Funded by WRAP (the Waste & Resources Action Programme) and undertaken by C4S, part of TRL Limited, the study concludes that, although there are significant quantities of concrete and asphalt at abandoned airfield sites across the country, the amount that could be recovered in practice would not make a significant contribution towards existing mineral planning targets for aggregate provision. However, it does identify five major airfields in the East of England where recycling the air strips could be economically and environmentally beneficial, particularly as they are situated in areas with the least permitted reserves of crushed rock.
WRAP says the research was necessary to ascertain to what degree disused airfields around England could provide a vital source of high quality recycled aggregates, thereby helping English regions to quantify the potential of this more sustainable resource in fulfilling their planning and development targets.
“Reserves of crushed rock in England vary from region to region and this often necessitates the transport of rock to areas where development is planned, but natural resources are low,” explains John Barritt, Technical Advisor to the Aggregates Programme at WRAP.
“As airfields are dispersed across England, there is an opportunity to recycle the concrete and asphalt runways to provide recycled aggregates in regions with limited reserves. WRAP funded the research to see just how practical it would be in reality, and if the quantities available were significant in the context of total aggregate demand.”
Wartime pavement quality concrete is generally very clean and of prime quality, and some contractors and aggregate suppliers already actively seek out opportunities to reclaim concrete and bituminous materials from old airfields. The materials can easily be reused as type 1 sub-base in accordance with the Highways Agency’s Specification for Highways Works, which allows 100% recycled aggregate with a recycled asphalt content of up to 50% and therefore negates the need to separate the recycled materials. Nevertheless, segregation is feasible for a number of structural uses in concrete and asphalt if required.
The potential is significant: based on a concrete density of 2.4kg/m3, a single runway of 2000m in length and 45m width constructed with 300mm concrete contains around 64,800 tonnes of potentially reusable material. An airfield generally has at least two runways, plus taxiing and parking areas.
The research ascertained that not all of England’s 688 inactive airfields are suitable for recycling in practice. Some have been put to other uses, such as industrial parks, residential developments or leisure facilities, while others have had their air strips incorporated into the local road infrastructure or removed altogether. In addition, some have become heritage sites with listed buildings, museums and memorials so removal of the concrete air strips would not be appropriate. Other sites are so small that recycling would be uneconomic.
There are other barriers too: planning consent to recycle in situ can be refused on the grounds of noise and dust, particularly if the site is close to housing. The need to make provision for the disposal or treatment of associated substances, such as tar, asbestos, underground fuel tanks and contaminated soil, plus the potential for unexploded ordnance, can also make recycling concrete runways a less attractive option.
Taking these factors into account, the research calculated that suitable disused airfields could potentially yield 9.5 million tonnes of concrete, plus one million tonnes of asphalt planings. Around half of this total would come from just five large airfields based in the East of England – and this could be significant.
The pattern of consumption for aggregates in 2006 and beyond will be driven by new major development areas (MDAs) which will require considerable aggregate resources for the construction of housing, roads and community facilities. The four major growth areas – Thames Gateway, Milton Keynes and South Midlands, Stansted and Cambridge and Ashford in Kent – are all situated in the East, in areas with the least permitted reserves of crushed rock.
The majority of airfields identified by the research are also located in the East of England and a number coincide with the MDAs. Although they do not contain quantities of concrete that are significant in terms of national and regional planning requirements (less that 1%), the research does conclude that disused airfields could represent an economic alternative to imported crushed rock at a local level.
The final report, An assessment of the potential of redundant airfields in England as a resource for recycled aggregates, contains full details about the potential uses of recycled concrete aggregates and recycled asphalt, the results of the airfield survey and an assessment of the potential markets for recycled aggregates – including MDAs and major road schemes – in England. It is available to download from AggRegain, WRAP's dedicated aggregates website.