Towards circular construction

Property developer Olav de Linde is building an orangery of 180 m²made of reused building materials on parts of the old postal terminal at Ankersgade in Aarhus. He is doing this to show that it can be done—and to learn from the challenges it presents when the proportion of reused materials is to be as high as possible.

The materials are almost 90 per cent reuse from the Aarhus property. For example, doors and windows are from the old psychiatric hospital in Risskov, the timber is from Chokoladefabrikken (the Chocolate Factory) in Klostergade, the floor and ceiling from Aarhus Municipal Hospital, and the iron beams come from the housing development SHIP in the urban area of Aarhus Ø. Olav de Linde finds other materials in his own warehouse, located in an old shipyard on the Port of Aarhus. Here he stores everything from used bricks to wooden beams and old iron from old industrial buildings that he has renovated.

The orangery is just one of many buildings that Ejendomsselskabet Olav de Linde is constructing using almost exclusively reused materials. Over the years, the company has renovated and preserved more than 300,000 m² of property in Aarhus, Odense, and on Zealand using reused materials.

“We’re building using reused materials because we like it and because we think it’s the right thing to do, and people like living in houses with soul and charm.  But it takes creativity. We want to reuse as much as possible, but statutory requirements and certifications make it difficult to go as far as we would like. This makes it difficult to build sustainably,” says Olav de Linde. 

Pilot projects show the way

Like other developers, architects, and engineers, Olav de Linde is experimenting with reuse and recycling of construction waste and is pushing the envelope for what is possible.

Experience and data from pilot projects like the orangery are currently leading the way to a circular construction economy. This is shown in a sector development report from DTU, which points out that the industry lacks harmonized standards and technical solutions for large-scale reuse of old building materials. Lisbeth Ottosen is one of the authors of the sector development report. She is Professor of Sustainable Building Materials at DTU and conducts research into reuse of building materials and use of waste in the production of new building materials.

“I experience that there is great focus on reusing building materials, but it isn’t all that simple. When you’ve used the materials once, they’ve become unique and have been exposed to different conditions. They may have been located outside under various degrees of protection or have been subjected to different physical strains. Therefore, we have to assume that all materials are different. That makes it hard to reuse them. Especially when it comes to reusing materials for load-bearing structures. This requires documented quality. We’re not yet able to do this,” says Lisbeth Ottosen.

She currently heads a large Grand Solutions research project (see fact box) called BusinessReuse, in which DTU and a number of industrial partners are developing methods for testing and documenting the quality of reused building components such as concrete, steel, and wood.  This is done using so-called non-destructive test methods, where researchers measure the properties of the construction materials without changing them.

One of the methods involves sending an ultrasonic pulse through the materials. Here, the researchers analyse the signal from an ultrasonic meter and assess whether the materials can be reused. Non-destructive test methods differ from conventional methods where destructive tests are performed on samples. This can, for example, be done by measuring how much the materials can tolerate being compressed without breaking, or by testing how they react during a simulated fire. Such tests result in the destruction of most of the material.

“There are already a large number of non-destructive testing methods on the market, but using them to assess the quality of reused building components is a new approach. In the research project, we’re therefore examining how far we the existing methods can take us. We hope that the project can lead to joint standards we can apply to reuse of load-bearing structures. This will make it easy and safe for the construction industry to choose reused materials,” says Lisbeth Ottosen.

Common European standards

The test methods developed in the research project constitute a Danish contribution to the development of common European standards in a new European Committee, Comité Européen de Normalisation (CEN). Danish Standards—Denmark’s standardization organisation—has been appointed by CEN to manage, develop, and run the committee.

As part of the work, a European working group has been set up, and Lisbeth Ottosen has been appointed as head of the group.

The aim of the committee’s work is to promote the transition to a circular construction economy through common procedures, language, and definitions, says Charlotte Vartou Forsingdal, Senior Consultant at Danish Standards:

“When Denmark takes the lead in this area, it means that we’re at the forefront of developing the common European standards that will set future market requirements and shape the greener market of the future. This can help strengthen the development of the construction industry by giving Danish companies an edge and helping to scale good Danish solutions to the rest of Europe.”

According to Charlotte Vartou Forsingdal, the common European standards can also help counter scarcity of materials in the construction industry.

Construction industry impacts the climate

In Denmark alone, the construction industry accounts for almost 35 per cent of all waste in Denmark—equal to 4.1 million tonnes of waste annually. In addition, new construction and renovations of homes account for about 20 per cent of total carbon emissions. Globally, the construction sector is expected to generate 2.2 billion tonnes of waste by 2025.

The waste comes from a number of sources, including the production of building materials and demolished buildings. Construction waste is often not reused. However, several of the materials are recycled or utilized. Biobased materials are converted into energy by combustion, metal is remelted and used in new goods, and heavy materials such as concrete and brick are crushed and used as—for example—a base layer under roads.

But it is not enough simply to utilize building materials, according to Lisbeth Ottosen. It is also about reusing materials so that you actually use a wooden rafter as a wooden rafter in a new construction.

“We’re good at utilizing, but not at reusing. It’s a matter of opinion whether it’s best to tear down a building or keep it. Sometimes you have to demolish it if it’s obsolete or to construct a new building. But—from a resource perspective—it’s often best to keep the building and renovate it. This reduces the drain on our natural resources and carbon emissions,” says Lisbeth Ottosen.

She points out that there is no tradition for reusing waste as a resource. But if we are to meet the target of reducing our carbon emissions by 70 per cent by 2030, this can only be done through a holistic approach to construction:

“Construction is incredibly linear. But this isn’t sustainable. We use more resources than the Earth can regenerate. And based on an expectation of an ever-increasing global population—combined with a growing global middle class—this necessitates more construction. Already now, we have a massive overconsumption of resources, so I dare not even think about what the situation will be if we continue to build like we do today. In my opinion, circular construction is an essential piece of the puzzle, but we need to do even more. Maybe we’ll have to build fewer houses and live in smaller homes.”

New methods for reuse

Until we crack this problem, we are working hard to find new solutions. Although we have only just started reusing materials in Denmark, we are well on the way with recycling materials (see fact box on the difference between recycling and reuse).

At DTU, research is being conducted into a number of aspects, including new methods for recycling waste in new building materials. For example, researchers are studying how to clean toxic residual waste—such as fly ash and mining waste—so that it can also be recycled in cement and concrete. This can contribute to reducing carbon emissions. In fact, concrete is the big culprit in the climate accounts of building materials, not least because cement is an important ingredient as a binder in concrete, and cement production leaves a big climate footprint. In another project, researchers are studying how to recycle old fishing nets as reinforcement in new building materials.

Among the industrial research projects, other research groups at DTU are working with the construction industry to develop a tool for performance of absolute sustainability assessments. Here, it will—for example—be possible to calculate what it means to the individual construction project to comply with the goal of the Paris Agreement to limit global warming to 1.5°C. In another industrial research project, a tool is being developed to assess how circular construction projects support the UN 17 Sustainable Development Goals.

Back in Aarhus, Olav de Linde also wants to share his experience with the construction industry. If he is to give some sound advice, it is as follows: Plan well in advance and be creative.

“You may find some timber or steel by phoning various suppliers. But if you need to reuse materials on a large scale, it’s difficult to locate large quantities of materials for reuse. It's about thinking carefully, buying materials well in advance, and stocking them until you need them. Otherwise, you’ll only have enough to build a chicken coop,” says Olav de Linde.