Knowledge base On the surface Dr Michael Wright, Practice Manager, Engineering, Design and Project Management Transportation at Connect Plus Services, explains more about a trial to reduce the carbon footprint of one of Europes busiest motorways with the first use of 50 per cent reclaimed asphalt in its surfacing works The M25 is one of the most strategically important transport assets in Europe. More than 200,000 journeys take place on the 440km UK motorway every day. The M25 Design Build Finance Operate (DBFO) project, managed by Connect Plus and Connect Plus Services (CPS), is committed to delivering National Highways sustainable development action plan and net-zero highways 2050 plan. Resurfacing represents one of the largest carbon footprint contributors associated with maintaining the M25 pavement asset. In addition, the supply and cost of finite primary resources, such as high-quality aggregate and bitumen, present a significant long-term business risk. Connect Plus and CPS recognised the need to minimise the carbon footprint associated with resurfacing to deliver the strategic sustainability action plan. So, the M25 community set about leading the way through surface course recycling to minimise the carbon impacts of maintaining the pavement asset. By maximising the reuse of resources already available on the network, demand for primary resources is reducing, which has significant economic and environmental benefits. Asset management first The M25 has a proven history and culture of promoting sustainable surfacing solutions using reclaimed asphalt (RA) generated from road surfaces that have reached the end of their life. Since 2007, several trials have been undertaken using increasing levels of RA. While reuse of RA in asphalt mixes is not new, current specifications limit the percentage of RA in surface courses to 10 per cent. This means that significant volumes of high polished stone value (PSV) aggregate and bitumen are imported every year to deliver National Highways resurfacing needs. Connect Plus and CPS were keen to build on historic success and continue to minimise the environmental impacts of operating, maintaining and improving the strategic road network (SRN). Together with National Highways, they established an expert team to deliver a surface course mixture incorporating 50 per cent RA, which represents a first for the maintenance of assets on the SRN. By maximising the reuse of resources already available on the network, demand for primary resources is reducing, which has significant economic and environmental benefits Leading the way on the M25 2007 M25 J6-7 trials of MasterPave with 23% reclaimed asphalt Existing standards 10% reclaimed asphalt 2009 M25 J6-7 trials of MasterPave with 40% reclaimed asphalt 2019 Trial of surface course containing 50% reclaimed asphalt installed on M25 2016 M23 J8-10 Ultipave with 30% reclaimed asphalt Figure 1: History of surface course recycling on the M25 A first on the strategic road network No reclaimed asphalt incorporated into thin surface course systems Implementation and innovations To deliver this step change in lower carbon pavement asset maintenance, an expert delivery team was assembled, comprising Atkins, Skanska UK, FM Conway and Toppesfield. The team undertook detailed investigations to identify suitable donor trial sites on the M25 in accordance with best practice. This was followed by detailed processing, characterisation of the recycled material and an extensive design process. The performance testing that was undertaken exceeded the testing required in national standards. The innovative approach demonstrated the performance characteristics and long-term durability of the surface course, and gave National Highways confidence to approve a departure from standard. The innovative surface course was successfully produced at FM Conways state-of-the-art asphalt plant at Heathrow. It is one of the leading plants in the UK in terms of recycling capability. The recycling process was conducted to the highest quality standards. All aspects of the donor site selection, RA processing, production and installation were conducted in accordance with ISO 9001:2015 quality management system and a recycling specific quality plan. The trial was successfully installed on the M25 between junctions 25 and 26 in September 2019. There has been extensive monitoring since to inform the asset management strategy. Sector first The innovative trial represents the first surface course to be installed on the strategic road network (SRN) containing 50 per cent RA, marking a step change in the use of recycled material on the National Highways network. BS EN IS9001:2015 quality management system Recycling-specific quality plan Post-installation verification Installation method statement and latest development in paving technology Detailed investigation and selection of donor site Ensure durability and skid resistance to deliver long-term sustainability and safety benefits Production using latest RAP drier technologies Figure 2: Implementation process Detailed laboratory characterisation of reclaimed asphalt State-of-the-art mix design Key results The innovation has resulted in significant economic and environmental benefits associated with maintaining pavement assets on the M25, including: 1) Reduced use of primary resources: 50 per cent reduction in high PSV aggregate demand (limited resource) 61 per cent reduction in polymer modified bitumen (through use of bitumen from the RA) 58 per cent reduction in embodied carbon. 2) Protecting and enhancing the quality of the surrounding environment by: Reducing the demand at quarries and refineries for primary materials. 3) Significantly reducing transportation through the use of existing RA on the M25: Eliminating 730km of shipping associated with aggregate importation Eliminating 38km of road haulage Reducing shipping associated with bitumen importation 43 per cent carbon footprint reduction associated with transportation. Carbon footprint calculations using the industry-endorsed asPECT calculator demonstrate a 9.46kg CO2e/T saving compared with traditional mixes. Carbon footprint (kg CO2e/T) 100.00 90.00 Transport of materials 80.00 70.00 Figure 3: Carbon footprint benefits (graph excludes future recyclability) Constituent materials 60.00 50.00 Production heating and drying 40.00 30.00 20.00 Asphalt plant electric (excluding heating and drying) 10.00 0.00 Standard thin surface course Resurfacing represents one of the largest carbon footprint contributors associated with maintaining the M25 pavement asset M25 thin surface course incorporating 50% RA Ongoing monitoring The trial is being monitored continuously and subjected to significant traffic loading during its lifetime (>7,500 commercial vehicles per day). The performance testing undertaken demonstrates excellent performance. Skid resistance testing of the asset has demonstrated very high levels of resistance with a Sideway-force Coefficient Routine Investigation Machine (SCRIM) coefficient of 0.57 achieved. This is equivalent to the control material and significantly above the investigatory level of 0.35 required for the assets, demonstrating a high level of safety for road users. The M25 strategy represents a step change in use of recycled material on the SRN and low-carbon maintenance of pavement assets. This will inform future standards and provide long-term benefits to the environment that create a sustainable future. The project won the Asset Management Excellence Award for Sustainability and Climate Impact 2021. To find out more, see page 15