Towards Rebar Substitution by Fibres – Tailored Supercritical Fibre Contents

Structural application of steel fibre reinforced concrete (SFRC) progressively increases. To create load-bearing components without additional steel reinforcement, mixtures with supercritical fibre contents tailored to the structure and application must be devised. An innovative formwork concept is developed that enables for fibre contents up to 1.0 Vol.-% the steered alignment of fibres. Based on the observation that fibres orient parallel to formwork edges it applies internal formworks. The efficiency is verified by measurements of spatial fibre orientations and flexural tensile strengths. Results on single span beams indicate that favourable fibre orientations perpendicular to cracks can be achieved which is even more effectively with increasing fibre content. The impact does not go along with enhancements of flexural tensile strength. To investigate the effect of steered fibres on bearing capacities of spatial elements like slabs, the SFRC’s composition is optimized with regard to fibres’ content and orientation. The aim is to achieve two-dimensional fibre orientations in directions of principle tensile stresses by artificially limiting the specimen’s height, so that fibres align horizontally in concrete’s flow direction without additional steering. For a supercritical fibre content of 1.8 Vol.-%, it is possible to substitute conventional (mesh) reinforcements of approximate 6.7 cm²/m (f_yk = 500 N/mm²).