Is Superposition of Creep Strains Valid for Concretes Subjected to Drying Creep?

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Title: Is Superposition of Creep Strains Valid for Concretes Subjected to Drying Creep?

Author(s): N. J. Gardner and H. Tsuruta

Publication: Materials Journal

Volume: 101

Issue: 5

Appears on pages(s): 409-415

Keywords: concrete; creep; strain

Date: 9/1/2004

Abstract:
This paper describes an experimental investigation to study the validity of superposition of creep strains for specimens subjected to drying before loading, loading before drying, and sealed specimens subjected to uniaxial compression. Self-consolidating concrete was used for ease of fabrication. Strains were measured using vibrating wire strain gages. In all three conditions, (drying before loading, loading before drying, and sealed concrete), creep recovery is only 70 to 80% of the creep of previously unloaded concrete for loads applied at the same age as the recovery. It can be concluded that superposition is not valid for concrete subjected to drying or sealed concrete for situations that involve unloading. For increasing loads, the validity of the principle of superposition of creep strains depends upon whether the concrete is sealed or subjected to drying. For drying before loading and loading before drying, the measured incremental creeps were 10 and 20% larger, respectively, than the creep of late loaded specimens. For sealed concrete, the creep due to an incremental increase in load was effectively identical to the creep of sealed, late-loaded concrete. Examination of the experimental results suggests an alternative hypothesis to calculate the strains recovered on unloading. The rates of development and magnitudes of the recovered creep strains were similar for all test series, suggesting that only basic creep can be recovered.