Influence of Fiber Reinforcement on Restrained Shrinkage and Cracking

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Title: Influence of Fiber Reinforcement on Restrained Shrinkage and Cracking

Author(s): R. N. Swamy and H. Stavrides

Publication: Journal Proceedings

Volume: 76

Issue: 3

Appears on pages(s): 443-460

Keywords: cracking (fracturing); crack width and spacing; drying shrinkage; fiber reinforced concretes; fibers; glass fibers; metal fibers; shrinkage; synthetic fibers; tensile stress; tests.

Date: 3/1/1979

Abstract:
Drying shrinkage, when restrained, contributes to nearly all the cracking observed in concrete members before loading. A free shrinkage test cannot therefore give the true potential of fiber reinforcement to resist restrained shrinkage stresses and to control shrinkage cracking. A ring type of restrained shrinkage test is reported to demonstrate the ability of short, discrete fibers such as polypropylene, glass, and steel to control cracking and resist tensile stresses arising from restrained shrinkage. Three series of free and restrained shrinkage tests are reported with different matrices, types of fibers, and fiber contents. It is shown that the presence of fibers exercises a clear but small restraint to free shrinkage, and reduces drying shrinkage by up to 20 percent. When shrinkage is restrained, fiber reinforcement delays the formation of the first crack, prevents sudden failure observed with unreinforced matrices, enables the composite to suffer multiple cracking without failure, and reduces crack widths substantially. The fiber reinforced specimens were able to resist 50 to 100 percent more tensile stresses, and continued to resist the shrinkage stresses even after 8 to 12 months.