A New Look at Tensile Creep of Fiber-Reinforced Concrete

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Title: A New Look at Tensile Creep of Fiber-Reinforced Concrete

Author(s): S. A. Altoubat and D. A. Lange

Publication: Special Publication

Volume: 216

Issue:

Appears on pages(s): 143-160

Keywords: basic creep; curing; drying creep; early age behavior; fiber reinforcement; restrained shrinkage; shrinkage cracking; shrinkage stress; steel fibers; tensile creep

Date: 10/1/2003

Abstract:
Creep of concrete is composed of basic and drying creep components, and the drying creep is primarily caused by two mechanisms: stress induced shrinkage and microcracking. The effects of steel fibers on basic creep, stress induced shrinkage, and microcracking components for two concrete mixtures with w/c of 0.4 and 0.5 are discussed. The steel fibers were found to enhance the basic creep mechanisms and reduce the drying creep mechanisms. The reduction in drying creep offsets the increase in basic creep leading to a net tensile creep similar for both plain concrete and FRC; a conventional conclusion that usually obscures the role of fibers on shrinkage stress relaxation and cracking. A new look that is consistent with material behavior is introduced by dividing the creep mechanisms into beneficial aspects associated with real creep mechanisms and detrimental aspects associated with apparent creep mechanisms (microcracking). Basic creep and stress-induced shrinkage are real creep mechanisms associated with deformation of hydration products, while microcracking is detrimental because of the associated microstructural damage. Steel fibers tend to enhance the beneficial mechanisms and reduce the detrimental ones, thus enhancing the overall performance. The results explain the difference in shrinkage cracking between plain concrete and FRC; an insight that would not be achieved by looking at total tensile creep alone.