Effectiveness Near Boundaries of Fibre Reinforcement in Concrete: Fid-Bau Portal

Effectiveness Near Boundaries of Fibre Reinforcement in Concrete

Stroeven, P. / Hu, J.

Abstract Materials testing of relatively small specimens can lead to biases due to disturbances in fibre reinforcement near external surfaces. This paper presents a complete methodological framework for investigating reinforcement characteristics in bulk and in boundary zones. The developed model assumes actual fibre dispersion a mixture of 3D, 2D and 1D portions. Mostly, the 1D component is small, so that a partially planar fibre composite is resulting. Separate expressions for 2D and 3D portions are obtained for the average projected fibre length (tangent height) that governs fibre characteristics in sections (for image analysis purposes), and for the average embedment characteristics that are at the basis of the stress transfer capability. Crack opening in concrete is assumed counteracted by friction between fibres and matrix pockets. However, additional mechanisms can easily be incorporated. Plain cylindrical steel fibres, eventually curved, were envisaged, but anchoring facilities and arbitrary cross sections could be dealt with, as well. Expressions are given for stress transfer capability (strength) in bulk and in boundary zones. Most of the boundary effects are restricted to a zone half the fibre length in width. Magnitude of strength reduction in this zone is of the order of 10%.