Experimental study on direct tensile behaviour of UHPFRC under high strain-rates

An experimental investigation was carried out to characterise the direct tensile behaviour at high strain rate of various UHPFRC mix designs (150, 170 and 210 MPa) with various dosages of fibres. The mechanical characterisation at high strain-rate was performed by means of two split Hopkinson tension bar devices and one Hydro-Pneumatic Machine that are installed at the DynaMat Laboratory of the University of Applied Sciences and Arts of Southern Switzerland in Lugano. The direct tensile tests of different UHPFRCs were performed on cylindrical notched specimens of H/D = 1 with 20 mm and 60 mm in diameter (notch/radius = 0.20) and on dog-bone-shaped specimens. The results highlighted different strain rate sensitivities of the materials. Higher dynamic increase factor was registered for the matrix with special thermal curing respect to those cured as usual. Important increment of strength was obtained for the matrix where sand was partially replaced by Silica Fume. These results are the base for better understanding the dynamic mechanical behaviour that will be obtained by further tests on Ultra High Performance Fibre-Reinforced Concretes (other Ductal (R) mixes). Such data will provide designers better and more relevant properties of these materials useful for designing protective structures. (C) 2019 Elsevier Ltd. All rights reserved.