Of all the things to try to recycle, concrete might be one of the hardest – but now Austrian researchers have come up with a new method that promises much greater ease and uptake. 

Previously, materials made from recycled aggregate – instead of natural gravel – were usually too weak and porous for use, but this new recipe is allowing recycled concrete to be put to work on bridges and buildings.  

"We are adding crushed concrete that we got from a demolished construction site," says scientist Bojan Poletanovic, while showing CGTN how the project's new concrete is made. 

Together with industrial partners and public funding bodies, the Vienna university team spent four years working on a new recipe – adding other components and switching around the mixing stages. 

"So far, recycled aggregate concretes were used just in low-grade applications," says Ildiko Merta, professor of civil engineering at TU Wien. 

"Now with the new recipes, we will be able to use this concrete also in bridges, or like columns in buildings."

Green trend

It's part of a green trend, as more and more recycled materials are making their way onto construction sites. Some concrete mixtures even contain incinerated household or business waste.

In Vienna, recycled concrete is not only being used to build houses, but also to enlarge the metro network. A new line is set to have emergency exits made from recycled materials.

One remaining challenge is transportation. Demolished concrete is often sent to distant crushing sites, before being sent out to building sites again.   

"Recycled aggregate concrete is only then sustainable if you can produce concrete on the demolition site," says Merta.

To move toward this, some companies are starting to use mobile crushing machines directly on demolition sites to improve sustainability.

Meanwhile, following their research, the university team is urging Austrian authorities to raise the permitted amount of recycled aggregate in concrete from around 30 percent to at least 70 percent… helping the construction industry to put green issues at its core.