Application of WST-method for fracture testing of fibre-reinforced concrete (NT TR 575)

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  • Report #: NT TR 575
  • Approved: March 2005
  • Author(s): Ingemar Löfgren, John Forbes Olesen, Matias Flansbjer
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Abstract

To evaluate the reproducibility of the wedge-splitting test method and to provide guidelines, a round robin study was conducted in which three labs participated. The participating labs were DTU – the Technical University of Denmark, Department of Civil Engineering; CTH – Chalmers University of Technology, Department of Structural Engineering and Mechanics; and SP – the Swedish National Testing and Research Institute.

Two different mixes were investigated; the difference between the mixes was the fibre length (Mix 1 with 40 kg of 35 mm long fibres and Mix 2 with 40 kg of 60 mm long fibres). The test results from each lab were analysed and a study of the variation was performed. From the study of the intra-lab variations, it is evident that the variations of the steel fibre-reinforced concrete properties are significant. The coefficient of variance for the splitting load was found to vary between 20 to 40%. The investigation of the inter-lab variation, based on an analysis of variance (ANOVA) indicated that there is no inter-lab variation. The test result can be said to be independent of the testing location and the equipment used (with or without CMODcontrol).

The conclusions that can be drawn from this study are that:

  • the wedge-splitting test method is a suitable test method for assessment of fracture properties of steel fibre-reinforced concrete;
  • the test method is easy to handle and relatively fast to execute
  • the test can be run with CMOD-control or without, in a machine with a constant crosshead displacement rate (if rate is equal to or less than 0.25 mm/min);
  • due to variations in fibre distribution, the scatter of the test results is high;
  • the dimensions of the specimen (height, width, and thickness) should, if possible, be four times the maximum fibre length, or at least more than three times the fibre length;
  • using inverse analysis, the tensile fracture properties can be interpreted from the test result as a bi-linear stress-crack opening relationship.