In recent years, additional generic types of asphalt surfacing materials have become available for use on road and airfield pavements. In particular, thin surfacings have taken over from other asphalt materials in the last 15 years. Not all engineers are supporters of these new options; some clients try to use the new alternatives to replace more traditional materials, and others tend generally to stick to the more traditional varieties. However, the best approach must be to take all the available types of asphalt surfacing into consideration, so that the best option can be selected for each individual case.
Each type of surfacing encounters different issues according to the prevailing conditions at each site. This is because the relative importance of their different properties will change dependant upon the site’s specifications. Therefore, universally adopting the use of any one type of surfacing, would lead to the surfacing being used in unsuitable locations.
In order to encourage engineers to think about which material type should be used, a seminar was held at SCI’s headquarters in Belgrave Square on Thursday, 15 October 2009 to review the advantages and disadvantages of the various types of hot mix asphalt that are available. Cliff Nicholls introduced the meeting and reviewed some less common types of surfacing, including porous asphalt and mastic asphalt. He was followed by three experts from the County Surveyors’ Society who discussed the three most popular types. Keith Grant of Devon County Council started with stone mastic asphalt – the upstart new-comer to the UK – and other thin surfacing systems. John Thorpe of Lancashire County Council continued with hot-rolled asphalt, the ‘traditional’ option for major roads, and David O’Farrell of Capita Symonds completed the day with coated macadam (now called asphalt concrete); the ‘traditional’ option for minor roads.
We hope that the seminar stimulated engineers to consider that the mixtures they propose to use on a site properly meet the requirements specific to that site.
- The image shows damage to a thin surfacing on a roundabout, a highly-stressed location
Dr Cliff Nicholls
SCI Construction Materials Group and TRL Limited