Conclusions

In this paper, results are reported of a study which investigated the mechanism causing the time-dependant crack widening of cracked steel fibre reinforced concrete members. Rate and creep tests were done by pulling out single fibres and uni-axial tensile creep tests were also done. The mechanisms causing this time-dependant deformation is not yet fully understood, however, the following conclusions can be made based on the work presented here:

  • - Single fibre pull-out tests can be used to investigate the creep behaviour of cracked steel fibre reinforced concrete.
  • - For the range tested, it was found that the pull-out rate does not affect the maximum pull-out resistance of hooked-end steel fibres. However, the pull-out displacement at the point of maximum pull-out resistance was increased by 22 % over five orders of magnitude of the pull-out rate.
  • - Both the single fibre pull-out creep results and the uni-axial tensile creep results showed that the time-dependant displacements are proportional to a load level of at least 50 % of the ultimate resistance after which it increases non-linearly.
  • - It was shown that micro-cracking is responsible for this non-linear increase of pull-out creep.
  • - Based on the rate test results of the single fibre pull-out, the micro-CT images and the pre-damaged single fibre pull-out creep tests it can be deduced that the interfacial transition zone between the fibre hooked-end and the matrix plays and important role in the creep of cracked fibre reinforced concrete.
 
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