Experimental Techniques to Characterize the Mechanical Behaviour of Ultra-High-Strength-Concrete Under Extreme Loading Conditions

In the present work, three experimental methods have been employed to characterize the dynamic tensile, shear and confined behavior of an UHSC (Ultra-High Strength Concrete) with and without steel fiber reinforcement. On the one hand, a dynamic testing method was developed to investigate the post-peak tensile behavior of UHSC. A Split-Hopkinson Pressure Bar (SHPB) device is used and the notched-concrete sample is glued in-between the input and output bar. A compressive pulse reflects as a tensile pulse leading to the breakage of the sample. In this case a strong influence of fibers is noted. On the other hand, two experimental methods are used to investigate the confined behavior of UHSC under shear and quasi-oedometric loading paths. In the quasi-oedometric compression test the concrete sample is inserted in a confining vessel and axially compressed. Hydrostatic pressure as high as 800 MPa are obtained and the hydrostatic and deviatoric behavior are deduced. The PTS (Punch-Trough-Shear test) provides lateral pressure of over 70 MPa in the sheared zone, high shear strain and leads to a mode II fracturing of the sample. Influence of fibers on the dynamic behavior of UHSC is discussed thanks to the previous experiments.