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Home arrow Engineering arrow Creep Behaviour in Cracked Sections of Fibre Reinforced Concrete: Proceedings of the International RILEM Workshop FRC-CREEP 2016
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Conclusions

Since the above described tests were one by one tailored to a specific applications, individual test results from different programs can’t be compared as such. More in depth analysis needs to be done to better understand creep in FRC materials, but before extra tests are performed, it is essential to agree on a single test setup that can give the material characteristics required for creep analysis in structural design. However, a number of important conclusions can be drawn from the research described above and some of them are helpful for the definition of a unified and improved test setup:

  • • Depending on the specimen type and test setup, the tested PFRC specimens show up to 4 times higher 5creep,m than the tested SFRC specimens.
  • • The majority of tested PFRC specimens fail under the applied sustained loading while none of the SFRC specimens collapse.
  • • SFRC with 3D and 5D steel fibres show similar creep behaviour.
  • • The time to failure of PFRC specimens cannot be predicted from the test data since it is varying a lot. Thus the tests need to be performed during a sufficiently long time range and need to include fibre characteristics such as shape and surface geometry.
  • • There are indications that higher fibre dosages result in additional deflection. This is most likely due to the higher absolute Fr which is achieved at higher fibre dosages.
  • • The initial crack width and Fcreep have an important effect on the creep behaviour.
  • • The combined effect of increased 5pc and increased Fcreep has been found to have a bigger impact for PFRC than for SFRC.
  • • Due to the indeterminate crack pattern in the plates, which is inherent to the fully supported setup, it is difficult to interpret the actual creep behaviour of the material, rather than that of the system. The initial test deflection and (final) crack pattern strongly affects the performance in the long term test setup. Additionally, external factors such as friction of test supports and arching is likely to have an influence. Therefore, interpreting results of these centrally loaded plates is a lot more complex than that of a notched beam according to EN14651. The indeterminate plate test appears less suitable for the comparisons of FRC material properties.
  • • The statically determinate beam tests with a clear load path, however, give an easily interpretable result. Especially the notched 3 point bending beam test based on EN14651 give allow for reproducible test results and identification of material properties. In addition, the underlying test method is already well known in the European industry (EN 14651).
  • • A potential effect of Fcreep on the short-term ultimate performance has not been investigated in the described tests.
  • • The effect of increased temperature levels has not been investigated in the described tests. In view of the thermoplastic material properties of most polymer macro fibres, this parameter should also be important and needs to be considered in an improved test setup.

References

  • 1. Hilaire, A., Benboudjema, F., Darquennes, A., Berthaud, Y., Nahas, G.: Analysis of concrete creep in compression, tension and bending: numerical modelling. Ninth International Conference on Creep, Shrinkage, and Durability Mechanics (CONCREEP-9)
  • 2. EN14651:2005: Test method for metallic fibred concrete. Measuring the flexural tensile strength (limit of proportionality (LOP), residual), 11 July 2005
  • 3. EN14488-5: Testing sprayed concrete—Part 5: determination of energy absorption capacity of fibre reinforced slab specimens, 27 Feb 2006
 
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