新しい添加剤により、コンクリートを効果的な炭素吸収源に変身させることができる(New additives could turn concrete into an effective carbon sink)

2023-03-28 マサチューセッツ工科大学(MIT)

＜関連情報＞

• https://news.mit.edu/2023/new-additives-concrete-effective-carbon-sink-0328
• https://academic.oup.com/pnasnexus/article/2/3/pgad052/7089570?login=false

CO2をC-S-Hに固める：コンクリートカーボンニュートラルへの一歩 Cementing CO2 into C-S-H: A step toward concrete carbon neutrality

Damian Stefaniuk, Marcin Hajduczek, James C Weaver, Franz J Ulm, Admir Masic
PNAS Nexus  Published:28 March 2023
DOI:https://doi.org/10.1093/pnasnexus/pgad052

Abstract

Addressing the existing gap between currently available mitigation strategies for greenhouse gas emissions associated with ordinary Portland cement production and the 2050 carbon neutrality goal represents a significant challenge. In order to bridge this gap, one potential option is the direct gaseous sequestration and storage of anthropogenic CO₂ in concrete through forced carbonate mineralization in both the cementing minerals and their aggregates. To better clarify the potential strategic benefits of these processes, here, we apply an integrated correlative time- and space-resolved Raman microscopy and indentation approach to investigate the underlying mechanisms and chemomechanics of cement carbonation over time scales ranging from the first few hours to several days using bicarbonate-substituted alite as a model system. In these reactions, the carbonation of transient disordered calcium hydroxide particles at the hydration site leads to the formation of a series of calcium carbonate polymorphs including disordered calcium carbonate, ikaite, vaterite, and calcite, which serve as nucleation sites for the formation of a calcium carbonate/calcium-silicate-hydrate (C-S-H) composite, and the subsequent acceleration of the curing process. The results from these studies reveal that in contrast to late-stage cement carbonation processes, these early stage (precure) out-of-equilibrium carbonation reactions do not compromise the material’s structural integrity, while allowing significant quantities of CO₂ (up to 15 w%) to be incorporated into the cementing matrix. The out-of-equilibrium carbonation of hydrating clinker thus provides an avenue for reducing the environmental footprint of cementitious materials via the uptake and long-term storage of anthropogenic CO₂.