In situ TEM observation of calcium silicate hydrate nanostructure at high temperatures

Journal Article · 23 August 2021 · Cement and Concrete Research

DOI: https://doi.org/10.1016/j.cemconres.2021.106579 · OSTI ID:1902111

Zheng, Qi ^[1]; Jiang, Jinyang ^[2]; Li, Xinle ^[3]; Bustillo, Karen C. ^[3]; Zheng, Haimei ^[4]

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1. Southeast Univ., Nanjing (China); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
2. Southeast Univ., Nanjing (China)
3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Foundry
4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Fire poses a substantial threat to concrete structures because calcium silicate hydrate (C-S-H) is not thermally stable at high temperatures. Herein, in situ TEM at temperatures from 20 to 800 °C was conducted to study the thermal-induced structural changes in C-S-H. In this work, we captured C-S-H shrinks at an average rate of 0.02 μm²/°C upon heating with three stages observed, including induction, constant, and rapid periods. Our observation revealed that an 800 nm pore could be healed during pore structure evolution owing to the reconstruction and deformation among C-S-H blocks. The Ca/Si ratio was dropped at higher temperatures because of the leakage of calcium ions from the C-S-H structure to form CaO precipitates. The temperature-driven phase transformation and degradation were also detected using electron diffraction that C-S-H was transformed into metastable calcium silicate minerals above 800 °C. This work provides insights into the nanoscale transformation of C-S-H at high temperatures.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). The Molecular Foundry (TMF)
• Sponsoring Organization: National Natural Science Foundation of China (NSFC); USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1902111
• Journal Information: Cement and Concrete Research, Journal Name: Cement and Concrete Research Vol. 149; ISSN 0008-8846
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English