Building materials offer a significant opportunity for carbon dioxide removal (CDR), with the potential to store over 16 billion tonnes of CO2 annually. A study by Van Roijen et al. explored this potential, highlighting how relatively minor changes to material composition could lead to substantial carbon sequestration. This approach could be a crucial tool in achieving net-zero emissions, potentially offsetting roughly half of yearly global CO2 emissions.
The study found that fully replacing conventional building materials with CO2-storing alternatives in new infrastructure could sequester as much as 16.6 ± 2.8 billion tonnes of CO2 each year. This figure represents approximately 50% of anthropogenic CO2 emissions in 2021. The research emphasized that the total storage potential is more dependent on the volume of materials used than the amount of carbon stored per unit mass. This means that materials with lower carbon storage per kilogram but high usage, like concrete aggregates, still offer significant overall storage capacity. Furthermore, the carbon storage capacity of building materials will increase proportionally with demand, potentially reducing the need for more costly or environmentally risky geological, terrestrial, or ocean-based storage solutions.
The need for CDR stems from the challenge of achieving net-zero greenhouse gas emissions. This goal requires not only reducing emissions but also actively removing CO2 from the atmosphere. Building materials are particularly well-suited for this purpose due to two key characteristics: their vast quantity and their longevity. The cumulative mass of infrastructure materials produced globally is comparable to the combined mass of all human food, animal feed, and energy resources. Moreover, these materials remain in use for decades, ensuring long-term carbon sequestration. This combination of scale and durability makes building materials an ideal carbon sink. Unlike carbon capture and storage (CCS) which often requires new infrastructure like pipelines, utilizing existing material production offers a more readily available and scalable solution.
The production of conventional building materials is a significant source of greenhouse gas emissions, estimated at 3.5 to 11 billion tonnes of CO2 equivalent, representing 10 to 23% of global GHG emissions. Excluding energy-related emissions, process emissions from the building materials examined in the study accounted for approximately 1.8 billion tonnes of CO2 emissions in 2016, or about 5% of global CO2 emissions. The study investigated the potential of common building materials—concrete, brick, asphalt, plastic, and wood—to store carbon. Alloys were excluded due to their specific functional requirements and limited carbon storage capacity. The study calculated annual storage potential based on 2016 consumption levels, assuming all carbon within the materials originated from the atmosphere and that the storage is effectively permanent. The estimates focused on substituting conventional inputs with alternatives containing biogenic carbon (derived from recently photosynthesized atmospheric CO2) or key minerals (like recently formed carbonate minerals). The study assumed negligible use-phase emissions and minimal GHG emissions from landfilling at the end of life, although acknowledging that future research should consider these factors, such as emissions from demolition or the burning/decomposition of wood.
The research revealed that while bio-based plastics offer the highest storage potential per kilogram, their relatively low production volume limits their overall impact. Conversely, aggregates in concrete, despite having lower storage potential per kilogram, offer the greatest total potential due to their massive global demand. This highlights the importance of focusing on materials with high market penetration and scaling potential. Cumulatively, the examined materials have a storage capacity of up to 16.6 ± 2.8 billion tonnes of CO2. Concrete and asphalt aggregates account for the majority of this potential, at 11.5 ± 1 billion tonnes of CO2, due to their sheer volume of use. The study also explored different CO2 storage options in cement, finding that a magnesium oxide-based cement synthesized from forsterite and carbonated with 15 wt % biochar as filler offered the highest CO2 capture, with a total potential storage of 2.6 ± 1.1 billion tonnes of CO2. Bricks, with biomass fiber content, could store around 0.8 billion tonnes of CO2, equivalent to one-third of the brick mass. Mineral carbonation of calcium hydroxide in bricks could add another 1.2 billion tonnes. A 20% increase in wood consumption, supported by sustainable forestry, could lead to an additional 0.45 ± 0.09 billion tonnes of CO2 storage. Bio-based plastic and asphalt binder contribute a smaller amount, less than 5% of the total, due to lower consumption rates.
A sensitivity analysis confirmed that the mass of materials consumed is the primary driver of carbon storage, with concrete aggregate and cement having the highest impact. Resource availability was also assessed, focusing on industrial waste materials and end-of-life concrete as feedstocks for carbonate-based aggregates. This analysis suggested that roughly 2 billion tonnes of carbonate-based aggregate, storing 1 billion tonnes of CO2, could be produced from these resources. The study also found that substituting portions of bricks, asphalt, and cement with biomass-derived materials would require a manageable portion of annual agricultural residues, leaving a substantial amount available for other uses. The geographical distribution of material production and potential scale-up locations was also considered, highlighting regions with readily accessible mineral deposits and agricultural residues.
The study further evaluated the contribution of these technologies to CDR targets outlined by the Intergovernmental Panel on Climate Change (IPCC). Assuming constant material demand at 2016 levels (with a 20% increase for wood), a full transition to carbon-storing alternatives by 2025, 2050, or 2075 would result in 1380, 920, and 460 billion tonnes of CO2 stored by 2100, respectively. These figures exceed the CDR requirements for both 1.5°C and 2°C warming targets. Even with limitations on resource availability, implementing these technologies by 2045 and 2090 would still be sufficient to meet the median targets for 1.5°C and 2°C scenarios, respectively. However, the study acknowledges potential competition for these resources from other sectors and the need for sustainable practices and thorough accounting of GHG fluxes. The study also considered the impact of future material consumption changes, finding that a ±20% change in demand by 2100 could alter total annual storage from 13.2 to nearly 20 billion tonnes of CO2.
In conclusion, the study demonstrates the significant potential of building materials to act as a major carbon sink. By transitioning to carbon-storing alternatives, the built environment could play a crucial role in achieving global climate targets. While challenges remain in terms of cost, scalability, and performance validation, the findings highlight the importance of further research, development, and policy support for these technologies.
