Abstract
For the determination of the performance of steel-fiber reinforced concrete (SFRC), the post-peak flexural strengths are used. In different national and European standards, different test-setups are defined, resulting in double efforts for testing for the manufacturers. In addition, the German national guideline "Stahlfaserbeton (DAfStb)" on SFRC is well established European-wide, but the test standard is specifically national, demanding a four-point-bending tests using unnotched beams. Contrarily, the European standard EN 14651 as well as the Model Code 2010 demand three-point bending tests using notched specimens. Applying the national guideline is obligatory in Germany for structural use of SFRC. Therefore, it is essential to standardize the performance evaluation of SFRC based on commonly applied international guidelines. In the following, an approach is presented especially dealing with the problem of random occurrence of cracks in the four-point-bending tests. It is shown, that neglecting the point of crack can systematically under-estimate the performance of SFRC especially at deformations.
Highlights
In order to get permission to distribute and sell steelfibers in Europe, a CE-certificate is obligatory
In order to get the permission to sell steel-fiber reinforced concrete e.g. as ready mixed concrete the performance of SFRC has to be evaluated according to the German national guideline "Stahlfaserbeton (DAfStb)" [3]
Because the correction at δ = 0.5 mm is small, the post-peak flexural strength values are unaffected for a large number of beams
Summary
In order to get permission to distribute and sell steelfibers in Europe, a CE-certificate is obligatory. It is necessary to determine the performance of the steel-fibers in concrete, depending on the type of steel fibers as well as the fiber contents In this case, the EN 14651 [2] is the relevant standard, demanding a test using third-point loading on notched specimens. Seen from the mechanical point of view the evaluation of post-peak flexural strengths is a fracture mechanical problem, demanding determination of strengths and load bearing capacities directly in the crack. This precondition is fulfilled only by EN 14651 but not by the German guideline, because the crack can occur anywhere in the mid third of the beam due to the four-point-loading scheme.
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