Performance review of surfacing materials incorporating enhanced levels of reclaimed asphalt

In the UK, current specifications permit up to 10% of reclaimed asphalt (RA) to be routinely incorporated into the surface courses. The incorporation of RA provides significant economic and environmental benefits by effectively using recycled materials. Trials of thin surface course systems incorporating RA contents of more than 10% have been installed on the Strategic Road Network (SRN) since 2004. These trials demonstrated the feasibility of incorporating higher RA contents and the necessary quality controls. The sites have now been in service for a significant period of time and provide an opportunity to understand their performance. This paper summarises current practice and trials undertaken incorporating RA content >10% in the UK. The paper presents detailed analysis of the performance of the M25 J6-7 & 7-8 Clockwise (installed in 2007 incorporating 23% RA) and M25 J6-7 Anti-clockwise (installed in 2009 incorporating 40% RA). The paper provides quantifiable evidence regarding the performance of surface course materials containing RA >10%. 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 upon on the 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 PD6691.