Can excess soil from construction be used as a sustainable alternative to traditional building materials like concrete and other CO2-heavy materials? This is what Danish architects and engineers are working to find out.
Among the initiatives is the Clay Alliance (Leralliancen) partnership, which explores the possibility of using rammed earth as an alternative to materials like concrete. The goal is to help reduce the climate footprint of the construction industry and gather knowledge about new construction methods, tells Ida Bertelsen, Assistant Professor at DTU Sustain and sparring partner in the partnership together with Professor Per Goltermann from DTU Construct.
"I believe in clay and that it can help shape our future. I think we're currently riding a wave of focus on meeting CO2 requirements for buildings. We also see that clay soil is good for regulating the humidity in homes and ensuring a more stable indoor climate—both in terms of humidity and temperature. But I also find it exciting to investigate the addition of natural materials such as fibres and biopolymers, the latter improving durability, which is the biggest challenge for building materials in unfired clay soil," says Ida Bertelsen.
Residual fibres from food and agriculture
Using soil as a building material is not a new invention. Clay soil has been used to build houses for centuries. In Denmark, clay soil and burnt lime have also played a major role in Danish building traditions—including the construction of many of our half-timbered houses.
But while the Danes forgot about building techniques when concrete became the new building material, Southern Europeans have held on to the old building traditions. Germany and Austria have also continued to build with clay soil, and today you can see apartment buildings built with rammed earth. On this background, several student projects at DTU will conduct full-scale tests of unfired clay walls, which will contribute to designing rules and standards for the load-bearing capacity of the walls.
More projects in pipeline
Today, several tests of clay soil with different types of additives are being conducted at DTU—each project with its own focus.
Among the experiments in DTU's materials laboratory is a student project on using residual fibres from the food and agricultural industry, for example from biogas plants and grass protein plants.
In another research project with the COWIfonden, DTU researchers are investigating clay from different locations, the addition of lime and cement, long-term durability, and recycling of stabilized clay soil. A third research project with the Danielsens Fond foundation investigates the addition of natural polymers to clay soil as a sustainable alternative to, e.g., lime and cement. Polymer is a substance made of molecules containing a large number of iterations of one or more types of atoms or atomic groups. Finally, DTU participates in a Horizon Europe project called AshCycle. Among other things, the researchers are investigating whether sludge ash can be reused to stabilize unfired clay bricks.
