A TESTING TECHNIQUE OF CONFINED COMPRESSION FOR CONCRETE AT HIGH RATES OF STRAIN

In order to characterise the behaviour of concrete under high pressures and high strain-rates, dynamic 1D-strain compression tests were performed. A cylindrical specimen is embedded in a steel confinement ring and compressed between 2 cylindrical plugs with a SHPB (Split Hopkinson Pressure Bars) device. Moreover, a new method was used to process the experimental data. It is based on numerical simulations of the cell loaded by an internal pressure that allow to build a relation between the pressure applied by the concrete to the inner surface of the cell and the external hoop strain measured by gauges. Stresses and strains in the specimen are computed at any loading time and the evolution of the deviatoric stress versus the pressure (deviatoric behaviour) and of the pressure versus volumetric strain (spherical behaviour) is deduced. The method is validated by several numerical simulations of the test involving different friction coefficients between the cell and the specimen. Three 1D-strain compression tests were performed and processed with the MB50 high-performance concrete. They showed that the deviatoric and spherical behaviours are almost independent of the strain rate in the observed range of strain rates (80-221 s-1). The deviatoric strength is seen to increase regularly with the hydrostatic pressure. The spherical behaviour indicates a fairly constant dynamic modulus of compressibility (around 5 to 6 GPa) up to a pressure of 900 MPa