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Verification Test of Restoration Effect of Offshore Concrete Structure Using Permanent Formwork Panels and Underwater Inseparable Mortar


In recent years, the deterioration of harbor structures has become a matter for concern, and the establishment of effective repair methods has become urgent. In this study, a repair method for installing permanent formwork panels and filling them with underwater inseparable mortar is proposed as an effective section-restoring method for deteriorated concrete caisson sidewalls. To investigate the integrity between existing concrete and repaired parts as well as the effect of thickness increase due to panel installation, static bending tests of a flat-reinforced concrete (RC)-beam-modeled side wall used in caisson structures are conducted. The results obtained from this study are as follows: (1) by attaching the permanent formwork panels to the flat RC beam, the bending crack occurring load was improved by a factor of three, and the rebar yielding load and maximum load were doubled. This tendency was the same even when the RC beam had a cross-sectional defect. (2) The RC beam with the permanent formwork panels finally failed with diagonal cracks opening after the maximum load was reached. The ductility ratio at this time was approximately 6. To improve the deformation performance, it is necessary to apply shear reinforcement. (3) The analysis results by the fiber model assuming the complete adhesion of the permanent formwork panels, underwater inseparable mortar, and RC beam were performed, and the results were compared with the experimental results. As a result, it was clarified that the adhesion of each constituent material was retained until the yield of the main reinforcing bar. After that, pulling out of the main reinforcing bar from the concrete and damage to the permanent formwork panel became apparent. (4) The curvature of the cross-section at the yield of the main reinforcing bar was φyc = 0.007 m−1, and it was confirmed that the assumption of plane conservation was valid in the cross-section with a curvature less than that. This research is expected to promote the efficient maintenance of existing concrete caisson structures. As the amount of cement used and the construction period can be reduced, it is assumed that the environmental load can be reduced as well.

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We would like to thank Editage ( for English language editing.

Author information




Writing original draft, YK; conceptualization, MM; preparing one-half scale specimen, RN. All authors have read and agreed to the published version of the manuscript.

Corresponding author

Correspondence to Yusuke Kurihashi.

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The authors declare no conflicts of interest.

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Kurihashi, Y., Minami, M. & Nishiyauchi, R. Verification Test of Restoration Effect of Offshore Concrete Structure Using Permanent Formwork Panels and Underwater Inseparable Mortar. Int J Civ Eng 19, 1111–1124 (2021).

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  • Flat RC beam
  • Concrete caisson
  • Section restoring method
  • Permanent formwork panel
  • Underwater inseparable mortar