What is it about?
This paper presents an analytical model describing how steel (rigid) and synthetic (flexible) fibres are distributed in concrete. The number of fibres intersecting a cracked cross-section is a key parameter because it strongly influences the residual strength of fibre-reinforced concrete and the interpretation of beam tests. The study analyses how fibre orientation, mixing, and the interaction with the formwork (wall-effect) influence this number. Since steel fibres tend to rotate near the formwork while synthetic fibres bend, their behaviour differs significantly. The proposed model captures these mechanisms and predicts how many fibres effectively cross a crack, which can then be compared with experimental measurements.
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Why is it important?
The structural performance of fibre-reinforced concrete depends strongly on how many fibres actually cross a crack and how they are oriented. However, fibre distribution inside concrete is not perfectly uniform, and it is influenced by casting, mixing, and the interaction with the formwork. These effects can significantly change the number of fibres intersecting the cracked cross-section and therefore the measured material behaviour. By providing an analytical model that accounts for these mechanisms—including the different behaviour of rigid steel fibres and flexible synthetic fibres—the study helps engineers better interpret experimental results and improve material models used in structural design and numerical simulations.
Perspectives
The presented model provides a fundamental framework for understanding fibre orientation and distribution in concrete, which are key parameters controlling the mechanical behaviour of fibre-reinforced concrete. Recognizing the importance of fibre orientation helps explain the variability of experimental results and improves the interpretation of beam tests and material parameters. Because of this, the work can serve as a basis for further research, supporting the development of more advanced material models and evaluation methods. A better understanding of fibre orientation will ultimately contribute to more reliable design approaches for both steel and synthetic fibre reinforced concrete structures.
Dr Karoly Peter Juhasz
JKP Static Ltd
Read the Original
This page is a summary of: Analytical model for rigid (steel) and flexible (synthetic) fibre mixing in concrete, IOP Conference Series Materials Science and Engineering, August 2019, Institute of Physics Publishing,
DOI: 10.1088/1757-899x/596/1/012003.
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