A Green Take on Road Renewal

As pressure to reduce CO2 emissions grows worldwide, environmental advocates and governments are focusing efforts on one of the biggest culprits: transport.

It is no secret that the burning need for fossil fuels is raising the amount of CO2 emitted into the atmosphere by transport, encouraging efforts from around the world to come up with greener alternatives such as hybrid vehicles and more economic aircraft.

Transport infrastructure, however, has largely been overlooked, but a new generation of equipment designed precisely to recycle existing materials and reduce the enormous amount of resources needed to maintain transport networks has begun to make a difference.

A global patchwork

The main advantage of road recycling is that repairs are conducted using the exact same broken material the original road is made of, a process that saves energy, raw materials and time, and ultimately produces a reliable surface with far less damage to the environment.

To encourage the uptake of road recycling in Europe, the EU has launched the DIRECT-MAT (dismantling and recycling techniques for road materials) initiative to share knowledge and practices on road recycling with the aim of ensuring sustainable prospects for road infrastructure.

DIRECT-MAT forms part of the EU’s seventh framework programme of research (FP7), which runs from 2007 to 2013 and is intended to identify practice-orientated data from research projects across Europe to provide a web database for the European community.

Outside of Europe, road recycling is also attracting a lot of attention. According to the US Road Recycling Council website, the method has been adopted across more than half the US states and has been used to good effect on projects including Fort Worth’s large-scale street maintenance programme, and across many areas damaged by flooding and hurricanes.

Reworking with infrared

One of the driving technologies in road recycling is infrared repair, a process where existing damaged tarmac is super heated, reworked and rejuvenated to provide a better-than-new driving surface.

Pioneered by UK-based Nu-phalt infrared is used to repair surface defects by heating the macadam using a portable heater, which heats the surface defect to around 200°C creating a strong thermo-bond that reduces potential future weak points.

Other than the existing materials very little else is added. A water-based anioninc binder is added to help rejuvenate the area and in some cases a small amount of material is added to compliment the existing material.

All in all, a typical repair can take as little as 20 minutes, minimising machine time and reducing the congestion caused by roadworks – two other major factors in producing CO2. Not having any waste to dispose of is also a major plus.

Infra-environmental study

According to a study carried out by the Scottish Institute for Sustainable Technology at Heriot Watt University in Edinburgh traditional methods of road repair produce 51.62kg of CO2/m² repaired – a volume that would take at least 11 trees to reabsorb.

In comparison, the university research found that infrared repair produces 4.28kg of CO2/m² repaired, a volume only requiring one tree to reabsorb.

The university research, which was based on a 2007/8 study by East Lothian Council covering 5,245 road repair heat cycles, found that 57,999 mature trees would be needed to offset traditional repair methods, while only 4,725 trees would offset Nu-phalt’s repair method.

The results show a saving of 248t of CO2 in the East Lothian Council alone, a significant amount for a relatively small area.

To put this into further perspective, a standard small car generates around 156g of CO2/km. A savings of 248t would therefore translate as 989,009 miles saved or the equivalent of 82 cars taken off the road.

Taking it to the pavements

Road recycling as a cost-effective and environmentally sustainable method of repair has, in some areas of the UK, been used to achieve government “sustainability targets”, including the UN Agenda 21, global warming reduction initiative.

A specialist in the industry, Stabilised Pavements Ltd (SPL) prides itself on meeting Agenda 21 targets and claims to reduce CO2 emissions by around 60% compared with traditional methods.

As the name suggests, rejuvenating pavements is a speciality using the company’s Stabiltread technology whereby bituminous emulsions are reduced to rejuvenate pavements between 75mm and 100mm thick.

For badly damaged pavements, the Stabilcourse method is used by pulverising pavement material, and mixing with foam bitumen or cement binder before compacting and trimming.

Full-width road recycling is also done using the Stabilhaunch method to stabilise the carriageway using an OPC additive blended with the existing pulverised materials to improve strength, durability and permeability.

Using the Stabilsoil method, the company can also turn unsuitable and damaged materials into useful materials by blending them with lime or cement.

Brind case study

On the B1228 stretch of road in East Yorkshire in the UK, the recycling of just 2.8km of road surface was shown to save 51t of CO2.

During the project, conducted by SPL, the existing carriageway was pulverised to a depth of 250mm and reshaped to the desired level. A blended OPC / PFA was then applied with the addition of water to achieve optimum moisture content.

A motor grader was then used to reprofile the carriageway, which was then sealed using a coating and sealing grit.

A CO2 calculation conducted by SPL, revealed savings of 51t, the equivalent of 136 100W lightbulbs burning constantly for a year. The decision to recycle the road rather than patch it up also saved the local council around £170,000.

The road ahead

The plethora of advantages road recycling offers over exiting road repair methods such as patching, haunching and reconstruction is beginning to make a big impression on the road industry as well as on governments.

Increased material and energy efficiency along with lower transport fees, reduced construction time and no real need to dispose of waste all add up to provide a significant reduction in CO2, which in today’s climate of energy targets and carbon credits is no small advantage.

The environmental benefits and the proven advantages of reduced project time and financial cost make the road ahead for widespread recycling look very smooth indeed.