High-density, high-permanence forms of carbon storage are in demand to save storage space on land or at sea while allowing the world to reach its climate targets. Biochar and calcium carbonate are two such forms that have been considered largely separately in the literature for carbon storage. In this paper, we consider how biochar and calcium carbonate might interact when they are used together with cement as part of a carbon storage system, ideally to form a carbon-neutral concrete. The carbon storage system stores atmospherically absorbed CO₂ within concrete, thereby reducing carbon in the atmosphere. In addition, such a system will help in reducing cement usage, thus reducing the need for clinker in cement manufacturing and directly reducing CO₂ emissions that result from limestone calcination during clinker manufacturing. Another benefit of such a composite storage system is its use in building structures, a use that has positive environmental and social impact. Thus, further research on the properties of this composite material is warranted. This paper explores the literature on the use of biochar combined with calcium carbonate and cement as carbon storage material. The use of recycled carbon aggregates (RCAs) and LC3 concrete as part of this approach is reviewed. The paper also addresses the possible compressive strength range of the biochar–cement–calcium carbonate composite material, along with other performance expectations. Obstacles to scaling the use of carbon-neutral concrete are identified and an array of research directions are presented, with the goal of improving carbon-neutral concrete and its use.

The cement and concrete industries face significant challenges in decarbonization due to escalating demand driven by rapid urbanization, population growth, and infrastructure restoration needs. Cement production alone accounts for 8% of global anthropogenic CO₂ emissions, underscoring the urgency of exploring pathways to achieve net-zero emissions in these sectors. With over 120 nations committing to net-zero targets by 2050, a comprehensive examination of emerging carbon-saving technologies is imperative. While several promising innovations are in nascent stages, rigorous life cycle assessments are essential to determine their potential for carbon reduction. Practical strategies for achieving net-zero objectives and UN sustainability goals involve embracing circular economy principles, harnessing diverse by-product sources, fostering stakeholder engagement, and fostering technological innovation. An efficiency approach that integrates advancements in materials science, alternative fuels, and sector-wide efficiencies is crucial for success. This assessment identifies promising technologies, highlights knowledge gaps, underscores the importance of further research, and offers recommendations for implementing best practices on the path to net zero.