Delivering Innovation

The material was laid on a section of the M25 between junctions 25 and 26 during an overnight closure in September 2019.

FM Conway is well known for its expertise in recycled material and has previously supplied surfacing material with 50% recycled aggregate pavement (RAP) to two roads on Transport for London’s network in the A1 and the A40.

Now the company has applied this particular innovation to the SRN for the first time, designing a surface course containing 50% high Polished Stone Value (PSV) recycled aggregate in collaboration with Highways England, Connect Plus Services, Connect Plus, Toppesfield and Skanska UK.

Highways standards usually dictate that UK motorway surface courses are to contain a maximum of only 10% recycled materials, however FM Conway in collaboration with Toppesfield designed the mix specially for this project and Skanska applied to Highways England for permission to move away from their standards.

Due to the location of the project being on a motorway, PSV is an important measure of the skid resistance of the surface, and motorway surfaces require stone with a high PSV.

To create the surface course, RAP was mixed with virgin aggregate and FM Conway’s own designed and manufactured Polymer Modified Bitumen (PMB). The PMB was added to significantly improve the durability of the surface course by improving the resistance to rutting and cracking.

The RAP came from two donor sites within the Connect Plus area, where Skanska planed off the existing surface course for remedial work.

To ensure the material would be suitable, FM Conway took 24 core samples on the two sites prior to planing, before testing it in its laboratory.

Mark Flint, Head of Technical at FM Conway, said:

“Extensive core sampling and testing was imperative as we were looking for the correct grade of aggregate as well as the right Polished Stone Value (PSV). Being able to carry out the research and development at our Technology Centre and engineer a bespoke PMB at our PMB plant was beneficial to the success of the mix. 

The laboratory tests were essential to prove that the 50% RAP surfacing material would meet all the requirements that a traditional surfacing material would achieve, while being far more sustainable."

Challenges and Solutions

Utilising this innovative approach required a large amount of resources, not just in terms of materials, but also in terms of logistics and personnel.

The planings from the two donor sites were taken to FM Conway’s Colthrop recycling plant near Thatcham in Berkshire, where they were crushed, screened, tested, segregated and stored.

The day before the material was due to be laid, the planings were transported to the company’s Heathrow recycling and asphalt plant for mixing with the virgin aggregate and PMB.

On the night of the closure, FM Conway’s trucks took the mixed surfacing material to the site. A total of 260t of the material was laid by Toppesfield on a section of lane on the anticlockwise carriageway of the motorway, to a depth of 45mm.

To achieve all of this, FM Conway had to rely on a high level of cooperation between its various divisions and plants, as well as any partners on the project to ensure a successful delivery.

Skanska has a contract to carry out civil engineering and technology works for Connect Plus Services, which operates and maintains the M25 and its adjoining trunk and slip roads for Highways England, so it was crucial for FM Conway and Skanska to collaborate on this project.

Traffic Management also had to be considered when performing an overnight closure of a vital motorway on the SRN.

By keeping the works to a single overnight closure, the team could minimise disruption and the health and safety risks facing the project.

Outcomes

This project is a great example of FM Conway’s use of innovation and drive towards a sustainable future. It is also a good demonstration of the business’ ability to work well with several different partners on a given scheme.

Mark added: “The project’s success was a result of a big collaborative effort by Skanska UK, Connect Plus, Toppesfield and FM Conway.”

The project has proved to be ground-breaking in showing that higher percentages of RAP content should be used on the SRN in our bid to achieve more environmental benefits within our work in the industry.

Aggregate and bitumen are finite resources, whereas planings are readily available as a by-product of road improvements and we should consider using them to reduce both carbon emissions and transport movements.

Mark explained: “Quarries and bitumen won’t last forever, but there is a quarry out there – in the form of existing roads – that we can tap into and use. Recycling worn out material from the road network enables us to stop importing so much material and bring it form only a few miles away.”