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@PHDTHESIS{Cleven:961553,
      author       = {Cleven, Simon},
      othercontributors = {Matschei, Thomas and Dehn, Frank},
      title        = {{D}evelopment of a novel test setup for the determination
                      of the content and orientation of steel fibres in concrete
                      based on electrical resistivity},
      school       = {Rheinisch-Westfälische Technische Hochschule Aachen},
      type         = {Dissertation},
      address      = {Aachen},
      publisher    = {RWTH Aachen University},
      reportid     = {RWTH-2023-06873},
      pages        = {1 Online-Ressource : Illustrationen, Diagramme},
      year         = {2023},
      note         = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
                      University; Dissertation, Rheinisch-Westfälische Technische
                      Hochschule Aachen, 2023},
      abstract     = {Steel fibre reinforced concrete (SFRC) has the potential to
                      be used for versatile applications in a cost-efficient and
                      resource-saving way. One of the biggest obstacles for
                      further application at present is that the fibre content,
                      fibre distribution and fibre orientation cannot be
                      determined exactly. Although the global fibre content can be
                      calculated from total fibre addition in the manufacturing
                      plant, local differences regarding the fibre content within
                      the material arising from formwork geometry or other factors
                      remain difficult to quantify. Moreover, only assumptions can
                      be made regarding the distribution and orientation of
                      fibres. As a consequence, high partial safety factors have
                      to be applied for the static design of structural elements,
                      which prevents an economic use of steel fibre concrete in
                      many cases. To address this challenge, the main objective of
                      this thesis was the development of an easy-to-use
                      measurement approach that enables the determination of the
                      above-mentioned parameters. Based on an in-depth literature
                      review, the electrical resistivity measurement was
                      identified as a promising approach for the measurement
                      methodology. After identifying the decisive influencing
                      factors from the measurement principle and the material
                      SFRC, a prototype test setup for cubic specimens was
                      developed and tested. Following an extensive parameter study
                      to optimize the measurement system, the setup was extended
                      to include cylindrical specimens, allowing for the
                      examination of drilling cores. Using a two-electrode setup
                      with an alternating current application in a frequency range
                      of 1 to 10 kHz, the electrical resistance measurements
                      yielded positive outcomes. Lower frequencies led to
                      time-dependent measurement errors, which can be attributed
                      to a polarisation at the electrodes. To analyse the
                      measurement results, it is necessary to convert the measured
                      electrical resistances into geometry-independent electrical
                      resistivities. Geometry factors for specific electrode
                      arrangements can be obtained with help of FEM simulations,
                      coupled to a multiphysics-software. By comparing the
                      electrical resistivities of the SFRC with a plain reference
                      concrete, the steel fibre content can be determined with
                      sufficient accuracy. The estimation of the fibre orientation
                      was possible by the relation of different measuring
                      directions of a sample. The greatest challenge for the
                      further development of the measurement system was identified
                      with the need for a reference concrete or knowledge of its
                      electrical resistivity. The focus of future investigations
                      must therefore be on the creation of a material
                      parameter-dependent database so that an analysis of
                      structural concretes can be realised. In addition, it is
                      necessary to transfer the prototype measuring system into a
                      system with well-defined coupling and measuring conditions.
                      After the successful development and adaptation of these
                      factors, the measurement methodology may be transferred to a
                      general guideline and/or standard in order to be able to
                      realise new static design principles with lower partial
                      safety factors. This will enable material-efficient design
                      principles for steel fibre reinforced concrete in the
                      future.},
      cin          = {311110},
      ddc          = {624},
      cid          = {$I:(DE-82)311110_20160603$},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.18154/RWTH-2023-06873},
      url          = {https://publications.rwth-aachen.de/record/961553},
}