Combined effect of fibre geometry and aggregate size on the workability and mechanical properties of steel fibre reinforced concrete

Reinforcing concrete with thin short discrete steel fibres is an efficient process in obtaining a multi-directional reinforcement to modify and improve the properties of concrete, especially its ductility. Therefore, it is imperative to understand the preference and selection of materials to make appropriate mixes for an efficient result of steel fibre reinforced concrete. This study investigates the effects of length and aspect ratio of steel fibres when mixed with different sizes of coarse aggregate on the workability and subsequently, on the mechanical properties of the material. Variables selected for the study were fibre lengths of 50 mm and 60 mm, aspect ratios of 45, 50 and 60, fibre dosages of 25 kg/m³, 40 kg/m³, 50 kg/m³ and 60 kg/m³ and maximum aggregate sizes of 10 mm and 20 mm. Mix proportions for the investigation were kept constant throughout the study. A slump test was performed on fresh concrete while the compressive strength was measured using 100 mm cubes and flexural performance was assessed through a 150 mm x 150 mm x 600 mm prism. The experimental results confirm that the combination of geometry and maximum aggregate size in the mix has an important influence on the workability of fresh steel fibre reinforced concrete. Consequently, the obtained results confirm that there is a relationship between the mechanical properties of hardened concrete and the workability of fresh concrete. The concrete with poor workability reveals inadequate orientation and distribution of fibres, leading to poor actions of fibres within the mix and hence, affecting the mechanical properties of tested concrete materials.