Thin surface course systems were first introduced to the United Kingdom from France in the early 1990s. The benefits offered by many of these materials in terms of noise reduction, ease and speed of construction, resistance to deformation and improved ride quality has seen their popularity and use increase to the extent that they are now the principal option for surfacing on trunk roads in England recommended in the Design Manual for Roads and Bridges (DMRB).
It was initially assumed that the service lives of these materials would be in the region of 8-10 years, and so this research was commissioned at time when the original installations would be reaching this age in order to obtain data on actual in-service performance, an approprriate time to assess the actual in-service performance.
This information would be extremely valuable to the Highways Agency for the purposes of network modelling, maintenance management and planning and to permit an assessment of the cost of these materials on a whole life basis.
The objectives of this research were :
- To quantify the effective service life that can be expected of thin asphalt surfacing systems, in terms of the different material groups if appropriate. In particular, to identify any parameters that significantly influence the effective service life such as, possibly, layer thickness, air voids content and/or binder film thickness.
- To identify the most likely manner(s) of failure of thin asphalt surfacings, with particular emphasis on whether it is gradual or sudden, and if the latter, what warning is given.
- To provide advice for publication in the Design Manual for Roads and Bridges (DMRB) Volume 7 on the service life of thin surfacings in terms of design considerations and maintenance procedures to extend it, advance warnings of failure and the expected value for use in whole-life costing.
- To provide advice to the Specialist Group SG3 of BBA-HAPAS to develop the 'Guidelines for the Assessment of Thin Surfacings' in terms of their durability.
This was achieved through extensive monitoring of a range of sites ditributed across the country selected to provide a representative sample of the materials in use.