Back to the future with wood and clay

It is well known that the construction industry contributes significantly to climate change with its massive greenhouse gas emissions. However, it is less clear how CO₂ emissions can best be reduced. The Innosuisse Flagship project (see box) Think Earth – Regenerative Building is taking a promising approach. Here, a large consortium led by ETH Zurich is focusing on modern construction techniques using timber and clay to reduce the environmental impact of the construction industry.

The combination of these environmentally friendly materials enhances their individual advantages: Timber provides the necessary load-carrying capacity and stiffness, while clay adds additional load-carrying capacity and mass, which contributes to heat regulation, vibration damping and fire safety. By 2029, efficient and scalable construction methods are to be developed in various sub-projects in order to advance climate-neutral construction and living.

With its Flagship initiative, the Swiss Innovation Agency Innosuisse promotes systemic and transdisciplinary innovations that are of central importance for the economic and social challenges in Switzerland. Unlike other Innosuisse projects, which usually solve specific problems of individual SMEs or start-ups, researchers from various institutions work together with numerous industry partners on an overarching issue. The Flagship project Think Earth – Regenerative Building comprises ten sub-projects ranging from materials science and process engineering to prototypes for building construction as well as case studies and standards for architecture. The aim is to lay the foundations for climate-neutral construction with hybrid elements made of timber and clay.

Although wood is a renewable natural resource, it must be reused if it is to be used sustainably in the construction industry. Currently, the reuse rate of wood is only 10 percent – as part of the Flagship project, this is to be increased to 90 percent with the help of other renewable materials such as earth-based building materials. Timber connections play an important role here. In contrast to concrete structures, which are cast as monolithic structures, timber structures rely on the connection of individual components. According to Empa researcher Pedro Palma, these are just as important as the timber components themselves and are often more critical from a structural point of view. “The connections ensure continuity and improve the structural behavior through various properties, such as the ability to deform and dissipate energy, that the wooden components themselves cannot offer.” In a sub-project, Empa's Structural Engineering Laboratory is working with researchers from ETH Zurich, Bern University of Applied Sciences BFH and 13 industrial partners on the disassembly and reuse of timber connections. At the same time, they are developing digital tools to support this process, thus strengthening circular economy.

Earth-based building materials have a good carbon footprint, and raw earth is available in almost unlimited quantities. However, they are often only used for smaller applications such as bricks, as their structure shrinks and cracks as they dry. According to Pietro Lura, Head of Empa's Concrete and Asphalt Laboratory and Professor at ETH Zurich, suitable additives are crucial to avoid this. “Clay can always be reused as long as it remains unchanged. However, as soon as a mineral stabilizer is added, the energy balance and recyclability deteriorate.” To solve this problem, researchers from ETH Zurich and Lura's team are working together with industrial partners BASF Schweiz AG and Eberhard Bau AG on bio-based and biodegradable additives. The researchers are testing their ability to reduce shrinkage while maintaining recyclability and water absorption. “The big challenge is to find functional additives that are both made from natural raw materials and biodegradable,” says Yi Du, researcher at Empa and ETH Zurich. The most promising additives are being tested on a large scale in order to use green chemistry to produce crack-free clay-based building materials and reduce the amount of excavated earth.