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. 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.