Sensitivity of the test conditions for direct assessment of dynamic shear properties of fibre-reinforced cementitious composites (FRCC) with Split-Hopkinson bar

Fibre-reinforced cement-based composites (FRCCs) possess pronounced toughness due to the crack-bridging effect of the fibres and represent effective solutions for protecting concrete members against extreme events. In the scenario of localised impacts, protective FRCC overlays are subjected to severe punching shear, for which careful design is required. However, the dynamic shear characterisation of FRCC is complex due to the interplay of different phases in the composite (i.e. cementitious matrix, fibres, and their interaction), and standardised test methods for dynamic shear have yet to be developed. This paper focuses on the dynamic shear characterisation of a high-toughness FRCC based on a fine-grained cementitious matrix containing synthetic fibres. The emphasis is on the sensitivity of the material properties to three different test methods based on the Split-Hopkinson bar approach. Two Split-Hopkinson Tension Bar (SHTB) systems with different load wave generation principles (i.e. gravity versus pretensioned bar) and the same shear adapter for applying pure shear loading are considered. A third setup based on a Split Hopkinson Pressure Bar (SHPB) with coaxial specimens and a punch-through-shear configuration is considered as a benchmark. The results show that, when the same strain rate is applied, the confinement of the sample plays the key role in the determination of the shear properties of FRCCs, while different wave forms coming from different loading schemes are less influential. The sensitivity of the material response as a function of the specimen boundary condition emerged from this study highlights the need for consistent test protocols tailored on the intended application.