Optimal properties of fresh ultra-high-performance concrete for homogeneous metallic fibre distribution

Abstract

As concrete is one of the most widely used construction materials on the planet, it is essential to adopt its properties for a wide range of applications. Its high compressive strength makes it the ideal material for compressive load-bearing structures, such as walls and columns. The low tensile strength and brittle behaviour are considered the biggest disadvantages that considerably limit the application of the material. However, this can be overcome, when additional reinforcement, such as metallic rebars or fibres with high tensile strength, is introduced into the concrete matrix. This allows for the prevention of brittle fractures when concrete is subjected to tensile stress. There are certain differences in the application technology between rebars and fibres. Metallic rebars are designed and placed in the mould according to calculated tensile loads, thus requiring special preparation of formwork before pouring in fresh concrete. Whereas fibres are evenly distributed directly in fresh concrete during the mixing process. If the efficiency of rebars is mainly dependent on initial calculations and their spatial placement, then the efficiency of fibres is greatly affected by their distribution factor in concrete. As the density of metallic fibres is approximately 3 times higher than that of concrete, the prevention of sedimentation of the metallic fibres during curing is considered a major challenge for the application of such fibres. In our work, we are focusing on obtaining a uniform distribution of high tensile strength metallic microfibers. Self-compacting high-performance concrete with an aggregate diameter of less than 1.25 mm was used as a matrix and high tensile strength metallic fibres with an aspect ratio of 40 were used as reinforcement. Different superplasticizer concentrations were used to modify the rheology of the mix until uniform fibre distribution was obtained, and sedimentation of fibres was prevented.