Recycled concrete: an important contribution to the circular economy
March 18 is World Recycling Day. Reuse is also an important strategy in the concrete industry, primarily to reduce the use of materials. Current projects from the infrastructure and building construction sectors show how concrete demolition can be turned back into new, high-performance building material.
Every year, around 100 million tons of construction raw materials such as sand, gravel, grit, crushed stone, clay and natural stone are required in Austria. The domestic construction industry accounts for 80% of this. In order to use the available resources responsibly, the Austrian concrete industry relies, among other things, on recycled concrete, which uses recycled aggregate instead of primary material. At present, the quantities of recyclate currently available only cover around 9% of the aforementioned annual demand.
Concrete can always be reused
"Due to its composition of natural raw materials, concrete can always be dismantled, processed and reprocessed into recycled concrete. This makes it ideal for keeping it in the cycle," explains Christoph Ressler, board member of Beton Dialog Austria and managing director of the Quality Association for Ready-Mixed Concrete. "This is also shown by the high recycling rate of our building material. Less than one percent of used concrete is currently sent to landfill." According to the latest status report on the Federal Waste Management Plan (figures from 2021), only 0.4 percent of the approximately 4.5 million tons of demolished concrete was sent to landfill. Almost 100 percent was therefore recycled. Here are two examples of the use of recyclate.
Vienna's public transport lines switch to recycled concrete
Wiener Linien is using recycled concrete in various underground and above-ground construction projects. The company is testing the use of different recycled aggregates in the U2 tunnel together with concrete manufacturer Wopfinger Transportbeton and the Research Institute of Structural Engineering (IKI) at the University of Natural Resources and Life Sciences Vienna. An innovative reinforcement that requires less material is also being tested in this subway project.
In the superstructure sector, Wiener Linien is working with partners from industry and research to explore ways of reusing concrete slabs and concrete formulations with low-emission cements. According to a study by Wiener Linien, this involves large quantities: Wiener Linien's current 600,000 track support slabs cover an area of approximately one million square meters and correspond to a weight of around 375,000 tons. If the track base plates currently in use were replaced by plates made from recycled concrete, the proportion of recycled material could be up to 50 percent, according to the DIN EN 206 standard cited in the study.
Recycled concrete sets a precedent
Two construction projects from Salzburg also prove that recycled concrete works. When renovating and extending the Anif elementary school, the non-profit developer Salzburg Wohnbau used the old building stock as a raw material store. According to the developer, a total of 1,600 tons of recycled concrete was used, around 32 percent of the entire in-situ concrete. A recipe for success that is already setting a precedent in Salzburg.
According to Salzburg Wohnbau, 1,000 tons of old concrete from the A10 motorway will be used in the expansion and renovation of the Adnet elementary school and 35 tons of CO2 will be saved during construction, including through the use of clinker-reduced cement. The project will be completed in 2025.
Use fewer raw materials, reuse and recycle
The use of recycled concrete in Austria currently still depends on availability and demand. Conserving these resources through reuse and recycling promotes circular construction and helps the climate. There is an urgent need to conserve natural resources by using building raw materials more sparingly overall and massively increasing the proportion of recycled materials.
