Only two years ago, researchers from Heriot-Watt University in Scotland, led by Dr. Mehreen Gul, were investigating the use of biochar as an innovative, low-carbon building material.
Gul spoke of the great promise of using biochar in concrete mixes.
“Replacing as little as one per cent of a fine aggregate with biochar in cement can improve compressive strength by around 10 per cent.”
Biochar is produced by heating organic biomass from food, sewage, paper, agricultural and forestry waste in the presence of little or no oxygen. Biochar locks in carbon from these organic materials, avoiding their decomposition and the release of carbon dioxide into the atmosphere. In this way, it can help buildings act as “carbon sinks.”
In fact, it is estimated each kilogram of biochar prevents the release of up to three kilograms of CO2.
At the time, Gul hoped her team’s research into the various advantages of biochar would lead to quicker adoption by the industry as a whole.
“Crucially, we’ll be consulting with key industry players to understand the effectiveness, readiness, cost, social acceptability and any limitations of biochar as a building material.”
Acceptance has already begun. Swiss-based Holcim, one of the world’s largest producers of concrete mixes using plants, began including biochar in a number of pilot projects in Europe in 2025, says Edelio Bermejo, the company’s head of Global R&D.
Holcim partnered with Pritzker Prize-winning architect Alejandro Aravena of design firm ELEMENTAL on a new biochar technology. A scalable prototype was presented in Venice during the 2025 Architecture Biennale.
Holcim then followed up in 2025, using biochar created from forestry residues and coffee grounds in test pours in collaboration with London’s Canary Wharf Group, resulting in the development of their first net-zero concrete.
“The aim of these trials was to show that next-generation concrete mixes can perform as well as, or better than, standard concretes – giving contractors and the wider supply chain confidence to adopt them and embedding circular thinking into the buildings we help create,” said Jasen Gauld, national Readymix product development director for Holcim UK.
“Mainstream applications of biochar are becoming more widespread,” said Bermejo. “Our customers no longer view biochar as a niche experimental additive, but as a high-performance material to reduce emissions.”
Beyond biochar, Bermejo says calcined clay will also become be a key ingredient in more of Holcim’s cement formulations in 2026.
“This supplementary cementitious material (SCM) can halve the CO2 footprint of cement with no compromise on performance, and it reduces dependence on traditional low-emission SCMs such as slag and fly ash, industrial byproducts that are becoming increasingly scarce or expensive.”
As part of Holcim’s global strategy to increase sustainability across its production, the company has also targeted a 33 per cent reduction in its overall freshwater intake by 2030. The company has been piloting an initiative in Ecuador and Mexico by integrating its operations with the water cycles of nearby industries.
This “radical rethinking of our supply chain,” is based on the understanding that “one industry’s ‘wastewater’ is a vital resource for another.”
In another avenue of study, researchers from the Norwegian University of Science and Technology (NTNU) and the University of Tokyo have investigated using plentiful desert sand to create a new mix they call Botanical Sand Concrete or Sandcrete. Sand for concrete currently sourced from riverbeds and banks, the ocean floor and rocks crushed from underground pits can have major environmental impacts when carried out on a large scale.
The Sandcrete blend is formed when desert sand is pressed together with tiny pieces of wood under with varying amounts of heat. The lignin in the wood acts as a natural binder rather than relying on cement hydration.
Using desert sand is not an entirely new idea. However, it has never been considered appropriate for traditional concrete mixes because it is too fine-grained, resulting in a concrete that is not hard enough for construction purposes.
Ren Wei, a researcher at NTNU’s Department of Manufacturing and Civil Engineering, explained experiments have been carried out in the laboratory at the University of Tokyo to determine how various factors affect the strength and density of the materials, including temperature, mixing ratio, pressure, pressing time, and different types of sand.
The tests have produced a concrete strong enough to make paving stones for pavements and walkways. It is hoped that further investigation will increase Sandcrete’s range of use, such as indoor applications. However, further testing and experimentation will be required to determine how well Sandcrete can withstand cold temperatures.
Another factor is the matter of transportation. Shipping desert sand long distances to concrete manufacturing facilities could negate much of the material’s environmental benefits.
The concept holds great promise nevertheless since deserts cover an estimated 19 million square miles of the earth.
As NTNU expresses it, “With further development, botanical sand concrete could become part of the sustainable building materials of the future and perhaps solve a global paradox: that we crush mountains while drowning in sand.”
John Bleasby is a freelance writer. Send comments and Climate and Construction column ideas to [email protected].
