Barrett Byrd Associates

Resurfacing work on one of the last local authority owned stretches of motorway in the UK is currently being fast tracked using high performance ex situ recycled materials. Claire Symes reports.

Recycling was once a technique reserved for cautious use on minor routes but resurfacing currently under way on the M62 near Liverpool shows that acceptance of secondary surfacings is growing. Highway maintenance specialists Dowhigh and Roadstone Recycling are currently laying an ex situ recycled base course on the motorway and are expected to finish the reconstruction six weeks earlier than predicted.

Main contractor Dowhigh won the contract to resurface and refurbish 5km of the M62 from Knowsley Borough Council (KBC) earlier this year and quickly convinced KBC of recycling’s benefits. Dowhigh called on Roadstone Recycling to form a partnering agreement to carry out the work using recycled asphalt planings (RAP) bound using bitumen supplied by Nynas Bitumen.

Dowhigh’s £3.4M contract involves reprofiling of the M62 between junctions 5 and 6 to improve the drainage characteristics using a regulating base course. The contract scope also includes laying of a new wearing course and refurbishment of 10 gantries and seven over bridges. The 5km stretch of motorway being refurbished is one of the last sections of the UK motorway network to fall outside the control of the Highways Agency.

“KBC are keen to promote recycling and Roadstone Recycling’s compelling technical data helped the authority take the decision to recycle,” says Dowhigh project manager Tony O’Neill. “Roadstone Recycling had also recently gained a special dispensation from the Highways Agency for a similar resurfacing project on the M6 which added weight to the proposal.”

Dowhigh’s work on site began in mid March and was programmed to take 20 weeks to complete but according to O’Neill the project is on schedule to be completed six weeks early at the end of June. Roadstone Recycling’s work was split into a number of phases, each lasting around two or three days, spread throughout the four month contract.

“Our recycling plant is a mobile unit which can be transported to wherever it is needed and set up very quickly,” says Roadstone Recycling managing director Gary Cook. “We stationed the plant for the M62 project at an industrial estate close by the site which has enabled us to rapidly process the RAP and send the recycled asphalt back to site for relaying the same day.”

Roadstone Recycling’s plant comprises of a crusher to grade the RAP and a mixing chamber where cement is added to boost the fines content before a state of the art spray bar foams bitumen onto the secondary aggregate.
“Foamed bitumen is formed by injecting air and water at high pressure into the bitumen to expand its volume,” says Nynas bitumen sales manager Steve Waller. “Expanding the bitumen in this way makes it easier to evenly spread the bitumen through the mix but it is actually the compaction during laying that coats the aggregate.”

Nynas is supplying the 150 pen bitumen directly to the mobile plant via a 30t mobile storage tank, known as a cartem, on a just in time basis at the start of each phase of recycling. “Most of our temporary recycling sites have no bitumen storage facilities, so Nynas’ ability to supply both bitumen and mobile tanks is invaluable,” says Cook.

In total, Roadstone Recycling will produce around 10,000t of recycled base course during the contract. According to Cook, only 6% of that tonnage has to be imported and even this material is a secondary aggregate. “This is probably one of the biggest motorway recycling projects so far in the UK. The environmental and economic benefits that come from recycling mean that schemes of this kind will become the norm over the next few years,” says Cook.

“Recycled material goes much further per tonne than virgin material – around 25% further – and uses 50% less bitumen too. Recycling turns roads into ‘linear quarries’ which reduces haulage of virgin aggregate plus locating the recycling plant close to the site can also cut haulage costs.”
Cook also says that the recycled base course which is currently being laid on the M62 can be recycled at least four more times before any virgin aggregate is needed.

Throughout the M62 contract, Dowhigh and Roadstone Recycling have worked closely to plan the phasing of the work. “Logistics has been a big challenge – ensuring enough material was planed out in the right places ready for recycling and relaying needed careful planning,” says O’Neill.

Final stretches of the high strength recycled regulating base course are currently being laid at the site by Dowhigh in layers between 60mm and 130mm thick. Once complete the recycled material will be topped by a 50mm HDM binder course and a 30mm layer of Lafarge’s Axoflex proprietry thin surfacing wearing course.

Proof is in the performance
Roadstone Recycling was formed in 1997 through a joint venture of Bruce Cook Road Planing (BCRP) and Tarmac to promote both the performance and environmental benefits of recycling. Since then the two companies have worked to develop the ex situ recycling technique from a low grade temporary surfacing material to the high performance material that is going down on roads such as the M62.

“Ex situ recycling is more of a precise science than in situ techniques and can, if the design is right, create base and binder courses which at least equal the performance of hot asphalt surfacings,” says Roadstone Recycling managing director Gary Cook.

BCRP, as the name suggests, started out as a specialist planing contractor but unlike other planing contractors, the company had its own haulage fleet and sold on the RAP itself. “RAP has been used in the UK for many years but only as an temporary unbound road material,” says Cook. “We could see that recycling would become more important and started to search for new end uses for RAP.”

The company looked at what other countries did with RAP and found a wide variety of techniques available in countries with less plentiful virgin aggregate than the UK. One method that caught Cook’s eye was the Canadian Foamix system and BCRP soon imported one of the Canadian recycling plants to the UK.

“We spent a long time looking at the design of the mix – the grading of the RAP, the quantity of cement and the grade of the bitumen,” says Cook. “In the early stages we used our yard near Richmond to test the mixes, then progressed to car parks.”

Roadstone Recycling was born a few months later when BCRP seconded one of Tarmac’s technical team to help evaluate the Canadian machine and its capabilities. Through these analyses both companies realised the technique had huge potential and joined forces to promote the innovative technique.

The partnership worked well – BCRP supplies the planing and recycling know how and Tarmac carries out the laying and adds kudos to the operation. Since then Roadstone Recycling has drawn on the skills of both parent companies and continually worked on research and development of Foamix to create a performance specification.

According to Cook, the next area that the partnership is looking to enhance is the bitumen used in the mix. “Until now we have only used straight run bitumen,” he says. “But we are planning to work with Nynas over the coming months to investigate the potential for using more advanced bitumen formulations.”

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