Tensile Strain Hardening and Multiple Cracking in High-Performance Cement-Based Composites Containing Discontinuous Fibers

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Title: Tensile Strain Hardening and Multiple Cracking in High-Performance Cement-Based Composites Containing Discontinuous Fibers

Author(s): Prijatmadi Tjiptobroto and Will Hansen

Publication: Materials Journal

Volume: 90

Issue: 1

Appears on pages(s): 16-25

Keywords: concretes; cracking (fracturing); fiber reinforced concretes; fibers; strain hardening; strains; Materials Research

DOI: 10.14359/4031

Date: 1/1/1993

Abstract:
The mechanism responsible for the improvement in tensile strain capacity of fiber reinforced concrete (FRC) as a result of the addition of high volume fraction of fibers is investigated. From experiments using fiber reinforced densified small particles (DSP) containing high volume fraction (higher than 3 percent) of fine and short steel fibers, it was found that the formation of multiple microcracking, which occurs between the point of first cracking and the peak load, was the main cause for the improvement in total strain capacity. This region, which is the inelastic strain region due to the microcracking, is a unique property of high-performance FRC. Multiple microcracking is a property of the bulk material, since no strain localization occurs. At 12 percent fiber volume fraction, a total strain capacity of about 0.2 percent was measured from flexural tests: an increase of about 15 to 20 times over that of the plain matrix. Also obtained was information on crack formation and the crack pattern. For FR-DSP in flexure, it was found that the first crack would eventually become the failure crack. An analytical approach, based on the energy changes associated with cracking, was used in explaining the occurrence of multiple microcracking. The energy terms considered include: matrix fracture energy, matrix strain energy, debonding energy, fiber strain energy, and fiber frictional energy. Assuming that the first crack is also the failure crack, the model predicts that multiple cracking occurs in high- performance FRC. In such composites, the energy needed to open the critical crack exceeds the energy needed to form a new crack. The analysis predicts that the major energy term determining this behavior is the fiber debonding energy. Also derived were predictions of the number of microcracks and the minimum fiber volume fraction needed for the occurrence of multiple microcracking.


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