The orientation of steel fibres affects the flexural performance of fibre-reinforced concrete. In this paper, selected experimental methods for the characterization of fibre orientation are evaluated and the relationship between residual flexural tensile strength and fibre orientation is discussed. To illustrate the applicability of the methods, the impact of the formwork surface on fibre orientation in slabs cast with fibre-reinforced self-compacting concrete (slump-flow class SF1 according to EN206) was investigated for the cases of formwork surfaces with slip, semi-slip and rough condition. The comparison of fibre orientation quantification methods showed good agreement between X-ray computed tomography and image analysis of sections from sawn beams. The variation in fibre orientation over the slab thickness was strongly influenced by the flow and the roughness of the formwork surface. The Thorenfeldt model for the impact of the fibre orientation factor on residual flexural tensile strength (used in the Norwegian proposal for fibre concrete guidelines) was verified and showed good agreement.
- Fibre orientation
- Fibre-reinforced concrete
- Image analysis
- Residual flexural tensile strength
- X-ray computed tomography (CT)