A review on the assessment and prediction of the orientation and distribution of fibres for concrete

Fibres that cross the fracture surface govern the performance of fibre reinforced concrete (FRC), playing a major role in fracture results used to evaluate the structural competence of the composite material. Thus, FRC post-cracking behaviour is related to the number of fibres acting in the cracked surface and their forming angle. Both orientation and distribution of the fibres have been evaluated with several experimental techniques, while various models have assessed the prediction of such fibre positioning by using the orientation factor. This study aims to review the existing models found in the literature and improve their use to predict fibre positioning. Early models showed that the stereographical model could serve as a powerful tool as regards rigid fibres, whereas recent ones have assessed macro-synthetic fibre orientation and distribution. In addition, several external regular and standardised conditions that have been shown to affect the positioning of fibres are considered. The main sources of anisotropy are addressed: fresh-state properties of the concrete, pouring methods, compaction procedures, wall-effects and formwork geometries. In this review, practical tools and information extracted from the models are supplied that provide an interesting overview about predicting the orientation factor.