Stefaniuk Damian, Hajduczek Marcin, Weaver James C, Ulm Franz J, Masic Admir
Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139, USA.
Wyss Institute for Biologically Inspired Engineering, Harvard University, 3 Blackfan St, Boston, MA 02115, USA.
PNAS Nexus. 2023 Mar 28;2(3):pgad052. doi: 10.1093/pnasnexus/pgad052. eCollection 2023 Mar.
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 CO 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 CO (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 CO.
解决普通波特兰水泥生产中与温室气体排放相关的现有缓解策略与2050年碳中和目标之间的差距是一项重大挑战。为了弥合这一差距，一个潜在的选择是通过在胶凝矿物及其骨料中进行强制碳酸矿化，将人为产生的二氧化碳直接气态封存于混凝土中。为了更好地阐明这些过程的潜在战略益处，在此，我们应用一种综合的、具有时间和空间分辨能力的拉曼显微镜和压痕方法，以碳酸氢盐取代的阿利特为模型系统，研究从最初几小时到几天时间尺度内水泥碳酸化的潜在机制和化学力学。在这些反应中，水化位点处瞬态无序氢氧化钙颗粒的碳酸化导致形成一系列碳酸钙多晶型物，包括无序碳酸钙、六水碳酸钙、球霰石和方解石，这些多晶型物作为碳酸钙/硅酸钙水化物（C-S-H）复合材料形成的成核位点，并随后加速固化过程。这些研究结果表明，与后期水泥碳酸化过程不同，这些早期（预固化）非平衡碳酸化反应不会损害材料的结构完整性，同时允许大量的二氧化碳（高达15重量%）掺入胶凝基体中。因此，水化熟料的非平衡碳酸化为通过吸收和长期储存人为产生的二氧化碳来减少胶凝材料的环境足迹提供了一条途径。
