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Command performance

Highways - The UK asphalt sector has been developing a new breed of high performance asphalt for UK roads.

First full scale commercial use plus a comprehensive new specification is marking the arrival in the UK of the latest generation of high performance asphalts - EME2. This is effectively the end of a three year collaborative research and development programme initiated in response to problems encountered with High Modular Base (HMB) course materials.

The problems prompted a Highways Agency moratorium on the use of HMB15 and HMB25.

But work by the asphalt sector, followed by successful trials, means that high strength, long life asphalt base and binder courses are available again to road owners and maintainers.

The rst major British use of EME2 - the French Enrobé à Module Elevé - has been on a road surfacing contract on the M876 near Stirling in Scotland.

This was carried out by Tarmac with Nynas Bitumen.

EME2 development has been overseen by the Highways Agency, Quarry Products Association (QPA) and the Refi ned Bitumen Association (RBA). The project began in 2002 and the results have been published in TRL Report 636.

Initially, the three R&D principals looked to France, where high strength, long life asphalt pavements have been laid successfully for some years.

EME was originally developed there and EME2 is the long life asphalt system now used on French roads. Much work was required to make the technology applicable in the UK.

Essentially, an EME2 asphalt has a high content of hard bitumen binder combined with a carefully graded and smaller sized aggregate. The hard binder of typically 15/25 Pen grade bitumen mixed with a close aggregate grading gives high stiffness and deformation resistance and the high content of binder produces very good resistance to fatigue and cracking. There are also benefits of workability and laying quality due to the high binder content.

Most important and crucial to the development of EME2 mixes, however, is the fact that each combination of aggregate and binder has to be designed to meet exacting performance criteria. So there cannot be a single recipe for all types of stone, but instead a specific mix design worked out for each aggregate source.

Development of EME2 design, mix and laying procedure continued to roll forward with a small trial in the pavement test facility at TRL. By 2004, further laying trials were under way.

'The asphalt producers, bitumen producers and Highways Agency all worked together to produce the first draft of an EME2 specification for use on UK roads, ' says Tarmac director of technology and quality standards Colin Loveday. 'The draft specification was agreed towards the end of 2004 and is now being used for further full EME2 pilot contracts.' The largest EME2 contract so far, and the first to use the draft specification under fully commercial conditions, was the Stirling project, undertaken in May this year. Two EME2 layers were laid, one of 110mm over another of 150mm - effectively providing high strength base and binder courses - with a 40mm layer of Tarmac's Masterflex thin surfacing over the top.

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