A new surface course specification developed by Transport Scotland and TRL for the Scottish Trunk Road Network, should help deliver significant improvements in material durability, which ultimately will result in less disruption to road users generated by road construction and maintenance.

So how has this come about?

Following on from European developments in asphalt technology in the mid 1990s, a change in the type of road surfacing, known as thin surfacing, was introduced across the UK. These proprietary surfacing systems came with a range of benefits including improved deformation resistance, speed of application, noise and spray reduction and changes to traffic management practices.

In response to this, Transport Scotland commissioned a review of the performance of thin surfacings as laid on the Scottish Trunk Road Network by TRL. The review encompassed site inspections to identify and quantify surfacing defects and a series of workshops to discuss the findings and to find possible remedies to improve the performance of the surfacing.

Out of the workshops the Transport Scotland Pavement Forum (TSPF) was established who implemented annual monitoring of the surfaces, to provide an estimate of service life based on performance. This resulted in a major recommendation being made that efforts should be made to reduce the open nature of the materials by specifying denser binder rich mixes and smaller stone sizes.

A series of road trials followed using different sized aggregates based on German specifications and experience where the use of smaller aggregate sizes and higher binder content are used to enhance material durability. Study visits were also made to Germany both before and after the trials, initially to gain knowledge and then to refine the development of a new surface course specification for Scotland.

As a result of this work, Transport Scotland has been able to give final approval to a new surface course specification (1) for the Trunk Road Network in Scotland (2). It marks a step change in approach for specifying surfacing material and should provide key benefits in terms of material durability and value for money, something to be welcomed at a time of reduced funding.

And for road users, this means they should suffer less disruption to the network caused by construction and maintenance works.