Roads and pavements: New from old

The construction sector is particularly material-intensive: every year around 27 million tonnes of cement and approximately 42 million tonnes of steel are needed to build new buildings, roads and other infrastructure such as bridges, railway tracks and so on. At the same time mineral construction waste is one of Germany’s largest waste fractions. Both the national sustainability strategy and the government’s resource efficiency programme ProgRess have a target of doubling resource productivity by 2020. For the construction sector that means high-quality recycling for the waste as far as possible.

At present an estimated 40 million tonnes of mineral demolition waste is already recycled annually in road building, corresponding to more than half the waste generated. By comparison, 130 million tonnes of primary raw materials are used in road building every year. In a current project for the German Federal Environment Agency, the Oeko-Institut and the Institute for Energy and Environmental Research (IFEU) in Heidelberg have now systematically evaluated the amounts of waste and recycled material arising from road and pavement building. Firstly, projections had to be produced for the amount of future waste and the demand for construction materials for the sector. Secondly, it was essential to assess the proportion of these waste materials that can be reused in the road and pavement network and the share of the overall demand for construction materials they can meet.

Replacing primary raw materials in road and pavement building

To determine future demand for road-building material and the potential for recycling construction materials, the project team first carried out a comprehensive and precise analysis of the road network and the stock of material that this represents – down to district level. To do this, they created a database using geoinformation from ATKIS (Amtliches Topographisch-Kartographisches Informationssystem, Authoritative Topographic-Cartographic Information System), searches via the construction work databases of the federal states and a survey of 300 local authorities.

The analyses show that, at 18,000 kilometres, Germany’s motorway network is more than six thousand kilometres longer than figures usually show. In total, therefore, the road network consists of 41,000 kilometres of major national roads, 87,000 kilometres of main roads and 92,000 kilometres of minor roads. Altogether these roads contain 2700 million tonnes of unbound layers (frost protection, gravel and crushed stone), 1600 million tonnes of asphalt, 310 million tonnes of concrete and 110 million tonnes of cobblestones. Bridges and tunnels account for more than 152 million tonnes of concrete and approximately 25 million tonnes of steel.

Scenarios for road-building resource demands

Building on this, the experts developed scenarios for the future expansion and maintenance of the road network. They conclude that almost 45,000 kilometres of new roads will need to be built by 2030 and a large part of the whole network more or less completely repaired. However, they also found that in theory more than half the demand for construction materials of all types can be met through demolition waste. Thus 28 million tonnes of asphalt could be reused as aggregate compared with the 12 million tonnes used in 2014. There is also a future need for almost 12 million tonnes of concrete annually until 2030. Furthermore, the recycling quotas could be increased further with the right incentives, so that up to two thirds to three quarters of the demand for construction material could be met through recycling.

Recycled building materials: Economic and environmental advantages

The Oeko-Institut project makes it clear that reliable statistical records are needed for construction waste. At present the statistical data is unreliable and in some cases difficult to decipher. For example, construction waste only appears in the statistics if it leaves the construction site. Most of it is used in the base layers of roads, meaning that valuable materials are lost for closed-loop uses.

Overall the findings show that substantial material streams can be recovered from road and pavement building and put to further use. Recycling presents an opportunity for high-quality re-use of building materials, on both environmental and economic grounds. Realistic pricing is necessary for this potential to be realised. Only if the costs of primary materials rise, whether through more limited availability of finite resources (such as bitumen) or by means of actively influencing prices, for example through taxes, do recycled building materials become economically more interesting. Then longer transport distances or alternative procedures for processing waste building materials close to the site become worthwhile as well.