Whole-life carbon emissions of concrete mixtures considering maximum CO2 sequestration via carbonation

Abstract

A comparison of cradle-to-gate embodied carbon emissions and carbon dioxide (CO2) sequestration potential due to carbonation of portland cement (PC), portland limestone cement (PLC), and limestone calcined clay cement (LC3) concrete mixtures is presented in this work. First, the cradle-to-gate embodied carbon emissions of the concrete mixtures were calculated using life cycle assessment (LCA). Then, the CO2 sequestration potential of each mixture was computed using a theoretical model for CO2 sequestration that was derived using principles of cement chemistry to account for the carbonation of both calcium hydroxide (CH) and calcium silicate hydrate (C-S-H). The results indicate that a theoretical maximum of 33 % of the cradle-to-gate embodied carbon emissions of the concrete mixtures analyzed herein can be realistically sequestered via carbonation. Data also substantiate that concrete mixtures with higher cradle-to-gate embodied carbon emissions sequester the most CO2. However, concrete mixtures with lower cradle-to-gate embodied carbon emissions, namely PLC and Type I, II, III, IV, and V mixtures with high-SCM replacements, typically yield the lowest whole-life carbon emissions. The results indicate that concrete mixtures with high SCM replacement should be prioritized—regardless of which cement is used to produce the concrete—from a whole-life carbon emissions perspective.