Grip-specimen interaction in uniaxial restrained test

Salah A. Altoubat, David A. Lange

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Restrained tests are used to evaluate the risk of early age cracking and the cracking sensitivity of concrete mixtures. One test that has become common in recent years is the active uniaxial restrained test in which the length change due to shrinkage is recovered by applying external load to maintain the concrete sample at constant length. The length change is measured by linear variable differential transformer (LVDT), which is used as the control signal in this test. In such tests, the dog-bone geometry is used to grip the ends. To ensure a fully restrained test, the LVDT response to the loads and to shrinkage should reflect the deformation in the concrete sample. Therefore, the gripspecimen interaction should not interfere with the measurement of deformation, and this depends on the instrumentation and how the LVDT is attached to the concrete specimen. Some experiments in the literature have the LVDT attached to the steel grips, a practice vulnerable to possible error due to the interaction between the grip and the concrete. This study considered two methods of attaching the LVDT. First, the LVDT is attached to the steel grips; second, the LVDT is attached to the concrete within the zone of reduced cross-section. The results indicate that attaching the LVDT to the grips results in errant measurement of the shrinkage stress, creep, and elastic strains due to the gripspecimen interaction. The consequences will be false interpretation of fully restrained shrinkage and creep characteristics because the grip-specimen interaction leads to a partially restrained test. The study suggests mounting the LVDT to the concrete sample away from the grips to achieve a fully restrained test. Results for two concrete mixtures with w/c ratio of 0.51 and 0.56 are discussed for both methods of attaching LVDTs.

Original languageEnglish (US)
Title of host publicationConcrete
Subtitle of host publicationMaterial Science to Application - A Tribute to Surendra P. Shah
PublisherAmerican Concrete Institute
Pages189-203
Number of pages15
ISBN (Electronic)9780870310751
StatePublished - Apr 1 2002

Publication series

NameAmerican Concrete Institute, ACI Special Publication
VolumeSP-206
ISSN (Print)0193-2527

Keywords

  • End effects
  • Restrained shrinkage
  • Shrinkage
  • Tensile creep
  • Tensile test

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Building and Construction
  • General Materials Science

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