EME2 (Enrobe à Module +leve) is the generic title for high strength, long life asphalt base and binder courses whose extra cost compared to conventional asphalt is supposedly offset by the benets they provide.
These include better workability, improved impermeability and greater resistance to cracking and deformation, adding up to pavements that do not deteriorate under prolonged heavy use.
The arguments for using EME2 are persuasive but have so far failed to convince the majority of Britain's road building fraternity, who are reluctant to pay a premium for anything unless the case for doing so is irrefutably proven.
That said, a signicant minority, including Scottish engineers, is rapidly coming to the conclusion that using EME2 really is sensible, in terms of value and the environment.
Up north, EME2 has been used on two projects and, according to Transport Scotland, is likely to be the preferred alternative to conventional materials on many schemes in the future.
EME2 was developed in France, where it has been used for some time with some considerable success. It constitutes the latest generation of high performance asphalts.
It features comparatively small aggregates and a high binder content that produces a more homogeneous mix that is less likely to segregate, is more easily compacted and has a lower air voids content.
Its adoption in the UK was prompted by durability problems encountered with high modular base (HMB) course materials and by approval two years ago in a comprehensive TRL report that was partly sponsored by the Highways Agency.
That same year, a major trial of EME2 was carried out on the Bankfield to River Carron section of Scotland's M876, by Tarmac assisted by Nynas Bitumen (NCE 29 September 2005).
This trial went well and Tarmac's subsequent report stated that: 'There is the potential for making a step change improvement in the durability of asphalt pavements on major roads in Scotland.' The trial was followed in February 2006 by publication of the UK Design Manual for Roads and Bridges seventh volume, that introduced EME2 as a permissible base material for flexible and flexible composite design. It also emphasised that integrating the principles of sustainability can include using pavement designs that give good value in whole life cost terms.
The message was not lost on Scotland. Within a short time, Transport Scotland had issued a letter formally sanctioning the use of EME2 on trunk roads and Tarmac was bidding to use the material on perhaps the country's most desperately needed road scheme, the improvement of the southern approaches to the Forth Road Bridge.
Transport Scotland's letter, distributed to all organisations with an interest in roads development, had a map attached to it showing routes where traffic volumes and pavement durability issues 'would warrant the option of using EME2 for maintenance works to provide value for money where it can be demonstrated that a 'long life pavement' could be designed'.
'Our strategy is now to use EME2 on trunk roads where appropriate, ' conrms Transport Scotland's materials and quality assurance adviser Dougie Millar.
An appropriate binder layer of EME2 should also be thinner than the two layers of HDM it replaces, providing a reduction in the number of interfaces as well as materials used.
Millar thinks that EME2 with a high performing thin surfacing on top makes for an ideal trunk road pavement. One that is durable and of potentially very long life, with an easily maintainable surfacing and with minimal environmental impact.
The hard bitumen binder in EME2 is typically of 15/25 PEN grade, the aggregate of 20mm nominal single size. Mix design is a crucial matter for EME2: each blend of aggregate and binder has to be designed to meet exacting performance criteria which in practical terms means that each aggregate source requires individual attention.
In terms of design, no one size fits all.
Tarmac has conducted a considerable amount of research into the design and application of EME2, under its director of technology and quality Colin Loveday. On the M876 trial, the contractor made use of the knowledge of Nynas plus the bitumen supplier's laboratory in Belgium, to obtain confirmation of the physical and mechanical properties of the final blend.
'We provided Tarmac with comprehensive technical support during the early development stages of EME2 for Scotland and England, ' says Nynas asphalt engineering support manager Jukka Laitinen.
'Tarmac ubsequently acquired the complete range of EME2 design equipment from France and has carried out all the work itself for the Forth Road bridge approaches.' The 5km M9 Spur extension will open later this summer (NCE 18 January).
Morrison Construction is main contractor to client the City of Edinburgh Council, with Tarmac Scotland responsible for the pavement asphalt, including 25,000t of high strength, long life EME2.
EME2 is being used along heavily laden sections of the A90, for its strength and durability. The 15/25 PEN bitumen binder is being supplied by Nynas from its refinery in Dundee - 'a refinery well sited for delivery to anywhere in Scotland', according to Scottish sales manager Nigel Hardy - while the 20mm nominal aggregate is coming from Tarmac's Cruicks quarry, also north of the Forth. Thin surfacing is by Tarmac Masterflex.
Morrison Construction project manager Alan Smith has been impressed. 'EME2 is an option for our projects as a product that will provide a stiffer and more durable cost effective pavement for our client. And we as a main contractor will of course benefit from reduced maintenance risk, ' he says.
'The EME2 has gone down very well and we have high expectations of its performance, ' says Tarmac Scotland's contracting director Roy Di Duca.
'We rmly believe that, if the UK highway authorities embrace and promote EME2 as they should do, then they will resolve the issue of durability once and for all.
'True, EME2 costs a little more in the first instance, but for that you get a greatly enhanced life expectancy.
'It really is a folly that EME2 is not the material of first choice for principal routes.'