Flexural Strength and Toughness of Steel Fiber High-Strength Concrete

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Title: Flexural Strength and Toughness of Steel Fiber High-Strength Concrete

Author(s): Mahmoud A. lmam

Publication: Special Publication

Volume: 172

Issue:

Appears on pages(s): 517-534

Keywords: Bending; composite materials; fibers; flexural strength; high-strength concretes; toughness

Date: 12/1/1999

Abstract:
Experimental tests were carried out on 150* 150*600 mm high strength concrete beams containing 1.0% of hooked-end steel fibers. Concrete with compressive strength up to 117 MPa was used. The test results showed that the first-crack strength depends primarily on plain concrete characteristics rather than fiber parameters. After the occurrence of the first-crack, the fibers effectively work, carry the entire applied load, and tend to suppress the localization of micro-cracks into macro-cracks and consequently the flexural strength increases. Two equations are proposed for predicting the flexural strength of high strength concrete with and without fibers. The test results indicated that the use of 78 kg/m’ of hooked type steel fiber can easily provide toughness indices as high as 5, 10, and 30 for I5 , I10 , and I30 respectively. However, toughness Indices at higher deflection, such as I5 0 and I100 depending on service conditions are highly desirable to fully identify differences present in the load-deflection (P-6) curve. The relative post-crack strength helps to distinguish post-crack performance differences more clearly than toughness index because it reflects the shape of the P-6 curve over a specific deflection interval, rather than over the whole of the post-crack portion of the curve.