Projectile Impact Resistance of UHPFRC Structures for Various Methods of Fresh Mixture Placement

This paper present results of an experimental investigation of the projectile impact resistance of ultra-high-performance fibre-reinforced concrete (UHPFRC) slabs. The paper also investigates transparent viscous liquid, based on the ultrasound gel, as an effective suitable tool to replace fresh mixture of ultra-high-performance concrete. The description of the viscous behaviour of both materials and optimisation of the ultrasound gel is shown. An arrangement of fibres in the UHPFRC mixture was demonstrated by the ultrasound gel with an addition of steel fibres. The influence of horizontal and vertical casting of thin slabs against penetration by a projectile was tested and described. The resistance to the penetration was investigated using full-metal jacket projectile with soft-lead core. The results indicated various penetration depths and crater diameters in the target specimens for both methods of casting. Various methods of casting resulted in various arrangement of fibres for both horizontally and vertically casted slabs. However, the protective capacity was guaranteed for both placement methods. The desired outcome was determination of the UHPFRC mechanical properties and projectile impact resistance, depending on the orientation of fibres which depended on the method of placement of the fresh mixture into the formwork. The direction of mixture placement into the formworks had a significant impact on achieved mechanical properties of the hardened concrete. Based on the present findings it was found that slabs from ultra-high-performance fibre-reinforced concrete casted horizontally appear to be more efficient in protection against projectile impact.