Houses, roads, industrial parks – all are still traditionally built with concrete. Though, the steadily increasing demand is accompanied by an increasing scarcity of resources. At the same time the greenhouse gas emissions of the concrete industry accounts for more than 11 percent of global emissions. Due to the problematic Life Cycle Assessment of concrete, improvement and alternatives are needed. The good news is – the construction industry can make a major contribution to climate protection through carbon storage.
Benefits of Concrete with Biochar
- Improved mechanical properties such as compressive strength and fire resistance12014, Hans-Peter schmidt “The use of Biochar as Building material – Cities as Carbon Sinks”, The Biochar Journal
- Reduced carbon footprint of buildings and road infrastructure
- When incorporated into roads: pollutant retention, adsorption of de-icing salts and petroleum residues, filtration of rainwater
Biochar is an efficient binder used in concrete. In certain mixes, the targeted addition can improve flexural strength and fire resistance. Biochar improves the rheology of concrete. In buildings, biochar provides chemical stability, water holding capacity and crack resistance of concrete2Shailey Singhal (2022) Biochar as a cost-effective and eco-friendly substitute for binder in concrete: a review, European Journal of Environmental and Civil Engineering, DOI: 10.1080/19648189.2022.2068658.
In roofs and other lightweight construction applications, the weight of concrete is reduced by the biochar. Silicate aggregates in concrete can basically be replaced by biochar. Biochar concrete also filters surface run-off or infiltrating rainwater and adsorbs salts and petroleum residues washed off the road. Low-quality biochar can also be used for all of the above applications.
The biochar is stored in the concrete removing carbon from the atmosphere for centuries. Concrete is thus no longer a climate killer, but has the potential to become a carbon sink. Concrete containing plant carbon (Charcrete) can be used in all construction projects to improve their Life Cycle Assessment. Concrete not only can become carbon neutral in its carbon footprint, but even climate positive, and with improved material properties as well. This is possible by replacing the scarce and conflictual amendments sand and gravel for concrete with locally produced biochar. Just adding one percent by mass of biochar to concrete could sequester about 20% of the annual CO2 emissions caused by the cement industry3Banjo A. Akinyemi, Adeyemi Adesina, Recent advancements in the use of biochar for cementitious applications: A review, Journal of Building Engineering, Volume 32, 2020, 101705, ISSN 2352-7102, https://doi.org/10.1016/j.jobe.2020.101705..
State of the Development for Concrete
Within the last few years, some products have reached market readiness. Concrete containing biochar is already available in the form of precast concrete elements and concrete paving blocks. Currently, various formulations of concrete containing biochar are being developed in a number of public and private research projects. For example, research is being conducted on the use of biochar in combination with calcium carbonate (CaCO3) in concrete, to create carbon storage systems based on carbon neutral concrete4Winters D, Boakye K, Simske S. Toward Carbon-Neutral Concrete through Biochar–Cement–Calcium Carbonate Composites: A Critical Review. Sustainability. 2022; 14(8):4633. https://doi.org/10.3390/su14084633.
Application
For the production of concrete containing biochar, an addition of 1-3% biochar is considered optimal.5Shailey Singhal (2022) Biochar as a cost-effective and eco-friendly substitute for binder in concrete: a review, European Journal of Environmental and Civil Engineering, DOI: 10.1080/19648189.2022.2068658. Other suppliers add more than 10% fine-grained biochar to concrete.
For targeted use, the biochar must be carefully selected, as each biochar is different due to the source materials as well as the way it is produced.
The process of bonding with concrete is irreversible, meaning that it cannot be reversed. The biochar will therefore always remain in contact with the concrete, even in each recycling cycle. No degradation rate has to be assumed for the biochar when it is used in concrete – it therefore remains 100 percent stored for the long term.
Certification
Biochar intended for usage in a concrete product can be certified according to the European Biochar Certificate (EBC) in the lowest quality class EBC-BasicMaterial, which also complies with the requirements of the EU REACH Regulation6REACH COMMISSION REGULATION (EU) No 1272/2013 of 6 December 2013 amending Annex XVII to Regulation (EC) No 1907/2006 of the European Parliament and of the Council on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) as regards pol. EU-Regulation 2013, 1272/2013. This ensures basic requirements for the biochar7EBC (2012-2022) ‘European Biochar Certificate – Richtlinien für die Zertifizierung von
Pflanzenkohle’, Ithaka Institute, Arbaz, Switzerland. http://www.european-biochar.org
Version 10.1G vom 10. Januar 2022.
Since 2022, it has been possible in Germany to have a concrete product with a reduced carbon footprint certified according to the Concrete Sustainability Council (CSC) certification for the cement, raw materials, and concrete industry8Concrete Sustanablity Council https://www.csc-zertifizierung.de/.
In concrete, there is little possibility of heavy metals being leached out. For this reason, EBC-BasicMaterial only requires the declaration of heavy metal contents, but does not specify threshold values. Organic pollutants must in part be analytically verified in compliance with specific threshold values. The standard also provides that EBC-BasicMaterial may only be “traded to other companies (B2B) “that fulfil certain handling requirements.
If an concrete additive is to be used outside the European requirements, since September 2023 the World Biochar Certificate (WBC) can be acquired using the WBC material class to guarantee sustainable production.
Another class is EBC-ConsumerMaterials, which, like EBC-BasicMaterial, is intended for non-soil applications, but has a stricter PAH threshold value for use in contact with living organisms and ecosystems9PAH = Polycyclic aromatic hydrocarbons. A third class is EBC-Urban, which is used for the application of biochar in e.g. urban greenery and rainwater filtration and is intended to prevent groundwater and surface water from becoming contaminated. In contrast to EBC-BasicMaterial, EBC-ConsumerMaterial has a stricter threshold value for EFSA PAHs (1 g/t dry matter) and the declaration of a further 16 organic pollutants in accordance with EPA specifications10European Food Safety Aithority, EFSA opinion on suitable indicators for both the occurrence and toxicity of polycyclic aromatic hydrocarbons (PAHs) in food, 4 August 2008https://www.efsa.europa.eu/en/news/efsa-opinion-suitable-indicators-both-occurrence-and-toxicity-polycyclic.
These differences result from the “acceptability of biochar for a specific purpose in relation to applicable laws, regulations and relevant industry standards” regardless of its quality. Further classes are to be introduced in 2022, aligned with demand, e.g. specific to building materials.11EBC (2012-2022) ‘European Biochar Certificate – Guidelines for a Sustainable Production of Biochar.’ European
Biochar Foundation (EBC), Arbaz, Switzerland. (http://european-biochar.org). Version 10.1 from 10th Jan 2022
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