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Fracture processes of hybrid fiber-reinforced mortar

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Abstract

Subregion Scanning Computer Vision (SSCV), a digital image based method for measuring surface deformation is used to examine the role of the fibers in the fracture process of mortars reinforced with hybrid blends of microfiber (less than 22 μm in diameter) and macrofiber (500 μm in diameter). Closely-spaced microfibers interact with cracks at the microstructural level and hamper the widening of coalesced microcracks, thus encouraging the growth of multiple cracks. The microfibers improved pre-peak mechanical performance and strength by delaying the formation of a through-specimen macrocrack. Macrofibers were most effective at bridging macrocracks and imparting ductility to the composite due to their geometry and greater length. Compared to mortar reinforced with a single fiber type, an increase in strength and toughness was seen with a blend of steel macrofibers and either steel or PVA microfibers. Finally, based on the crack topography observed, the reduction in water permeability of cracked mortar achieved with hybrid fiber-reinforcement, measured directly in a parallel study, was governed by multiple crack development.

Résumé

La visualisation assistée par ordinateur (en anglais Subregion Scanning Computer Vision (SSCV), méthode basée sur les images numériques pour mesurer les déformations de surface, est utilisée ici pour examiner les processus de fissuration de mortiers de ciment renforcés à l’aide de mélanges hybrides de fibres: microfibres (diamètre inférieur à 22μm) et macrofibres (diamètre supérieur à 500μm). Les microfibres faiblement espacées interagissent avec les microfissures et rendent difficile l’élargissement de celles-ci et leur éventuelle union en fissures plus importantes. Ces microfibres ont amélioré les performances mécaniques et la résistance du mortier en deçà de la contrainte de rupture en retardant l’apparition de macrofissures traversant l’ensemble de l’échantillon.

Les macrofibres ont été les plus efficaces pour «coudre» les macrofissures tout en conférant une ductilité accrue au composite en raison de leur géométrie et de leur longueur plus importantes. Par comparaison avec des mortiers renforcés avec un seul type de fibre, ceux renforcés avec un mélange de macrofibres en acier et microfibres en alcool polyvinylique (PVA) ont révélé une résistance et une robustesse accrues.

Le renforcement avec un mélange hybride de fibres a permis aussi d’observer une diminution de la perméabilité du mortier fissuré. Cette diminution de perméabilité est due au développement d’une fissuration multiple par opposition a des microfissures qui se transforment en macrofissures.

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Authors and Affiliations

  1. Wiss, Janney, Elstmer, Associates Inc., 60062, Northbrook, IL, USA

    J. S. Lawler

  2. Institute for Concrete Structures and Building Materials, Darmstadt University of Technology, Alexanderstr. 5, 64283, Darmstadt, Germany

    T. Wilhelm

  3. MBT (Schweiz) AG, Vulkanstrasse 110, CH-8048, Zurich, Switzerland

    D. Zampini

  4. Dept. of Civil Engineering, Northwestern University, 60201, Evanston, IL, USA

    S. P. Shah

Authors
  1. J. S. Lawler
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  2. T. Wilhelm
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  3. D. Zampini
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  4. S. P. Shah
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Additional information

Editorial Note Prof. Dr. Surendra P. Shah is a RILEM Senior Member and participates in RILEM TCs 162-TDF ‘Test and design methods for steel fibre reinforced concrete’, ATC ‘Advanced testing of cement-based materials during setting and hardening’ and SOC ‘Experimental determination of the stress-crack opening curve for concrete in tension’. Prof. Shah is a member of the Bureau of RILEM as well as the Editor-in-Chief ofMaterials and Structures. ACBM Center (Northwestern University) is a RILEM Titular Member.

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Lawler, J.S., Wilhelm, T., Zampini, D. et al. Fracture processes of hybrid fiber-reinforced mortar. Mat. Struct. 36, 197–208 (2003). https://doi.org/10.1007/BF02479558

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