Quantifying concrete recarbonation potential: A life cycle approach to carbon uptake

Abstract

Concrete production is a major source of carbon emissions, but carbonation of concrete throughout its life is also a natural process that results in the sequestration of atmospheric CO₂ into the concrete. To understand the relationship between emission and sequestrations this study quantifies the carbonation potential of recycled concrete aggregate (RCA) across its full lifecycle, encompassing both service life and end-of-life, including stockpiling, recycling, and secondary use. An Empirical CO₂ Uptake Model for Concrete developed by IVL is used to predict carbonation depths in natural and the recycled concrete utilized as aggregate. This model assesses the carbonation uptake relative to both the CO2 generated from cement production and from concrete production in a standard bridge structure. The data shows limited carbonation occurs during the primary service life over 100 years, capturing only up to 2.99 % (5.85 kg CO2/m3) of calcination emission, while secondary applications add up to 2.66 % (5.19 kg CO2/m3). In contrast, the recycling and stockpiling phase achieves a higher rate of carbonation over a 12-month period, ranging from 31 to 65 % (61–128 kg CO₂/m3), depending on stockpile configuration and duration. Shallow, spread-out stockpiles maximize CO₂ absorption by increasing surface exposure and airflow. Dust particles fully carbonate within weeks (31 % of calcination emission), whereas larger particles carbonate progressively over time. Secondary use of RCA in new concrete further enhances its carbon sink potential due to its residual reactivity and increased porosity. Overall, concrete demonstrates substantial carbonation potential, with total CO₂ uptake ranging from 35 % to 68 % of calcination emission.</p