On the floor of DTU’s materials laboratory are big bags full of clay soil. In this laboratory, researchers and students conduct research into building materials. Here we meet the two students Rasmus Asbjørn Høy-Pedersen and Mads Dalby Kamper, who study Architectural Engineering at DTU.
They are among a group of around 30 project students at DTU who—over a four-year period—have tested the strength and composition of clay soil and investigated how the soil reacts when they add lime, for example. This is done under the guidance of Assistant Professor Ida Bertelsen, who heads many of the student projects together with her colleagues.
The trials will teach them how to use surplus soil from construction sites to build clay soil noise barriers along highways. The idea is to reuse the clay soil where it is dug up. It will reduce soil transportation, CO2, noise, and particle pollution.
Every year, around 15 million tonnes of surplus soil is transported away from building and construction sites in Denmark. At the same time, the construction industry lacks raw materials like sand and gravel to produce concrete.
“We need to think creatively if we are to reduce the carbon footprint of construction. But there’s no way around it. There is a need to develop new alternative materials and recycle building materials. One way is to replace CO2-heavy materials like concrete with surplus soil from construction projects. It can play an important role in reducing construction CO2 emissions,” says Ida Bertelsen.
Danish Road Directorate: Great perspectives
Behind the development project, which is funded by the Capital Region of Denmark, is DTU together with the Danish Road Directorate and a number of private partners. The four-year project ended in December 2024. But research continues. The results are promising and the noise barriers are in high demand.
Among those who see great potential in using sustainable noise barriers is the Danish Road Directorate. They need more climate-friendly alternatives to traditional noise barriers—which typically consist of CO2-heavy materials such as steel, aluminum, concrete, mineral wool, and plastic.
In 2024, the Danish Road Directorate was the first in Denmark to tender a noise barrier made of lime-stabilized clay soil along Storstrømsvej on Falster in connection with the new Great Belt Bridge. The method involves stabilizing the clay soil with a few per cent lime to increase its strength and resistance to water.
And even though the clay soil noise barrier was rejected as the development project was not completed at the time of the tender, the Danish Road Directorate is confident about the future of lime-stabilized noise barriers. This is according to Road Directorate consultant Jan Aagaard:
“With the tender, we signalled to the industry that we need more climate-friendly solutions such as noise barriers made of lime-stabilized clay soil, which we see great opportunities in constructing. Now the manufacturing technique needs to mature for production, which hopefully happens before long. In addition to being new and innovative, the noise barriers will contribute significantly to reducing the CO2 impact of construction projects while conserving natural resources.”
Testing for wind and weather
Back in the materials lab, Rasmus Asbjørn Høy-Pedersen and Mads Dalby Kamper explain how they mix, produce, and test the clay soil that is the main ingredient in the noise barriers. The soil samples come from different locations, and each soil sample has its own characteristics. So a lot of tests are carried out, but the approach is the same.
When the clay soil is delivered to DTU by large trucks, it is initially divided into smaller portions and dried in a large oven for three days. Students then experiment with several techniques to produce cylinders, cubes, and blocks of clay soil with the addition of lime—from compressing layers of clay soil with a vibratory plate compactor for structural parts to squeezing clay through a steel profile for giant blocks.
The samples are both pressure-tested and exposed to the elements to see how resistant they are. This takes place both inside the materials laboratory and outside, where demonstration walls have been built at DTU and in Landerslev south of Jægerspris. When that work is finished and all the data is analysed according to Professor and Head of Studies Per Goltermann, who helps to guide the students. He further explains:
“The project has shown that clay soil has huge potential. But we couldn’t have come this far and achieved such great results without close collaboration with industry and our many students. It’s a tremendous boost to our capabilities. It also means we can offer students project experience and learning that they can’t get anywhere else.”
Pioneers of sorts
For Rasmus Asbjørn Høy-Pedersen and Mads Dalby Kamper, being part of the development project has been educational. Here they have acted as pioneers of sorts—both creating new guidelines for clay soil testing and optimizing different methods—which has given them a great deal of knowledge about building with clay soil.
Therefore, they continue with the laboratory studies as student assistants, and in the spring they will write their master’s thesis on statics in unfired clay walls, says Mads Dalby Kamper:
“Participating in the project has been exciting because clay soil is a material that we have a lot of and that we don’t utilize as much in the traditional construction industry. I’m hopeful that we can use the clay soil for many applications and that there can be a shift in what materials we will use in the future. Ok, so we’ll probably not be building 20-storey high-rise buildings out of clay soil, but if you can replace a lot of concrete with clay soil in smaller buildings, I guess it’s a start.”
Read: Clay and soil make comeback
