Flowability of fibre-reinforced concrete and its effect on the mechanical properties of the material

Fibre distribution is an important factor, affecting both the fresh- and hardened-state properties of concrete. The paper describes a study in which the fibre distribution and orientation were investigated by means of a suitable technique, by using a translucent fluid model with a yield stress (Carbopol 940). The observation confirmed the ability of the developed method to provide data on the orientation and distribution of steel fibres within concrete. It was showed that orientation and distribution are dependent on the yield stress of the fluid material. Concrete specimens, containing 0.5% of 35 mm long hooked steel fibres, were also cast and tested under four-point loading, in order to study the correlation between rheology, fibre distribution and the mechanical properties of steel fiber-reinforced concrete. The results confirm that the rheology of concrete has an important influence on the orientation of the fibres. The flexural strength depends on the fibre distribution and orientation and is significantly improved when the fibres are oriented in the direction of the tensile stresses fresh (concrete with good workability). On the contrary, for concrete with poor workability, an inadequate orientation of fibres occurred, leading to a poor contribution of the fibres to the flexural behaviour of the tested specimens, despite the relatively higher compression strength of the tested concrete material.