A76 Ex-Situ Recycling

A76 Muirside Culvert - Croftmaggot Road

Amey proactively engages with our supply chains when carrying out road maintenance to minimise embodied carbon in materials and reduce waste products. In July 2021, the South-West Trunk Roads team trialled ex-situ recycling on the A76 at a resurfacing scheme between Muirside Culvert and Croftmaggot Road. High levels of coal tar were identified within the base and binder layers of the road pavement during the investigation phase of the scheme. As a result, the decision was made to recycle the tar bound material from the work extents as well as tar bound materials from other nearby sites through ex-situ recycling.

Ex-situ recycling involves the reuse of planings to construct a new road surface. The planings are moved to a nearby quarry, reprocessed, and encapsulated before being brought back to site and re-laid as the base layer of the road pavement. For the A76 scheme, a mobile unit was installed at the quarry where the tar bound planings were crushed and regraded with the addition of 7% PFA (Pulverised Fuel Ash, a by-product of the coal industry), which was then loaded into the Recofoam plant with cement (1%) and bitumen (3%).

In total, 3600 tonnes of planings were recycled via this process and the carbon saving from the project was 200 tCO2 (e). This amount of carbon is the equivalent of driving 500,000 miles in a regular diesel car. The environmental benefits of the project included eliminating landfill disposal of tar bound materials, minimising lorry journeys to transport the planings to a hazardous waste landfill (the nearest of which is in Northern England), and reducing the quantity of virgin aggregates needed for construction. The reprocessing of planings via ex-situ recycling is also less energy intensive than the manufacture of virgin aggregate materials. A76 Muirside Culvert to Croftmaggot Road is the single largest ex-situ recycling project undertaken to date within Scotland and Amey intend to implement the process in future schemes across the South-West road network.

Process Diagram of Ex-Situ Recycling