Performance review of surfacing materials with enhanced levels of reclaimed asphalt

Current UK specifications permit up to 10% of reclaimed asphalt (RA) to be routinely incorporated into surface courses. The incorporation of RA provides significant economic and environmental benefits by effectively using recycled materials. Trials of thin surface course systems incorporating more than 10% RA have been installed on the strategic road network since 2004, and have demonstrated the feasibility of incorporating higher RA contents and the necessary quality controls. The trial sites have now been in service for a significant period, providing an opportunity to understand their performance. Current practice and trials undertaken for >10% RA contents in the UK are summarised in this paper. Detailed analysis of the performance of junctions 6–7 and 7–8 of the M25 clockwise (23% RA, installed in 2007) and junctions 7–6 of the M25 anti-clockwise (40% RA, installed in 2009) is presented. Quantifiable evidence regarding the performance of surface course materials containing RA > 10% is provided. The analysis demonstrates that surface courses containing RA have performed equivalently to control sections containing no RA over a significant period of time. The trials indicate that the inclusion of RA, when subject to the appropriate quality control processes, has had no detrimental impact on skid resistance. The conclusions support the incremental increase of the maximum permitted RA content from 10% to 20% with appropriate quality controls in the future revision of PD 6691:2015.