“As engineers, we are part of the problem, and therefore we should also be part of the solution,” says Isabell Spang Andersen.

In January, she received the prestigious JCN Housing Award for the best Master’s thesis of the year among civil engineering students. The award is presented to students who, through “high academic standards, courage and innovation, contribute to developing the construction industry of the future.”

And it is precisely the construction of the future that lies at the heart of Isabell Spang Andersen’s thesis. In it, she investigates one of the most pressing questions facing the construction sector:

How can resource consumption and CO₂ emissions from concrete construction be reduced without compromising safety?

In her thesis, she explores how an algorithmic approach can be used to reuse load-bearing concrete elements in combination with new elements in multi-storey buildings.

The method functions as a planning tool that matches reclaimed and new components, identifying the optimal configuration based on requirements for structural strength, cost, and carbon footprint.

The calculations show that a significant proportion of the load-bearing concrete elements – in some cases up to two-thirds – can consist of reused components without compromising safety.

At the same time, the results indicate that the method can reduce costs, material consumption, and CO₂ emissions.

The model thus makes it possible to work systematically with reuse at scale and to predict how much can realistically be reused in a specific construction project.

Reuse need not be all or nothing

It is now widely recognised that the construction industry places a heavy burden on the climate. In fact, it accounts for approximately 30 per cent of total CO₂ emissions in Denmark.

At the same time, urbanisation continues unabated, and pressure on the housing market is increasing in the larger cities.

However, Isabell Spang Andersen has approached the task of finding a climate-friendly solution with a clear-eyed understanding: she recognises that reuse solutions are often associated with higher costs than new materials. Nevertheless, she is keen to help accelerate the green transition.

“A hybrid approach could solve many of the challenges,” she says.

At present, it is difficult to envisage a construction industry based solely on reuse. But even partial reuse represents a meaningful step forward.

“It is in fact technically feasible to incorporate reused concrete elements, as they can last for many years. Buildings are often demolished due to changes in socio-economic conditions – not because they are no longer safe,” she explains.

This means that many buildings are, in practice, removed long before their technical service life has expired.

An interest in more climate-friendly construction methods has followed Isabell Spang Andersen throughout her studies, where questions of resource consumption and material durability have gradually become more prominent.

By reusing materials that still retain value, she argues, it is possible to create a more circular flow in construction and extend the service life of materials.

“The best option is to use what you already have. The second-best is refurbishment. The third-best is to dismantle buildings and reuse the elements. In some cases, they can be reused as they are; in others, they may require some upgrading,” says Isabell Spang Andersen.

A lack of standards is holding back reuse

Isabell Spang Andersen believes that the construction industry still lacks common standards for how materials can be reused in a way that is safe, efficient, and economically viable.

When reuse is not an established standard, uncertainty often becomes too great.

For many in the industry, the risks associated with building with reclaimed materials – which may not perform as expected, may fail to meet safety requirements, or may ultimately prove more costly – outweigh the benefits of reducing the carbon footprint of construction.

In her work, Isabell Spang Andersen has, among other things, looked to Norway, where standards have already been developed for how building materials can best be dismantled, handled, and integrated into new structures.

However, the Norwegian experience cannot be directly transferred to Denmark, as both building regulations and construction practices differ. It is precisely here that she sees potential in her own tool.

The hope is that it can become an operational tool that makes it easier for industry stakeholders to work with reuse in practice – thereby lowering the barrier to choosing reclaimed materials over new ones. She hopes that more stakeholders in the industry will recognise the potential and dare to be more ambitious.

“Since the award was announced and attention was drawn to my work, I have received several enquiries from people in the construction sector who would like to learn more about the project and read the thesis. I see this as very positive, as it demonstrates a genuine interest in the industry in reusing concrete elements – and that we are moving in a positive direction in the green transition.”