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Sustainability - 27.06.2024

Towards a Circular Economy in Construction: Understanding Sustainable Concrete

Eine Frau mit langen, glatten braunen Haaren, die einen grauen Blazer über einer marineblauen Bluse trägt, lächelt in die Kamera vor einem schlichten hellgrauen Hintergrund.
Author
Lisann Hessel-Matusek

In the construction boom of recent years, the urgency to reconsider resource consumption and the environmental impact of the construction industry has increased. While new living spaces are being created, the environment and the habitats of numerous animal and plant species suffer from ongoing raw material extraction and consumption. However, this challenge also presents an opportunity: the circular economy.

What is the circular economy?

According to the European Parliament's definition, the circular economy is a production and consumption model that aims to use existing materials and products for as long as possible through sharing, reusing, repairing, refurbishing, and recycling. This approach extends the life cycle of products and minimizes waste, as resources and materials largely remain in the economy after a product’s life and are reused repeatedly.

This stands in contrast to the linear economic model, which relies on large quantities of cheap, readily available materials and energy.

The concept of the circular economy can also be applied to the construction sector — for example, through the use of recycled concrete.

Graphical representation of the circular economy
The circular economy extends the life cycle of products.

Conventional concrete and the specially developed "recycled concrete"

The Status Quo – Conventional Concrete

Conventional concrete has been an essential building material worldwide for over a thousand years. Its durability and versatility make it the first—and often the only—choice for many construction projects. However, conventional concrete production requires significant energy, generates substantial greenhouse gas emissions, and impacts ecological habitats through the continuous extraction of sand and gravel. Given these challenges, it is crucial to explore and promote alternative approaches, such as recycled concrete, to enable a more sustainable future for construction.

Our Specially Developed Recycled Concrete

As part of the EU-funded CIRCuIT project, OTTO WULFF collaborated with EGGERS Tiefbau, OTTO DÖRNER, eHoch3, TUHH, and the Senate Chancellery of the Free and Hanseatic City of Hamburg to address the challenges of conventional concrete. Together, they developed a new formula for producing recycled concrete.

Four years of intensive research went into this specially developed recycled concrete, which was used for the first time in a school construction project in Hamburg in February 2024.

Facts:

The circular economy is a production and consumption model that seeks to keep materials and products in use for as long as possible through sharing, reusing, repairing, refurbishing, and recycling.

The challenge of using recycled concrete

In addition to the advantages of recycled concrete, we as a construction company also face challenges when using the “Hamburger Mische.” As the first in-situ recycled concrete made entirely from 100% recycled material, it falls outside the applicable standards. This means that approval must be obtained on a case-by-case basis for each construction project. An application for the use of this unregulated building material must be submitted to the authorities, and extensive testing along with an expert opinion is required in advance to demonstrate suitability or equivalence. While the authorities’ testing costs are manageable, they are typically in the five-digit range.

Another challenge is sourcing the demolition material required for producing recycled concrete. Regional and geological variations mean that the aggregate and other components can differ significantly. Additionally, pure, selective, and economical demolition usually requires space for storage, sorting, containers, and construction machinery, as well as suitability of the building to be demolished—conditions that are often difficult to meet in inner-city locations.

Despite these challenges, the potential of recycled concrete as a sustainable building material is enormous and represents an important milestone toward a more circular economy in the construction industry.

Insights from Frank, Senior BIM Manager at OTTO WULFF:

Portrait of Senior BIM Manager Frank
Senior BIM Manager: Frank

1) As part of the EU research project CIRCuIT, you were involved in the further development of the "Hamburg mix." What technical properties does recycled concrete or the "Hamburg mix" have compared to conventional concrete, particularly in terms of strength, durability, and resistance to environmental influences?

Concrete is produced specifically to meet certain requirements. In this respect, the "Hamburg mix" serves as an alternative ingredient for a concrete recipe. Compressive strength, durability, and resistance can be adjusted for recycled concrete according to the recipe. Some compromises may be necessary in terms of deformation stress. On the other hand, the mix allows for excellent exposed concrete surfaces. Recycled concrete should, however, be used only to a limited extent when exposed to the elements.

2) Are there certain construction projects for which the use of the "Hamburg mix" is particularly suitable?

The "Hamburg mix" is suitable for all construction projects requiring high-mass components. Its applicability depends on the component rather than the project or location. Like standardized recycled concrete, the "Hamburg mix" can be processed identically to conventional concrete.

3) How does the use of recycled concrete affect the overall ecological footprint of construction projects?

Recycled concrete is only one component in assessing the sustainability of building materials and construction projects. In many cases, there is no alternative to concrete, and sometimes it is even the better choice. Nevertheless, reducing concrete use wherever possible is crucial, as the CO2 emissions from cement production are difficult to lower significantly. We have long been using cement with the lowest CO2 emissions, not only for the "Hamburg mix." In other aspects of the life cycle analysis, however, using recycled materials in concrete has a clearly positive impact. Achieving more than 100% replacement of sand and gravel, as in the "Hamburg mix," is not possible in terms of reuse. However, combining it with alternative binding agents is technically feasible, and we have already explored this option.

4) Can you give us an assessment of what would need to change in the future so that the use of R-concrete is no longer an exception?

With the model building and the school building on Richardstraße in Hamburg, we have demonstrated that the proportion of recycled materials in concrete can be maximized without compromising quality or the construction process. This helps build trust. Additional costs are manageable, and there are no objective reasons against recycled concrete. Our practical examples have already convinced some stakeholders. Moving forward, we need a market that actively demands and uses recycled concrete on a large scale, particularly with 100% recycled material. It would also be helpful if the underlying standards for concrete recipes were updated quickly, so individual approvals would no longer be required for every construction project using the "Hamburg mix."

Note on Translation:
This text was automatically translated from German into English. We try our best to make it accurate, but occasional errors may happen. Please refer to the original German version for the most reliable information.