Researchers from Aalto University and VTT Technical Research Centre of Finland have successfully developed a bio-based binder material that offers a carbon-negative alternative to traditional cement. This development could transform construction by reducing emissions and even turning certain infrastructure projects into carbon sinks.

The Problem with Cement
Cement is widely used as a binder in construction to stabilise soil at building sites, but it is also the third-largest carbon emitter globally, following the energy and fossil fuel industries. As the industry faces growing pressure to reduce its environmental impact, finding sustainable alternatives to cement has become crucial.

Introducing Biochar as a Sustainable Binder
The new binder material developed by Finnish researchers is biochar—a carbon-rich by-product of the biofuel industry. Its use as a binder for ground improvement could cut emissions from the manufacturing process by up to 75%, without compromising the strength or durability of infrastructure. Biochar is produced by heating organic waste at high temperatures in an oxygen-limited environment, capturing carbon in a solid form that can be put to various beneficial uses.

Carbon-Negative Infrastructure
The researchers were also able to make infrastructure itself carbon-negative by binding CO₂ in a stable form within the material’s clay layer. According to Sanandam Bordoloi, Assistant Professor of Geotechnical Engineering at Aalto University, “Biochar’s use in place of cement can reduce emissions significantly while maintaining the durability of structures. Our latest tests show that carbon dioxide can be bound within the cementitious clay layer, opening opportunities for next-generation building materials that sequester carbon.”

Potential Applications
This approach could have a significant impact, especially for infrastructure projects like roads, bridges, and tunnels. These projects frequently rely on cement to stabilise clay soils, which is common in various regions worldwide, from the Nordics to parts of Asia and South America. Instead of contributing to the carbon footprint, such infrastructure could, in theory, act as a carbon store.

A Paradigm Shift in Ground Improvement
Professor Leena Korkiala-Tanttu, Senior Adviser at Aalto, explained, “Until now, no one had succeeded in binding carbon dioxide effectively in weak clay that is problematic for construction. Our research could be a paradigm shift in reducing the need for cement—particularly in ground improvement—as we can now turn our attention to biochar and other recycled industrial by-products that offer good performance both in terms of strength and emissions reduction.”

Future Developments and Field Testing
The team is now preparing to test the technology in the field and is exploring other applications in construction, such as using recycled waste material in non-structural backfill or noise barriers. Their innovation also involves the use of waste materials as raw input for various parts of construction, further promoting a circular economy.

Sustainable Properties of Biochar
Biochar has numerous sustainable properties that make it attractive beyond construction. It is carbon-negative, meaning it captures and holds more carbon than is released during its production. Additionally, biochar can be used to improve soil health by aerating soil, reducing acidity, and helping to sequester nutrients, offering potential applications in landscape architecture as well.

Challenges in Adoption
The construction industry is often conservative, which can make the adoption of new materials slow, particularly as buildings and infrastructure are typically expected to last for over a century. However, as sustainability becomes an increasingly urgent goal, innovations like carbon-negative biochar could pave the way for greener construction solutions and set new standards for sustainability in design disciplines.

Source: Aalto University
Photos: Aalto University