The construction industry, particularly concrete production, stands at a critical juncture in the global effort to combat climate change. As we seek innovative solutions to reduce greenhouse gas emissions, the non-combustive integration of biochar into concrete production has emerged as a promising avenue for decarbonizing this hard-to-abate sector.

The Concrete Challenge

Concrete, the ubiquitous foundation of modern construction, bears a significant environmental burden, accounting for 8% of global greenhouse gas (GHG) emissions. The production process of concrete, especially its key component cement, is inherently carbon-intensive; in fact, if the entire industry was ranked against the GHG emissions from countries around the world, it would be the third-largest emitter after only China and the United States.

To understand the scale of this challenge, we must delve into the composition of concrete. Typically, concrete consists of coarse aggregate (such as gravel or crushed stone), fine aggregate (like sand), water, cement (the binding agent), and various admixtures. The production of these components, particularly cement, contributes substantially to the industry's carbon footprint.

Key Drivers of Emissions 

Despite generally accounting for only 11% of concrete’s composition, cement production is responsible for 88% of the total CO2 emissions. Ordinary Portland cement (OPC), which is the type of cement most broadly used today, is made by combining limestone with silicate-containing materials in a kiln heated to 1,450°C. The high temperatures facilitate a chemical calcination process, in which the chemical bonds of the minerals break down, creating compounds called clinker and releasing CO2 as a by-product. The clinker is then ground into a fine powder and mixed with gypsum to create cement. 

Figure 1: Cement production GHG emissions in the U.S., 2021

Source: The Center for American Progress

Beyond the production of cement, an often-overlooked aspect of concrete's environmental impact is the use of aggregates. It is estimated that a staggering 17.5 billion tonnes of aggregates are utilized annually in concrete manufacturing. This massive consumption results in significant upstream emissions and environmental degradation due to the extraction, crushing, and transportation of these materials.

Current Mitigation Efforts

As a large amount of the overall process emissions occur during the chemical calcination step, primarily through the release of CO2 during the breakdown of limestone, the concrete industry is considered a hard-to-abate sector. This is because the process cannot be fully decarbonized by switching over to clean energy sources, requiring solutions that innovate the typical composition of cement without compromising performance and safety requirements. 

The concrete industry has not been idle in the face of these environmental challenges. Many companies have pivoted towards replacing 20-25% of cement with industrial byproducts like fly ash, silica fume, and waste glass. These materials, known as supplementary cementitious materials (SCMs), help reduce the overall carbon footprint of concrete production.

However, this approach is not without its limitations. These SCMs are often associated with carbon-intensive industries themselves and may face supply constraints in the future. As such, the search for more sustainable alternatives continues.

Biochar: A Promising Alternative

Enter biochar, a carbon-rich material produced from biomass through pyrolysis. This innovative material has emerged as one option for lower-carbon concrete. It offers two primary applications in concrete production:

1. As a filler in cement composites, reducing the amount of carbon-intensive clinker used
2. As a replacement for aggregates like sand in concrete mixtures

Evidence shows that once biochar is mixed into the concrete matrix, it will cure into a solid, durable material that enables long-term carbon storage. 

Benefits of Biochar in Concrete

The incorporation of biochar into concrete production offers several compelling advantages:

1. Compensating for Concrete’s GHG Emissions: Integrating biochar into concrete composites can reduce the amount of OPC content or fossil-based aggregates, lowering the overall GHG emissions from producing concrete. Moreover, research has indicated that biochar-based concrete can accelerate the rate of carbonation during cement curing, increasing the uptake of CO2 and lowering overall GHG emissions. 
   
   
2.  Enabling Carbon Removal: As a CDR technology, biochar has a negative carbon footprint, up to -3.3 kg of CO2-eq per kg of biochar, depending on location, feedstock, production methods, and end-use. To enable long-term CO2 sequestration, biochar requires usage in an application that preserves its carbon storage properties, such as concrete. Therefore, scaling the use of biochar-based concrete can drive increased opportunities for durable CDR storage. 
   
   
3. Improved Performance: While the structural impacts depend on the exact composition and production characteristics of the biochar-based concrete, adding biochar may enhance the strength, durability, and resistance of concrete products. Various studies demonstrated that plant-based biochar improved the compressive strength of OPC.
   
   
4.  Enhanced Thermal Properties: The porous nature of biochar facilitates effective heat absorption and storage. When used in construction applications in the built environment, such as walls and flooring, this can improve the insulation properties and contribute to more energy-efficient buildings.
5. Educational Awareness: There is growing interest and understanding among concrete and construction buyers about the potential of biochar in their industry.
   
   

Challenges and Considerations

Despite its promise, the integration of biochar into concrete production faces several challenges:

1. Pricing Considerations: Due to the high cost of biochar, concrete incorporating this material is likely to be positioned as a premium product with performance and sustainability benefits. The current combination of higher prices and low volumes makes it challenging for biochar-based concrete to integrate into commoditized concrete value chains. However, the additional carbon credit revenue streams can strengthen the business case for the biochar-based concrete. 
2. Regulatory Hurdles: Current structural concrete standards, particularly in the EU, do not have well-defined pathways to bring innovative building materials to market. This can limit early applications of biochar-based cement to non-load bearing applications, such as pavement and architectural elements. Some innovators are working to overcome these hurdles by obtaining the necessary certifications, such as the CE mark in the EU, although the approval process can be lengthy even if performance criteria is met. 
3. Variability in Biochar Properties: Not all types of biochar are suitable for concrete applications. The properties of biochar can vary significantly based on feedstock and production processes, affecting its suitability for concrete applications. This can also lead to consistency challenges for biochar-based concrete when the biochar is sourced from different productions facilities.“Cement substitution projects necessitate specific biochar products that achieve a balance among several factors: the chemical composition of the char, moisture levels for handling and controlled water addition in concrete, granulometry for integration into the mix, volume, carbon dioxide removal potential, and cost. This balance varies depending on the project and the concrete products being developed. Therefore, experience with biochar products and the biochar market is beneficial for successfully implementing such projects.” – Charles Peurois, CEO and Co-Founder of Enchar
4. Concrete Mix Sensitivity: Concrete mixes are sensitive to ingredient replacements. Biochar's porous nature can affect water absorption, potentially impacting the workability and curing time of concrete mixes. Additionally, biochar producers may be faced with additional processing requirements to not negatively impact the concrete mix:  “As a general rule, material in concrete must be in a stable form meaning that it cannot be further crushed by any stress on the material. This means that a particle size should be extremely small (we've heard <75 microns) so there is no air in the particle, which adds the requirement of milling it down from typical biochar particle size.” – Michael Douglas, Chief Revenue Officer of Onnu

Market Potential and Future Outlook

Figure 2: Historic and projected global cement production (million tonnes) by geography

 Source: Rhodium Group (2024)

As Figure 2 shows, the global demand for cement is not expected to decline any time soon, especially with current trends around urbanization and population growth. Thus, the potential for biochar in the concrete industry is substantial. 

In 2020, global concrete production reached 26 billion tonnes. If biochar was used to replace 10% of the cement for just 5% if the total market, it would require around 22 million tonnes of physical biochar annually. However, global biochar production in 2023 was only 350,000 tonnes. For biochar-concrete to be a viable market application and make a significant climate impact, the supply of biochar must scale rapidly. In fact, this is a major barrier to trials and large-scale demonstration projects today.

Case Studies and Industry Perspectives

Despite the barriers, there is growing interest in biochar-concrete applications with numerous Suppliers launching trials and demonstration projects to validate the use case. As one example, Pyrogen, a Puro.earth Supplier, is developing biochar-based cement to support affordable and sustainable housing in Kenya: 

"Pyrogen is proud to lead a pioneering pilot with CGAP, housed within the World Bank, and Habitat for Humanity to deploy our patented biochar concrete mix for affordable housing in Africa. This initiative merges sustainable construction with carbon finance through ‘green mortgages,’ leveraging carbon markets to reduce housing costs while driving climate impact and economic empowerment in Kenya." – Philip Maciocia, Co-Founder of Pyrogen

In Thailand, SCG Cement, in collaboration with its internal startup 'Arbon,' has begun implementing biochar concrete in various construction projects. This initiative aims to address PM2.5 pollution resulting from agricultural residue burning, generate income for farmers, and decarbonize the concrete and construction industries.

"Since last year, over 2,500 cubic meters of biochar-enhanced concrete have been produced and utilized in the construction and maintenance of pavements, successfully sequestering more than 100 tonnes of biochar. We anticipate increasing applications in the coming years to reinforce confidence in the performance of concrete structure with biochar. Our internal startup ‘Arbon’ has also developed a technology that allows biochar to improve strength of concrete, creating a critical step toward achieving net-zero goals This innovation not only reduces PM2.5 pollution but also generates an additional income stream for farmers, contributing to a more sustainable future." – Sakprayut Sinthupinyo, Green Circular Technology Director of SCG Cement and Co-founder of Arbon

The Path Forward

As we look to the future of sustainable construction, biochar-infused concrete offers a promising path forward. However, realizing its full potential will require concerted efforts from various stakeholders:

1. Investors: There's a need for increased investment in biochar production and research to scale up supply and improve understanding of its applications in concrete.
2. CORC Buyers: Purchasing Carbon Removal Certificates (CORCs) from biochar suppliers testing applications in cement can unlock significant co-benefits that support the decarbonization of this hard-to-abate industry.
3. Concrete and Construction Companies: Engaging with biochar suppliers to explore trials can help companies decarbonize their operations and position themselves at the forefront of sustainable construction practices.
4. Policymakers and Regulatory Bodies: Better defined pathways for innovative building materials can help expand the market for biochar-based concrete and enable structural applications. 
   
   

Conclusion

The integration of biochar into concrete production represents a promising pathway for decarbonizing the construction industry. While challenges remain, particularly in scaling production and achieving lower prices, as well as navigating regulatory hurdles, the potential benefits in terms of emissions reduction and improved concrete performance make this an exciting area for further research and development.

As we continue to seek innovative solutions to combat climate change, the use of biochar in concrete stands out as a compelling option that merits further exploration and investment. By bringing together stakeholders from across the value chain - from biochar producers to concrete manufacturers and construction companies - we can work towards a more sustainable future for one of the world's most essential industries.

The journey towards sustainable concrete is complex and multifaceted, but the integration of biochar offers a beacon of hope. As research progresses and production scales, we may soon see a future where our buildings and infrastructure not only serve their intended purposes but also actively contribute to carbon sequestration and environmental sustainability.

Acknowledgements 

Puro.earth would like to thank the following for their contribution to this article: Giorgio Ponte from ecoLocked; Charles Peurois from Enchar; Bryan Eagle from Glanris; Jason Mühleck from Holcim; Kathleen Draper from International Biochar Initiative; Giles Welch and Andrew Ingle from Onnu; Philip Maciocia from Pyrogen Energy; and Sakprayut Sinthupinyo from SCG Cement and Arbon. 

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