Experimental investigation on the response of UHP(FR)C at high stress-rates under compression

Understanding the dynamic response of Ultra-High Performance Fibre-Reinforced Concrete has important implications for engineering applications, including protective structures and critical infrastructures. It is wellknown that the loading rate affects both material failure mechanism and mechanical properties such as strengths and absorbed energy. Moreover, materials properties are influenced by stress confinement, which usually occurs in a real structure. The aim of this preliminary experimental campaign was to analyse the behaviour of the dynamic response of UHPFRC and its matrix under compression considering a pre-compression state of 56.5 MPa (about 1/3 of the failure stress). Compression at high stress rate (1.5 TPa/s) were carried out on cylindrical specimens with diameter of 30mm and three different heights of 30, 45 and 60 mm, respectively. An increment of strength and fracture time has been observed while increasing of the length of the specimen and a slight reduction of both quantities with the introduction of fibres for the longer specimens. The experimental results are analysed and discussed with the aim to better understand the mechanical behaviour of UHPFRC materials in case of dynamic event under service loading conditions and to study the size-effect on the material response