Effect of steel–PET fibre reinforcement on the fire resistance of reactive powder concrete

Ultra-high-performance concrete (UHPC) reinforced with hybrid fibres is a novel material with exceptional properties. Steel fibre (SF) provides UHPC with strength, while synthetic fibre leads to other useful properties such as increased fire resistance. In this study, the not so often used combination of SF and eco-friendly recycled polyethylene terephthalate fibre (PETF) was used, with the aim of improving the fire resistance of UHPC. The fabrication process, which involved the use of a vacuum, is also rarely used. The slump flow and mechanical properties of reference UHPC and UHPC reinforced with the hybrid fibres were determined. The fire resistance of these two mixtures was then determined. The effect of the PETF in increasing the fire resistance was studied using backscattered scanning electron microscopy. It was found out that the addition of 0.125 vol.% of fibre was beneficial in terms of preventing explosive spalling while having statistically negligible impact on mechanical properties.