期刊
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
卷 105, 期 11, 页码 6924-6937出版社
WILEY
DOI: 10.1111/jace.18624
关键词
aging; Al-tobermorite; calcium silicate hydrates; X-ray methods
资金
- Ministry of Economy, Trade and Industry of Japan
- Nanotechnology Platform Program (Molecule and Material Synthesis Platform)
- Nanotechnology Platform Program (Advanced Characterization Nanotechnology Platform)
By studying a slice of a concrete wall in a nuclear power plant, the formation mechanism of Al-tobermorite was identified and it was found that Al-tobermorite forms almost everywhere in the cement paste with a uniform composition.
In modern Portland cement, calcium aluminum silicate hydrates (C-A-S-H) do not generally form crystalline Al-tobermorite. In this study, to identify the mechanism of Al-tobermorite formation, synchrotron micro X-ray diffraction and field-emission scanning electron microscopy-based energy-dispersive X-ray spectroscopy (EDS) investigations were performed on a slice of a thick concrete wall in a nuclear power plant, where the presence of Al-tobermorite was previously confirmed. Rietveld analysis of the diffraction diagrams obtained from the 2D diffraction patterns showed that Al-tobermorite was formed almost everywhere in the cement paste near sandstone aggregate and that Al-tobermorite platelets were distributed across most of the cement paste area in a random orientation. The basal spacing d-value of Al-tobermorite was identical and equal to 11.39 angstrom. The ratio plots from the EDS maps indicated that the chemical composition of the mixture of Al-tobermorite and C-A-S-H was almost homogeneous all around the cement paste. The Al-tobermorite in this concrete is probably formed via a dissolution-precipitation process. From the random orientation even next to the surface of aggregate, we infer that the Al-tobermorite formation does not need the surface of aggregate to precipitate.
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