Spillage of volatile liquids like diesel can reduce the most durable asphalt to loose stone - hence the use of other materials for aircraft standings, lorry parks and the like. But this is set to change.
An asphalt surfacing with all the traditional advantages of asphalt plus the benefit of resistance to volatile liquids should be of considerable interest to the specifiers of pavement where spillage is likely to occur.
These were the thoughts of Tarmac Quarry Products, which prompted the joint development of a fuel resistant asphalt with bitumen specialist Nynas UK.
Nynas claims Nyguard binder means that for the first time infrastructure specifiers can include asphalt in their range of pavement options for situations where spillage is a possibility. Users will be able to move and park their planes, buses or trucks on asphalt, confident that the surfacing will remain serviceable under normal use.
In construction materials terms, industry estimates put the total area requiring fuel resistance in Britain at more than 80Mm2, with new build and maintenance at around 2Mm2 each year. Of this, most is carried out using concrete or block pavers. Neither of these pavement types fulfil all requirements, according to Nynas technical manager Dr Ian Lancaster.
'Concrete discolours and block pavers can become dislodged and uneven - neither of them provides the flexibility and quiet running of asphalt. To provide an asphalt alternative, all we had to do was develop spillage resistance,' he says.
This was easier said than done. Conventional asphalt is vulnerable to damage by liquids such as diesel, engine oil, hydraulic fluid, de-icing compounds, petrol and aviation fuel - which are spilled or drip over a period of time.
The asphalt sector has some experience of products which provide fuel resistance. In terms of solubility, tar has a very different profile to that of petroleum-derived bitumen and can serve as an effective binder largely unaffected by the spillage of deleterious liquids.
'However, tar is a relatively scarce commodity these days. In addition, there are health and safety issues associated with its use,' says Lancaster.
The way forward, Nynas and Tarmac decided, was to develop a fuel resisting binder which could be incorporated in an asphalt mix with a structure that itself resisted the ingress of diluents. Nynas went ahead and developed Nyguard, a high quality modified bitumen unaffected by most diluents, spilled individually or in combination; while Tarmac looked hard at mix design, to eventually arrive at Mastershield, a surfacing process incorporating the new binder.
Assessment techniques had to be devised to ensure that both the binder and the surfacing process actually worked. No established tests for fuel resistant binders exist: 'We had to devise our own tests in-house, using our own labs and knowledge from wherever we could find it,' Lancaster says.
Tarmac has just launched Mastershield commercially; Nynas in turn will be offering Nyguard to other approved asphalt manufacturers which want to take up the opportunity. 'We expect the marketplace to take up the process with enormous enthusiasm,' says Lancaster.