Experimental characterization of concrete in dynamic tension

Tensile tests on cylindrical specimens made of wet and dry concrete have been performed at different strain rates from 10 s−1 to 120 s−1 by means of a special experimental technique. This technique enables obtaining of high strain rates by application of one instrumented Hopkinson bar as a stress wave transmitter into a short specimen in order to trigger a spall failure. The experiments clearly demonstrated a significant increase of tensile strength occurring in the range of strain rates above 10 s−1. The substantial increase of strength as a function of loading rate is confirmed by pictures of the failure process recorded by series of fast CCD cameras (106 pictures/s). The coupled effects of moisture content and strain rate are experimentally investigated and revealed that the water content is not a main influencing factor on strength. On the contrary, analyses of the fracture surfaces performed by optical and scanning microscopy clearly indicated that almost all aggregates were cleaved. Taking into account that observation, and another information on delayed failure, a cumulative failure criterion is applied. Such failure criterion seems to satisfy all experimental data.