The climate benefits from cement carbonation are being overestimated

Rapid decarbonization of the cement industry is critical to meeting climate goals. Oversimplification of direct air capture benefits from hydrated cement carbonation has skewed the ability to derive decarbonization solutions. Here, we present both global cement carbonation magnitude and its dynamic effect on cumulative radiative forcing. From 1930–2015, models suggest approximately 13.8 billion metric tons (Gt) of CO₂ was re-absorbed globally. However, we show that the slow rate of carbonation leads to a climate effect that is approximately 60% smaller than these apparent benefits. Further, we show that on a per kilogram (kg) basis, demolition emissions from crushing concrete at end-of-life could roughly equal the magnitude of carbon-uptake during the demolition phase. We investigate the sensitivity of common decarbonization strategies, such as utilizing supplementary cementitious materials, on the carbonation process and highlight the importance of the timing of emissions release and uptake on influencing cumulative radiative forcing. Given the urgency of determining effective pathways for decarbonizing cement, this work provides a reference for overcoming some flawed interpretations of the benefits of carbonation.

Elisabeth Van Roijen, Kati Sethares, Alissa Kendall, Sabbie A. Miller