Flowable fibre-reinforced concrete for structural applications: A modelling approach that can take anisotropic and inhomogeneous fibre configuration into account

摘要

The fibre orientation and distribution in a structural element cast with flowable fibrereinforcedconcrete (FRC) is affected by the concrete flow, which can enhance its nonuniformand anisotropic fibre configuration. The structural behaviour may deviatesubstantially, in favourable or unfavourable ways, from behaviour corresponding to auniform and isotropic fibre configuration, or from behaviour measured in a materialcharacterization test.The aim of this research project was to evaluate the impact of the fibre configuration onthe mechanical behaviour of elements cast with flowable FRC and to provide amethodology for predicting this effect in their structural behaviour. The experimentalinvestigation focused on characterizing the fibre volume content and orientation tomake it possible to explain the structural behaviour. The examination was done at twolevels of application: at the full-scale level using structural beams, and at a small-scalelevel using test specimens for material characterization.The analysis of the fibre configuration at the full-scale level confirmed that castingunder full-scale conditions can lead to non-uniform fibre configurations which may bedifficult to foresee in the production stage and may not occur in standard test specimens.The observed non-uniform fibre configuration in the full-scale beams had a directconsequence on their mechanical response; the areas with unfavourable orientation andlow fibre content played a decisive role in the crack propagation and reduced the loadcarryingcapacity. These observations suggest that procedures for estimating thestructural performance of flowable FRC need to consider determinations or predictionsof its fibre configuration.From a design-oriented perspective, one possible approach is to characterize thematerial using small-scale standard tests and correct these results for favourable orunfavourable variations in fibre content and fibre orientation in the full-scale element.As a more advanced solution, a numerical modelling approach was developed to predictthe mechanical response of a structural element taking its actual fibre configuration intoaccount. This approach was found to capture the large differences in the loadingcapacity of the beams tested, which can only be attributed to the differences in theirfibre configurations.Incorporating the effect of fibre configuration in the prediction of structural behaviourwill contribute to more reliable and effective use of flowable FRC. In combination withsimulations of casting and non-destructive methods of characterizing the fibreconfiguration, this will encourage the use of this material in structural applications.