The addition of discontinuous discrete fibres to concrete has repeatedly been shown as an effective method to overcome the inherently brittle nature of concrete. The resulting composite has enhanced toughness and impact resistance and is broadly referred to as Fibre-Reinforced Concrete (FRC). Although the benefits of implementing FRC are evident, the high variability associated with FRC has frequently been cited as a characteristic stunting vast structural application of the material. This research is focussed on the spatial distribution of fibres and the way it affects flexural performance. A thorough understanding of the influence of fibre spatial distribution on composite performance is the first step in incorporating fibre distribution into material and structural design procedures and aids the pursuit of effective and optimal implementation of FRC in practice.
The study was aimed at not only investigating the influence of fibre distribution on flexural performance but also evaluating the effect of fibre length and volume content on the fibre spatial characteristics.
The experimental framework considered two hook-ended steel fibres with different lengths incorporated into a 50 MPa concrete mixture at volume contents ranging from 40 kg/m3 to 120 kg/m3. Flexural response was obtained using three-point bending tests on notched specimen, after which each specimen was cut adjacent to the crack plane and prepared for image analysis. An image processing algorithm was developed to automatically extract the fibre locations that were used to describe the fibre spatial characteristics.
Spatial distribution was explored by evaluating the uniformity of fibres across a section, the inter-batch variability of fibre distribution, and the degree of clustering. A geometric descriptor of fibre spacing was defined using Voronoi diagrams generated from image data and employed in a unique approach developed for quantifying fibre spatial characteristics. An alternative approach was developed and used to compare the spatial metrics resulting from the Voronoi approach. The findings of the study highlight the role of fibre length and content on the spatial distribution of fibres and it is revealed that the sectional uniformity, inter-batch spatial variability, and degree of clustering are dependent on the number of fibres in the cross section.
Furthermore, the results demonstrate the substantial influence of fibre distribution on the flexural performance of FRC. It is concluded that the variability in flexural strength reduces as the variation in fibre spatial distribution reduces and that extensive clustering has an adverse effect on the effective resistance provided by fibres.
Dissertation (MEng)--University of Pretoria, 2018.