High performance bitumen, cold mix/cold lay asphalt expertise and the latest in environmental engineering lie behind the Landrec process, a new way of cleansing brownfield sites. Resulting from an amalgam of technologies, Landrec has the potential to reduce substantially the amount of contaminated waste going to landfill.
The process works by coating granulated brownfield waste with a high- tech, cold mix bitumen emulsion to produce a stable asphalt suitable for highway construction. It puts potentially harmful substances to very good use, says general manager of Landrec, Dave Worrall.
'Our process is about applying a formula to soils and rubble which ends with their being coated and effectively neutralised. The end result is a construction material for roads and hard standings that is safe and robust - good for carrying heavy loads,' he says.
Landrec has its origins in a collaboration between two companies, environment specialist AEA Technology, the private sector offshoot of UK Atomic Energy Authority, and Aggregate Industries, best known through its Bardon subsidiary.
It was Bardon Aggregates that supplied the cold mix asphalt expertise - previously developed with bitumen specialist Nynas - that is the crucial part of the process. Asphalt is traditionally mixed and placed very hot but in recent years asphalt producers and their bitumen suppliers have been looking hard into the possibilities of cold mix/cold lay materials for use in road maintenance.
One advantage of cold mix/ cold lay is that heat plays no part in the mixing and setting, and the asphalt can be mixed and stockpiled before being placed. It retains its workability for a significant period.
Nynas developed a cold mix bitumen emulsion especially for Bardon.
The binder allows freshly mixed cold asphalt to maintain its mobility for some days before the material needs to be used. Once it has been rolled and properly compacted, the emulsion 'breaks' (that is, the water evaporates to atmosphere) and the asphalt cures.
'The technology is perfect for the Landrec process, giving us a substantial edge over any competitor offering to isolate contaminants with cement- based products. These harden as soon as they meet moisture and hydrate,' Worrall claims.
It means that Landrec can coat and mix polluted soil or contaminated construction waste, add additional aggregate if this is needed to strengthen the mix, then stockpile the asphalt for eventual use on site or transport it offsite for use elsewhere.
'The ideal is where the site developer has a certain amount of contaminated material which matches in volume terms road or car park material needed for the new development,' Worrall says. 'Then the cost of taking treated material offsite and disposing of it is removed; and the cost of mining and bringing in fresh aggregate is avoided.'
For any given brownfield site, the Landrec process begins with evaluation of any available data such as site investigations and chemical reports. Then the contaminated materials themselves are analysed.
Demolition waste has to be suitable for crushing and screening to below 50mm size. Soils have to be sorted out in terms of type - clays are the most problematic because of handling - and samples tested in Landrec's laboratory.
The exact formulae used to ensure that the end material is safe, whatever the form of contamination, is a commercial secret. When the calculations have been done and the treatment agreed, Landrec processes the granulated contaminated material to ensure every particle receives a thorough coating of bitumen emulsion.
Landrec's plant is mobile but hefty: sites to be treated have to be of a (fairly substantial) minimum size which would appear to rule out use of the process on small contaminated sites with, say, 100t of waste. 'This is a problem we are addressing in a cost effective way by establishing relations with operators of waste treatment and transfer plants,' Worrall says.
'The intention is for our plant to go to central waste centres where the developers of smaller projects can then access Landrec technology.'
The asphalt approach to treating brownfield sites comes out of the US and dates back a decade. Turning contaminants into usable construction material has become good business in America, with the process being used to treat contaminated soils where underground storage tanks have leaked and to provide wearing course material for car parks of substantial capacity. Well over 1Mt has been laid.
In Britain, Landrec has been demonstrating what can be achieved on some very high profile brownfield sites, including former gas works in east London.
One of Landrec's biggest jobs to date was helping clear up oil soaked sand following crude spillage from the Sea Empress off South Wales. Some 200t of this was processed and used as road base in a minor road near Fishguard. This road has subsequently been adopted by the local authority.
'Waste management licensing issues have to be addressed with considerable care,' says Worrall. The issues are highly complex and the properties of contaminated materials must be well understood and effective liaison with regulators is essential. 'Contaminated land equals public concern and lots of paperwork,' he says.
'People need to be convinced that the solution we offer is safe and permanent, but we are sure confidence will build in the short to medium term.'