Journal of Advanced Concrete Technology
Online ISSN : 1347-3913
ISSN-L : 1346-8014
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Scientific paper
  • Ippei Maruyama, Jiří Rymeš
    2019 Volume 17 Issue 5 Pages 188-194
    Published: May 09, 2019
    Released: May 09, 2019

    Short-term length-change isotherms and desorption isotherms of matured hardened cement paste were measured at different temperature conditions, namely, 20, 30, 40, 50, and 60℃. For the short-term length-change isotherms, higher temperature conditions resulted in a smaller drying shrinkage. This trend was largely controlled by the microstructural reorganization of the calcium-silicate-hydrates in the cement paste at elevated temperatures. The experimental results suggest that a portion of the evaporable water did not contribute to the shrinkage. In addition, based on the relation-ships between the incremental strain and the incremental evaporable water content, with a starting relative humidity of 5%, consistent trends were observed for the incremental strain and the incremental evaporable water when the incremental evaporable water content was less than 0.08 g/g-dried hcp. The microstructural reorganization pathways for elevated temperature and/or for drying were confirmed to be identical.

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  • Jiří Rymeš, Ippei Maruyama, Ryu Shimamoto, Atsushi Tachibana, Yoshihit ...
    2019 Volume 17 Issue 5 Pages 195-215
    Published: May 09, 2019
    Released: May 09, 2019

    A variation of material properties with depth is observed in a massive, seismic-resistant internal wall of Unit 1 of the Hamaoka Nuclear Power Plant (NPP) 45 years after its construction. The maximum values are attained in the center of the structural element and gradually decrease towards the surface, while still well exceeding the required performance. It is found that this trend can be mostly attributed to the reaction between cement hydrates and rock-forming minerals of a feldspar group, which releases silica and alumina oxides into the pore solution, where they react with portlandite to form new hydrates. No evidence of expansive distress similar to the alkali-silica reaction (ASR) is found in the material, owing to this reaction. Possible implications for the aging management of existing concrete structures are discussed.

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