Proprietary thin asphalt surfacing systems were first introduced into the United Kingdom in 1991, since when they have taken a growing proportion of the market. The first applications of these products took place ten years ago and sites with these surfacings will increasingly need replacing, making the old material available for recycling. The need to recycle thin surfacing systems as part of efforts to promote sustainability within road construction is more critical than with many other generic surfacing materials because of the quantity of relatively scarce aggregates with high skid-resistance properties within the layer. Laboratory investigations of have been undertaken and trial sites have been successfully constructed. The trials were on the access road to Renishaw asphalt plant near Sheffield, and on the HA road network at the A1(M) Hatfield and A405 Bricket Wood, including the use of polymer modified binders (PMBs) and up to 30% recycled asphalt (RA) in the mixed asphalt. These trial sites were assessed for visual condition, density and texture depth and material sampled from them for determination of grading, recovered binder and resistance to permanent deformation. The findings demonstrate that 10% RA can be easily added to new materials without affecting grading. As the proportion of RA increases up to 30%, greater care needs to be taken on assessing grading compatibility and how to treat the residual binder present in the RA as a proportion of the ‘active’ binder content in the recycled surface course layer. To-date all of the trials are performing well, although some problems occurred during construction which were caused by factors other than the inclusion of RA. (Author/publisher)
Abstract