Writing in the journal Sustainability, scientists from Colorado State University’s System Engineering Department have investigated a novel route toward achieving carbon-neutral building. The research has focused on the effects of the interaction between biochar and CaCO3 in sustainable concrete with carbon capture capabilities.
Study: Toward Carbon-Neutral Concrete through Biochar–Cement–Calcium Carbonate Composites: A Critical Review. Image Credit: Isarapic/Shutterstock.com
Carbon Storage Using Green Hybrid Concretes
It has become apparent in recent years that reducing emissions alone will not adequately address the challenges of anthropogenic climate change. Whilst it is a key strategy for limiting global temperature rises to 1.5oC, other technological solutions are needed to increase the chances of mitigating the effects of growing carbon emissions and industrial activity.
Key amongst technological solutions proposed to overcome the issues of rising global temperatures and environmental damage, carbon capture storage shows vast potential. It has been estimated that cumulative uptake of between two hundred and four hundred gigatonnes of carbon dioxide before the end of this century will be needed to mitigate the worst effects of climate change. Additionally, reducing the land needed for carbon storage is an important consideration for researchers.
Whilst there are numerous carbon capture and storage technologies being researched and developed, using concrete to store carbon offers an intriguing and future-ready solution to the issue. Constructing buildings out of this material provides a permanent and high-density form of carbon capture and storage.
Calcium Carbonate and Biochar
In research into these hybrid green concretes, two materials have been investigated to manufacture composites: CaCO3 and biochar. Both materials offer high-density carbon storage possibilities. Biochar is produced from a wide range of agricultural and food waste biomass using pyrolysis methods. Depending on the feedstock, the energy required for its production varies.
Currently, the main use of biochar is in the agriculture industry for amending soils. Whilst this is a key commercial activity, only a certain amount of biochar can be used for this purpose, with application rates typically exceeding no more than twenty tons per hectare. Furthermore, if biochar has a high oxygen-carbon ratio, the half-life of the material is severely reduced.
CaCO3 is also used in the agricultural industry. Also called agricultural lime, it can permanently store carbon (its performance can be affected by acidic soils or calcination temperature), but its carbon content is less than biochar by weight. Like biochar, there are limits to how much of this compound can be used in soil. Both materials have been explored in-depth as additives and amendments in cement and concrete.
The paper has provided a review of current literature, examining the benefits of using both carbon materials in the production of these hybrid concretes. Furthermore, the authors have identified and elucidated new research opportunities that will help to identify the optimal amounts of these additives and amendments for cement.
Methods for producing this composite concrete have been discussed in-depth in the review. Performance expectations have been highlighted, including compressive strength, carbon storage, and other mechanical properties. Moreover, the obstacles to industrial-scale applications have been highlighted, such as codes and standards, cost, and the availability of materials. Finally, six research directions that can guide future improvements are discussed by the authors.
Research directions explored are the continued exploration of composite material properties, modeling important material properties and interactions, examining the long-term durability of biochar-containing concretes, looking at the enhanced use of life-cycle assessments, enhancing carbon negativity by functionalizing biochar with CO2 absorbance capabilities, and overcoming the social and economic barriers to industrial-scale production and use.
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Both materials have been evaluated separately in cementitious composites, displaying improved compressive strength. Based on these results, the authors have concluded that using both materials will be advantageous. In terms of carbon capture and storage, the authors have stated that a concrete-based system could store all carbon necessary to mitigate temperature rises this century.
It could also help reduce cement usage by replacing conventional materials. Clinker needs would be reduced during production, further reducing CO2 emissions. Taken together, it can be seen that using CaCO3 and biochar as materials for this type of hybrid concrete can improve the environmental friendliness of new construction projects. Waste streams can be valorized, both from the construction industry and from industries such as agriculture or forestry.
The authors have noted that whilst research indicates that biochar-calcium carbonate-cement composites may possess sufficient compressive strength, in situations where they do not meet these requirements, they can still be used in non-structural construction elements, which can be of environmental and social benefit. More research on these composite, hybrid concretes is needed to fully realize their potential.
Winters, D. Boakye, K. & Simske, S. (2022) Toward Carbon-Neutral Concrete through Biochar–Cement–Calcium Carbonate Composites: A Critical Review [online] Sustainability 14(8) 4633 | mdpi.com. Available at:
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