a surplus of stone is laid down so that it can move around and bed down. This layer is a non-structural layer as it doesn't add a great deal of strength to the pavement.

Hotmix or Asphaltic concrete is, as the term suggests, similar to concrete but the binder that holds it all together is bitumen rather than cement. As with concrete, hotmix consists of varying sizes of stone and sand designed to fit together in a dense matrix. Although this layer does add some strength to the pavement, it is generally not considered as a structural layer unless it is of substantial thickness. 

Sometimes we're asked why we don't build concrete roads.  A concrete road would last substantially longer than a bitumen road. However, the whole-of-life cost of a concrete road is significantly more expensive than a bitumen road and concrete roads in an urban environment create additional problems. For example water, telephone and electricity services to properties are regularly being renewed or upgraded and roads are excavated to perform such works. Works on a concrete road would require closure of the road for substantial periods causing traffic disruptions and impacting on resident access to properties for days or weeks rather than hours with a bitumen road.

With over 2,000km of roads in the Midcoast, the cost to concrete the roads would be over $10 billion.



Road Failures

The failure of a road can occur at any level when the load carrying capacity of the structural layer is exceeded. How that failure shows on the surface gives an indication of the cause of the failure.

Potholes

A Pothole is formed as a result of the failure of the seal which then allows the underlying stone to be plucked out by passing vehicles.

A pothole without any deformation to the surrounding pavement indicates that the bitumen has broken down and the solution is to simply refill the hole and replace the bitumen seal. Such a repair can be undertaken by the jetpatcher or one of the bitumen teams and should last for many years.

A pothole with deformation of the surrounding pavement indicates a breakdown of the structural layers of the pavement. This can either be caused by overloading of the pavement or water ingress into the pavement that has caused the quality of the gravel or subgrade to deteriorate.

typical-pothole-no-deformation-surrounding.jpg   pothole-with-deformation.jpg

 The  photo on the left shows a typical pothole with no surrounding deformation.  On the right is a pothole with deformation of the surrounding pavement.

Filling a pothole with deformed surrounding pavement will not fix the problem. It may assist in making the road safe for a period but the failure will rapidly return. The only way to repair such a failure is to remove the damaged or wet gravel and replace it with new material. This is referred to as a heavy patch.

Heaving or rutting 

Heaving or rutting is the deformation of the pavement within the lower levels which has not necessarily caused the wearing course to break and stone to be lost. It appears as a deformation in the pavement which is often accompanied by movement of the pavement sideways.

heaving-or-rutting.jpg

 This photo shows an example of heaving or rutting.

This form of failure is caused by the inability of the pavement to carry the load exerted by vehicles. This weakness could be caused by water intrusion into the gravel from below the surface, poor quality gravels, inadequate pavement depth, inadequate compaction or deterioration of the subgrade. The solution to this type of failure is dependent on the extent of failure and may be heavy patching, stabilisation / modification of the gravel qualities or complete reconstruction.

Why does Council leave a job and come back to finish it later?

Sometimes drivers observe that the work we finished 'failed straight away' and work crews had to return to 'fix' it.  This is incorrect - what actually happens is that jobs are usually completed in stages, to be cost-effective and save money. We do a temporary seal to make the road waterproof and allow the road pavement to operate under traffic without damaging the gravel finish. We also allow traffic on the road for a while in order to highlight any weak spots before we hotmix. This is a normal process in road building. Establishment of a hotmix crew costs about $2,000 without laying any material, so it is better to have several jobs ready for completion with hotmix and we schedule the hotmix works for maximum cost effectiveness.



How does Council prioritise roadworks?

Road construction and maintenance is extremely expensive. We can’t simply seal every road in the region.

Apart from the cost to seal the extra 1,000km of gravel roads, as a general rule, roads which carry less than 250 vehicles per day are cheaper to maintain as gravel roads.

We currently have a backlog in roads of $180 million. This is the amount of money required to bring our roads up to a satisfactory condition. We also have a shortfall in funding each year of $5m just for roads and bridges. This is the amount of additional money we require each year to stop our road conditions deteriorating and our backlog increasing.

In order to gain the maximum benefit for our rates we undertake careful planning to assess and prioritise every road across the MidCoast region, based on factors including volume of traffic, road conditions, maintenance costs and safety.  From there, we produce road construction and maintenance programs, which allocate the available budget to maintain roads to the best standard we can, while undertaking construction works where they are most needed.  We also have long term plans to gradually improve our roads, based on seeking future additional funding from Federal and State Government grants and rates increases.

In accordance with current engineering best practice, we prepare Asset Management Strategies and Asset Management Plans that assist in making decisions on how the annual budget is allocated and what revenue is needed in future years to ensure that assets remain serviceable for the community. Our planned Capital Works Programs (Roads, Bridges, Footpaths and Drainage) are funded by Council (unless we have noted otherwise) and include:

Urban Road Rehabilitation

Urban Road Construction

Urban Road Reseals

Rural Road Reseals

Rural Road Rehabilitation

Rural Road Construction

Regional Road Gravel Re-sheeting

Rural Bridge Construction - loan funded

Regional road rehabilitation / construction - jointly funded by Council and funded from Roads and Maritime Services (RMS)

Regional Roads Reseals - funded from Roads and Maritime Services (RMS)

Footpath / cycleway construction

Traffic facilities management

Stormwater drainage construction - partially funded from the stormwater management charge on your rates notice.

As the merger progresses, we will be providing our forward plans so that you can see the individual roads and streets that will receive road works for the upcoming year. Watch this space!


Maintenance


Linemarking

You know that lines on the road make driving easier. 

Linemarking gives us clearly defined traffic lanes, roads widths and alignment.

Reports have proven that linemarking can reduce car accidents by up to 60%, and with correct levels of contrast and brightness, the reflective lines can prevent crashes at night on bends on rural roads.

Linemarking is an essential element of a modern road system and also the most cost effective road safety measure. 

Mr Paul Gibson, Chairman of the NSW State Government’s StaySafe committee believes the simple white reflective lines dividing a road are just as important as speed cameras and random breath tests and are the most fundamental counter-measure ever introduced into road safety.  



Roadside vegetation management

We manage roadside vegetation across the region on sealed and unsealed roads to improve visibility and safety for drivers, cyclists and pedestrians.

Roadside vegetation management is however a very expensive use of Council resources.

Residents can help free-up Council funds for other road maintenance by looking after their own road frontage.



Drainage Management

Good drainage is essential to a safe and efficient road network.

Why is drainage so important?

Efficient removal and disposal of water contributes to:

  • improved road safety by preventing a loss of friction between tyres and the road
  • increased visibility (because spray is reduced)
  • prevention of flooding of the road and adjacent areas
  • protection of our roads by preventing water from weakening the road pavement
  • reduced erosion of embankments
  • reduced environmental impacts in not just the vicinity of the road but also beyond


Pothole Response - Patching

Potholes form when a crack in the bitumen surface of a road allows moisture to enter the pavement. The pavement may soften slightly or water may penetrate horizontally under the bitumen surface.  In either case, a small area of the cracked surface is likely to lift out under the action of traffic, starting a pothole.  Potholes usually appear after rain. 

This is an effective and cost-efficient way to improve roads and makes them safer. Pothole repairs can prevent further deterioration of roads, saving us from more expensive and extensive repairs.  We generally undertake repairs using the jetpatcher, paveline bitumen repair or coldmix.

The jetpatcher is a purpose built machine that pumps bitumen and gravel into holes under pressure. As a result of this pressure application, the repair material does not require compaction. In order to prevent issues with free bitumen a layer of dry gravel is applied to complete the hole and this remains in a loose state until it is dispersed by passing vehicles. This loose gravel is often the source of complaints by motorists.

jetpatcher.jpg

The jetpatcher (pictured above) is the most cost effective form of filling potholes due to its fast application rate and is the most effective in term of OH&S as there is limited manual handling involved. All operations are performed from within the cabin of the machine.

The paveline truck (see photo below) is the conventional form of repair consisting of a bitumen spray wand and manual gravel application. This form of machine is preferred in the southern area as it is more flexible and able to perform functions other than basic pothole repairs. 

paveline-truck.jpg

Coldmix is a premixed bitumen and gravel matrix that is manually placed in holes. Compaction is by way of treading on the mix and further compaction is undertaken as vehicles travel over the filled holes. Although it is a fast application it is more porous than alternate repair materials and therefore has limited life. It is generally used during times of particularly bad weather to supplement other repair methods as it does not require purpose built machines. Coldmix can be applied manually by shovelling from a ute. 

Hotmix for pothole repair does not work in a large rural area such as MidCoast Council because the travel times between the hotmix plant and the job are such that we would need a heated truck to maintain the material in a usable form. In addition, hotmix does not successfully repair potholes on roads with a chip seal due to the different properties of the two materials and the need for proper compaction while the material is still hot.

Read more about potholes under "Road Failures".



Gravel Patching

Pavement materials that make up the surface of an unsealed road are lost over time as a result of degradation, wind and rain, scour and traffic abrasion.

Gravel patching is the process of replacing these materials to create a safer driving surface.  The purpose of grading is to keep the road well drained and to maintain a satisfactory wearing surface for road users.



Shoulder Grading

The road shoulder is the portion of the road adjoining and flush with the pavement and extends out to the traffic inside guide posts or safety barriers.

Shoulders can be sealed or gravel.

A shoulder should have a smooth running surface, a minimum of loose material, an adequate slope for drainage, sufficient strength to support wheel loads and a surface flush with the pavement edge.

Shoulders are important to:  

  • provide lateral support to the pavement
  • carry surface water clear of the pavement to table or batter drains
  • prevent or minimise moisture getting into the pavement
  • provide extra width for traffic to stop or stand, or for use in emergencies  
  • provide overtaking and passing movements, particularly on single lane roads
  • create a sense of open space and thus increase the effective use of traffic lanes.

Shoulder grading and maintenance improves traffic safety by providing a clear and uniform zone to the immediate edge of the traffic lane.  It also extends the life of the road by allowing water to drain quickly away and not remain pooled on the road. 



Safety Barriers

Safety barriers, guardrail or guard fencing helps define the roadway, deflecting traffic from hazardous locations, and reducing the severity of accidents where vehicles may otherwise leave the road. Guardrail is commonly used, although the older types of post and cable, post and chain wire, and wooden post and rail can still be found throughout rural areas.

In a safe system, roads (and vehicles) should be designed to reduce the incidence and severity of crashes when they inevitably occur and safety barriers are an important part of reducing these risks.


Renewal


Heavy Patching

Heavy patching refers to road repairs involving the excavation of existing road material. It is undertaken to repair a single pavement failure or before a road reseal to repair any failures prior to the new seal is applied.

The road is reconstructed in layers as described above (see "Road Structure") once the failed material is removed. The depth of reconstruction is dependent on the layer at which the failure has occurred, ie if the failed layer is the sub-base, this layer will be removed and replaced. If the fault lies below the road pavement it may be necessary to remove the natural material and replace it with better quality material.

Sometimes, particularly on arterial roads managed by Roads and Maritime Services (RMS), gravel material is replaced by deep lift asphalt. This is the term used to describe asphalt placed in thick layers, ie 100mm to 200mm. This is very expensive but is done when there are doubts about water penetration, need for speedy repairs or the need to increase the load bearing capacity without removal of deep gravel layers or increasing pavement depths.



Surface Resealing

Resealing restores a worn road surface and protects the underlying road structure.

The resealing process itself does not overcome structural imperfections in the road itself, so the road will not exactly return to 'as new' condition.

Resealing can only be undertaken if the underlying pavement is in a sound condition.  If not, repairs are conducted prior to the reseal, including repair to potholes and edge breaks, and for more extensive deterioration, heavy patching.

Increasing the frequency with which we reseal roads leads to greater protection of the underlying pavement, and in turn prevents deterioration.

Resealing a road is a bit like adding a layer of paint protection or polish to your car - it stops the surface of the road degrading as quickly.

Like with your car's paint protection - it is only effective to apply resealing to a surface in sound condition.

That's why it sometimes might look like we are working on a road that is already in reasonable condition. It's important to understand that this is not a "waste" of our resources. Long term it makes more sense and is most cost-effective, as it maximises the lifespan of a road.

The process involves applying bitumen and aggregate to the surface of a road, providing a smoother surface and waterproofing the underlying gravel pavement.

It also ensures a dust free, skid resistant surface which enhances comfort for road-users and improves safety conditions.



Gravel Grading & Resheeting

There's numerous unsealed roads in our region and many of us frequently travel on gravel roads.

Grading

Dedicated patrol grading teams, each comprised of a grader, water cart and roller undertake grading on gravel roads across the MidCoast. The grading undertaken by these teams is complemented by a gravel re-sheeting program.  An annual road grading program, based on available budget, volume of traffic and road conditions is determined. Roads that experience higher traffic volumes are generally the ones that connect our road network. Because of the faster deterioration of these roads through higher use, and the additional risks these roads pose to the public, they receive more regular maintenance. Weather conditions will also impact on the way we plan patrol grading - extended wet or dry periods may delay grading work. A patrol grading team is able to grade about 6km of road every day. This means that on average, each patrol grading crew can grade up to 30 km of road per week, depending on favourable weather conditions. As a result some roads (that have higher traffic volumes) are maintained up to twice a year.

Resheeting

Gravel resheeting is the process we use to maintain the life of a gravel road surface.  It involves the application of a 100 – 200mm layer of new gravel over the existing gravel road surface.

Resheeting is the process of adding suitable material over the full width and length of a specified section of unsealed road. This is undertaken to restore the thickness of the pavement in order to provide adequate support for vehicles using the road. Gravel re-sheeting costs $50,000 per km on average. The process is intricate, depending on the condition of the road and other topographical constraints. Council periodically applies new gravel to roads in isolated areas that are deteriorating significantly. This is undertaken by Council’s patrol grading teams when they are in the area.

Gravel resheeting targets repairs to pavement failures by either excavating existing defects and replacing with suitable materials or modifying existing failed areas by stabilising with an additive.  



Rehabilitation & Reconstruction

Rehabilitation and reconstruction works are the major, high-expense projects that must be undertaken when a road is beyond repair.  

We focus on treating roads before they reach this point, we aim to minimise the amount of reconstruction work required into the future.

These works are often combined with an element of upgrade, most frequently lane widening, to maximise  long-term value and cater for future needs of those using the road.

On a regional road, reconstruction works are sometimes good candidates for State and Federal Government grant funding, because they are specific projects. We do not receive grant funding for 'local' roads.



Stabilisation

Stabilisation refers to the modification of the gravel qualities through the addition of another material. Materials generally used in the MidCoast region include cement, slag, and lime

Cement is used when the gravel is highly granular whereas lime is used when there is a higher clay content which is generally referred to as a plastic material. Lime binds the very fine clay particles together and brings the performance closer to that of a granular material.

The advantages of stabilisation are that it increases the strength and quality of the gravel and makes the gravel less susceptible to water damage. It is also highly cost effective when compared to reconstruction.

The amount of material introduced in a stabilisation process varies between 1% and 6% of the mass of the gravel, although it is generally about 2 or 3%.

If the amount of binder is increased above approximately 4% the gravel is referred to as heavily bound and performs more like concrete than a flexible pavement. Whilst this may be thought of as a good result as concrete is stronger than gravel, it is actually detrimental to the life of the pavement. The reason for this is that the gravel binds heavily together but the layer of gravel cannot act like a concrete slab and resist shrinkage and swelling forces. The result is that it will crack at regular intervals with cracks larger than the hairline cracks found in a lightly bound pavement. These cracks will then reflect through the bitumen and allow the ingress of water into the pavement eventually leading to premature failure. This form of failure is referred to as block cracking because it resembles cracks in a uniform block pattern.

If cracks occur in the seal, they need to be waterproofed and this is done by filling the cracks with bitumen and is referred to as crack sealing.