Sequester CO2 with biochar-enhanced concrete

The world is adding the equivalent of the city of Madrid every week to meet the needs of an urbanizing world and the desire for better living standards. This is driving demand for innovative and sustainable building solutions. These global megatrends are driving demand for innovative and sustainable building solutions. As the leading partner for sustainable construction, Holcim is pioneering innovation in the sector to bring game-changing solutions tailored to customers’ and society’s needs, and to decarbonize the built environment at scale.

Holcim partnered with Pritzker Prize-winning architect Alejandro Aravena and his firm ELEMENTAL to present a new biochar technology that transforms buildings into carbon sinks, which were presented during the 2025 Venice Biennale

At the end of life, organic matter releases CO2 into the atmosphere. By converting it into a charcoal-like material called biochar through pyrolysis, carbon that would have been released as CO2 is permanently sequestered. Acting in this way as a carbon sink, biochar can be added to low-carbon formulations of building materials including cement, mortar and concrete to further reduce their CO2 footprint, with no compromise in performance. One kilogram of biochar prevents the release of up to 3kg of CO2. In addition, biochar contributes to the circular economy by recycling organic materials. More on the process here: https://www.holcim.com/who-we-are/our-stories/the-power-of-biochar

Holcim and ELEMENTAL used this carbon sink technology for the first time in a full-scale Basic Services Unit housing prototype, presented in Venice during the 2025 Architecture Biennale. For this prototype, Holcim specially created a net-zero* biochar concrete that also incorporates circularity, with 100% recycled aggregates inside. (*scope of concrete production phases [A1-A3 cradle to gate] in Life Cycle Assessment. Assumes average transportation distance of 300km for cement and filler & 100km for aggregates.)

In the UK, Holcim created an innovative biochar concrete mix using recycled coffee grounds to support a 12-meter high sculpture of a blue whale in London’s Canary Wharf. The Whale on the Wharf (Skyscraper) by StudioKCA was created from plastic waste recovered from the Atlantic and Pacific oceans and has been sited in a wet dock in Canary Wharf’s Wood Wharf district. But the four-storey high structure required firm counter-weight foundations to keep it and its frame in place. Canary Wharf Group (CWG) turned to Holcim UK to develop an innovative concrete to support it and the circular economy message the sculpture embodies. Holcim experts devised a concrete mix containing biochar sourced from coppiced UK fast growing hard woods and spent coffee grounds from Canary Wharf’s cafes and restaurants to form the structural supports to anchor the sculpture in place. The mix produced to support the whale sculpture was formulated with carbon-reducing limestone fines and Ground Granulated Blast-furnace Slag (GGBS). With the addition of the 'Bio-Espresso' biochar, the embodied carbon was able to be lowered by a further 66%, yielding an impressive next-generation concrete with a projected net Global Warming Potential or GWP (A1-A3), as low as 69 kg CO₂e/m³. With the two technologies combined, the total carbon reduction is about 79% compared to a traditional CEM I concrete mix.

For the start of The Ocean Race Europe 2025, Holcim created Net-Zero* Xstone—a pioneering coastal protection block that combines biochar and bio-active concrete to tackle both climate change and biodiversity loss. Holcim donated it along with a 3D-printed bioactive reef to the city of Kiel where The Ocean Race Europe began. Xstone is a coastal armor block that not only protects against waves, but also functions as a natural reef while saving material through its smart, sustainable design using bio-active and low-carbon concrete. By integrating biochar, Holcim made several of the Xstones that comprise the reef net-zero* over their life cycle. Holcim used ECOPlanet low-carbon cement and recycled aggregates in production. A LCA confirms the product's carbon neutrality in its production stage (A1-A3). Xstone is a milestone in sustainable marine engineering—combining coastal resilience, carbon removal, and ecological regeneration in one modular solution.

Sustainability impact

Climate

According to the Intergovernmental Panel on Climate Change, biochar has the global potential to eliminate 2.6 billion tons of CO2 per year, across all industrial applications. That is the equivalent of taking 565 million passenger cars off the road for a full year.

In construction, biochar can be added to low-carbon formulations of building materials including cement, mortar and concrete to further reduce their CO2 footprint, with no compromise in performance. One kilogram of biochar prevents the release of up to 3kg of CO2.

Nature

At the end of life, organic matter releases CO2 into the atmosphere. By converting it into a charcoal-like material called biochar through pyrolysis, carbon that would have been released as CO2 is permanently sequestered. Biochar contributes to the circular economy by recycling organic materials.

Social

Approximately 1.6 billion people worldwide lack access to adequate housing and infrastructure. Concrete is the only building solution that can address the scale and scope of these global challenges. These global megatrends are driving demand for innovative and sustainable building solutions. Driven by a vision to be the leading partner for sustainable construction, Holcim is pioneering innovation and decarbonization in to bring game-changing solutions tailored to customers’ and society’s needs.

Holcim and ELEMENTAL used this carbon sink technology for the first time in a full-scale Basic Services Unit housing prototype, presented in Venice during the 2025 Architecture Biennale. The project follows the principle of incremental design, which entails fast and efficient construction through the provision of essential housing components, while empowering people to finish building their homes themselves. Such a model has been built more than 4,000 times in Latin America over the past 20 years. Holcim’s new decarbonization technology helps address the scale and speed of the housing crisis' demand without putting a strain on the environment.

Business impact

Benefits

The expertise in product mix design provided by Holcim allows for the integration of the biochar technology into concrete without compromising the material’s structural performance or long-term durability. Biochar building products are custom formulated to leverage diverse local biomass waste feedstocks, ensuring consistent quality across different geographies.

This approach provides a seamless pathway for adoption as it requires no changes to existing construction practices or habits. Builders can use the material as they would use conventional concrete (construction crews will not require any specific training to work with this new material) and design possibilities do not require re-engineering. Construction schedules will not be affected. This compatibility is a significant advantage for rapid and widespread implementation of the solution across the building industry.

Costs

Biochar technology stands out among engineered Carbon Dioxide Removal (CDR) technologies for its high technological readiness and competitive cost-effectiveness.

Its TRL (Technology Readiness Level) is positioned up to 9 (system proven in an operational environment), which is higher than many other engineered CDR solutions like Direct Air Capture and Storage (DACS) of Enhanced Weathering (EW) which are often in the medium TRL range (4-6).

Biochar sits at the lower end of the price spectrum, making it highly attractive for scaling up near-term removal effort (on average $179/t CO2 for Biochar compared to an average price of $388/t across all CDR approaches (Word Economic Forum data).

Despite the cost competitiveness of biochar as a CDR, biochar concrete currently faces substantial added costs due to the inclusion of this new component. These costs are expected to fall as biochar production industrializes. Importantly, biochar pyrolysis also generates renewable energy (heat, electricity), which can be utilized in innovative business models to accelerate the technology’s adoption.

Impact beyond sustainability and business

Co-benefits

With this groundbreaking technology, construction products and solutions such as cement, mortar and concrete can be a powerful tool in the architect’s toolbox to build the affordable and resilient housing millions of people around the world need without putting further strain on the environment. Biochar’s use in the construction industry holds significant promise. Holcim is carrying out pilot projects in different countries, to help its customers meet their sustainability ambitions, with no compromise in performance.

Field data from these pilot projects will be used to document performance advantages brought by the biochar addition, like superior durability, which are already well established in scientific literature. The biochar physical properties offer many avenues to further enhance concrete performance. As an example, benefits such as pollutant adsorption can be leveraged in synergies with already commercialized water-permeable concrete solutions.

Typical business profile

Leading sustainability actors in the construction value chain, from architects to urban planners and developers to contractors.

Approach

1. Project-specific evaluation and objective setting

   1. embodied carbon footprint - quantify the target reduction in embodied carbon;

   2. circularity - assess the potential of using locally sourced or waste-derived materials (including biochar from sustainable sources and recycled aggregates) to enhance the project’s circular economy metrics;

   3. performance requirements - clearly define the required structural performance, durability, workability and aesthetic considerations for the concrete application.

2. Formulation development and net-zero strategy:

   1. optimize biochar inclusion - starting with an already low carbon formulation, determine the optimal dosage for maximum carbon sequestration potential, while maintaining required strength and durability;

   2. maximize recycled content - incorporate other sustainable components to further reduce the use of virgin materials;

   3. initial lab testing - conduct small-scale laboratory tests on formulations.

3. Technical documentation and sustainability verification

   1. the technical data for design - compile a comprehensive technical data sheet for the biochar concrete formulation;

   2. Life Cycle Assessment (LCA) documentation.

4. Optional mock-up trial and contractor testing: test the product’s workability, pumpability and finishing in order to proceed to practical adjustments before full-scale use.

5. Full-scale implementation and post-construction review

   1. implement the verified mix design with rigorous quality control and on-site monitoring;

   2. document the actual reduction in embodied carbon against the initial target and gather feedback from contractor, consultant and owner to refine the process for future projects.

Stakeholders involved

Implementation of a novel solution such as biochar concrete requires collaboration of all actors in the value chain, starting as early as possible in the project definition: real-estate developer, owner, architect, material supplier, engineering consultant, contractor, sub-contractor.

Key parameters to consider

Integrating biochar into a concrete mix design presents an initial challenge, as its porous nature, high surface area and potential variable composition can significantly influence the fresh (workability, setting time) and hardened (strength, durability) properties of the concrete. This effect must be carefully managed to prevent jeopardizing the overall product performance, meaning the concrete must meet required standards for strength, longevity, and safety. This complexity is amplified by the simultaneous use of 100% recycled aggregates.

The combination of these two components necessitates deep expertise in concrete formulation.

A rigorous Life Cycle Assessment (LCA) is absolutely necessary to accurately demonstrate the overall reduction in Global Warming Potential (GWP). This involves, for example, quantifying sequestration, and assessing environmental burdens associated with all manufacturing steps.

In essence, the initiative requires a scientific, holistic and expert-driven approach to engineering a high-performance low carbon building material.

Then, the successful market introduction of biochar-enhanced concrete hinges on two key factors: its ease of use for contractors and its environmental benefits in forward-thinking markets.

Contractors can manage, pour, finish and cure the innovative concrete using their existing equipment, skills and site practices. This parity with traditional concrete is very important because the construction industry is notoriously conservative and risk-adverse regarding new materials.

The environmental benefit of this concrete – specifically its potential for lower embodied carbon due to carbon sequestration from biochar and the use of recycled aggregates positions it perfectly for markets with progressive building regulations markets with already existing building regulations on embodied carbon or those offering incentives for low-carbon construction are highly favorable for the initiative’s implementation. These regulations create a market pull, where developers and builders are legally required or financially motivated to select materials that demonstrably lower their project’s Global Warming Potential (GWP).

Implementation and operations tips

A strong collaboration among all key stakeholders (the owner, designer, material supplier and contractor) is necessary to succeed. Common vision and teamwork will ensure the innovative solution moves effectively from concept to completion and will drive larger-scale adoption. It requires defined roles in the collaborative framework:

• The owner/developer should provide the strategic mandate and funding: setting the overarching sustainability goals and providing the budget and schedule allowances

• The designer/engineer should ensure technical integration and validation: specifying the biochar-enhanced concrete within the design and performing performance verification

• The material supplier should provide expertise and quality in supply: providing rigorous technical data and offering on-site support to address any material-specific concerns

• The contractor/builder should ensure constructability and execution: providing feedback on material's handling and ensuring the theoretical concept is practically implemented on site