Using R-Concrete for Circular Value Creation - Opportunities & Obstacles

The fourth station of the Zirkel.Training was all about a future-oriented building material: R-concrete (resource-saving concrete). The civil engineer Prof.’in Dr.-Ing. Sabine Flamme from Münster University of Applied Sciences and her two guests from the entrepreneurial practice illuminated the material and its opportunities for the Circular Economy from various perspectives. Our first hybrid event with about 25 students in the lecture hall in Münster and 20 participants connected via Zoom also went smoothly from a technical point of view.

High share of the construction sector in resource consumption

In her introductory speech, Prof. Dr. Sabine Flamme first made clear the high relevance of the construction sector in terms of resource consumption and waste generation. In Germany, it accounted for 60 % of total resource consumption and 52 % of waste generation in 2020. Only a negligibly small proportion of demolished buildings currently ends up back in concrete (less than 1%), and the majority of recycled building materials are used in road construction.

But what exactly is R-concrete? Concrete is a mixture of water, cement, admixtures, sand and gravel. R-concrete differs from conventional concrete only in that parts of the natural aggregate in the form of gravel are replaced by recycled aggregate, i.e. crushed demolition material. The requirements for the concrete are identical in both cases and are regulated by DIN standards and guidelines.

How much is required for the production of R-concrete is already decided by the organization and quality of the demolition of buildings. Once interfering materials and non-mineral components have been removed, a quality control follows before the recycled material can be mixed with the other ingredients to produce new concrete.

A recent example of the use of R-concrete is the town hall building in Korbach, where it was possible to reuse 62% from the demolition of the 1970s part of the building in the new construction; of this, 15% in turn went into the production of concrete.

Economic, technical and legal aspects

Alexander Henksmeier, raw materials and industrial engineer and concrete technologist, explained in his paper favorable factors and obstacles for R-concrete with a view to the East Westphalia region.

There, long approval procedures and high environmental regulations mean that it is becoming increasingly difficult to extract sand and gravel, which are used as natural aggregates in concrete. The alternative transport of gravel over longer distances, on the other hand, is expensive – which makes the admixture of recycled material more attractive, both financially and ecologically.

On the other hand, a close look at the regulations and requirements shows the extensive quality controls and tests that the building material must pass. Moreover, R-concrete is not approved in Germany for all building areas and functions; for example, it may not be used outdoors, where it can come into contact with chlorides or de-icing agents.

But it is not only technical hurdles that the building material has to overcome. A lack of acceptance on the part of building owners is also currently still standing in the way of its wider use.

A good step forward: Switzerland

In the third presentation, Patrick Eberhard, co-owner of a large manufacturer of recycled building materials, provided insights into the status of R-concrete in his home country, Switzerland. Eberhard’s company has been selling R-concrete since 2003, and it has been used in about 100 buildings. For Patrick Eberhard, one thing is clear: an old house must become a new house again.

Some framework conditions in the neighboring country favor the spread of R-concrete; among other things, a higher proportion of recycled material in R-concrete is possible, or admixture in a lower proportion is permitted even without a declaration. Primarily due to the targeted invitation to tender for R-concrete in public construction projects, R-concrete now has a share of 13% in Switzerland, which is significantly higher than in Germany.

Patrick Eberhard emphasized the need for innovations in the building materials cycle – and presented two at once: the robotized processing of construction waste and the company’s own product development zirkulit® Beton. The latter not only has a particularly high recycled content, but also acts as a CO2 reservoir.

Persuasion work to be done

In the concluding question and discussion session, it once again became clear what role building owners, especially the public sector, have to play in the dissemination of R-concrete. They have the leverage to increase demand. The fact that this is not yet happening to the desired extent is also due to the fact that R-concrete still has an image problem.

The experts agree that “recycling” is not a successful selling point for R-concrete, as it is often associated with inferior quality. Better arguments are rather the conservation of resources and – as in the case of zirkulit – the CO2 storage capacity.

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