Improvement of UHPFRC-Rheology by Using Circular Shape Memory Alloy Fibres

Abstract

Fibre reinforcement of Ultra-High Performance Concrete (UHPC) is linked to a reduction of the flowability of fresh concrete. Moreover, high fibre contents often promote agglomerations. Therefore, commonly a fibre content of about 1–2 vol.-% is used. A novel method is proposed to minimise the negative influence of high fibre contents on the rheological properties of fresh concrete without any significant deterioration of the mechanical properties of the hardened concrete. To achieve this, shape memory alloy (SMA) fibres made from nickel and titanium are proposed to be used. These SMA-fibres have the ability to transform into an imprinted geometry upon heating. During mixing, fibres with a circular geometry avoiding agglomerations are added and, therefore, the rheological properties of fresh concrete can be improved compared to straight fibre reinforced concrete. After mixing the UHPC, the shape memory effect is thermally activated while the concrete is still flowable. The fibres transform into their imprinted, straight geometry enhancing the properties of the hardened concrete. With this method we propose to combine the improved mechanical properties of a fibre reinforced UHPC with a good workability. The present work presents a first step towards achieving the final goals.