How cement “breathes in” and stores millions of tons of CO₂ a year
Researchers at MIT have produced the first detailed national estimate of how much carbon dioxide is naturally absorbed by cement in buildings and infrastructure over time. Their study shows that cement-based materials in the United States capture more than 6.5 million metric tons of CO₂ each year, offsetting about 13% of the emissions created during cement manufacturing. The same analysis found that Mexico’s building stock absorbs roughly 5 million tons annually, despite using less cement overall. This absorption happens as concrete and mortar slowly react with carbon dioxide in the air, turning it into stable limestone within the material.
To calculate these figures, the research team created representative “archetypes” of common structures and infrastructure rather than modeling every individual building. They found that carbon uptake varies widely depending on construction practices, material choices, structure design and climate. Mortar, for example, absorbs CO₂ much faster than dense concrete, which helps explain why Mexico captures a larger share of its cement-related emissions. The study suggests that design choices, such as increasing exposed surface area or avoiding overly strong concrete mixes, could safely enhance this natural uptake. Overall, the findings offer a more accurate picture of cement’s environmental impact and could improve how carbon absorption is reflected in national and international climate inventories.
