Concrete's CO₂ absorption too slow to offset production emissions, study finds

Cement production, a key component of concrete, accounts for approximately 10% of global carbon dioxide emissions, primarily due to the high temperatures required to heat limestone. While concrete does absorb small amounts of CO₂ from the atmosphere over its lifespan, a UCLA-led study published in Communications Sustainability indicates this passive process, known as ambient carbonation, is insufficient to offset production emissions.

Researchers utilized thermodynamic and diffusion modeling to assess the rate and extent of CO₂ absorption in concrete structures. The study found that ambient carbonation offsets less than 10% of the cement industry's annual emissions, a figure significantly lower than previous estimates that suggested up to 57%. Under typical outdoor conditions, a concrete element would require about 1,000 years to reach 50% carbonation.

While demolition and crushing can accelerate carbonation, the study notes that the common practices of landfilling, stockpiling, or using crushed concrete in low-exposure applications like road bases limit further CO₂ uptake. Lead researcher Gaurav Sant emphasized that ambient carbonation "cannot be relied upon as a meaningful tool for reducing atmospheric carbon dioxide accumulations" and is too slow to meet the industry's 2030 goal of a 40% emission reduction.

The study suggests that the industry should prioritize active technological solutions for emission reduction at the point of production. These include minimizing cement usage, substituting with lower-carbon materials, employing alternative fuels, implementing carbon capture technologies, and developing novel cement production methods. The findings are crucial for accurate national climate inventory reporting, preventing overemphasis on long-term abatement processes with marginal benefits.