Creep and shrinkage at variable hygric exposures
Final Report Abstract
The expected long-term deformations of concrete structures are calculated using prediction models, which are almost entirely based on results obtained under constant loading and constant climatic conditions. In practice, however, concrete structures are frequently subjected to cyclic exposures, both with regard to mechanical loadings as well as ambient humidity conditions. Cases of damage reported give considerable reason to suspect that the assumption of constant exposures lead to a significant underestimation of the deformations that actually occur. In the joint research project reported here, the influences of cyclic-mechanical (SWK) and cyclic-hygric exposures (FWK) on the long-term deformations of concrete were investigated. The overall objective of the FWK-part of the project presented here was to quantify the influence of cyclic ambient humidity with special attention paid to the influence of the initial moisture content on the long-term deformation behaviour of concrete and improve the existing design approaches. The results obtained at constant ambient humidity conditions showed that the initial moisture content has a significant influence on the long-term deformation behaviour of concrete, so that the drying shrinkage and creep, but also the basic creep, increased with higher initial moisture contents. Furthermore, creep strains are significantly increased up to 60 % at the end of loading due to cyclic ambient humidity compared to creep strains at RHmean and this effect increased in percentage terms with lower initial moisture contents. These results reveal that the assumption of a constant mean ambient humidity (time-average) for the calculation of creep strains is not suitable and that it is necessary to consider directly the influence of the moisture content in the design of the basic creep, drying creep and shrinkage.
Publications
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Creep and shrinkage of concrete under cyclic ambient humidity conditions. Proceedings of the 2022 session of the 14th fib International PhD Symposium in Civil Engineering, 5-7 September 2022, Rome, Italy
Podhajecky, A.-L.; Oneschkow, N. & Haist, M.
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Influence of initial moisture content on creep and shrinkage of concrete at constant and cyclic ambient humidity. Materials and Structures, 56(9).
Podhajecky, Anna-Lena; Oneschkow, Nadja; Kern, Bianca; Lohaus, Ludger; Müller, Harald S. & Haist, Michael
