Experimental and mesoscopic study of dynamic tensile properties of concrete using direct-tension technique

Dynamic tensile properties of concrete play a very important role in the blast-resistant performance of concrete structure. Systematic tests on the tensile properties of normal concrete at high strain rates in the direct-tension way by using an improved Split Hopkinson Tension Bar (SHTB) technique were carried out. Quasi-static directtension test was also conducted for comparison. The obtained dynamic tensile stress-strain curves and tensile fracture energy of normal concrete were compared with the existing test data and formulae. Failure appearance of concrete rapidly loaded by direct stretching was also captured with the high-speed camera. A fine 3D mesoscopic concrete model, in which coarse aggregate with random shapes and sizes was randomly distributed in mortar matrix, was employed to conduct the parametric discussion. Experimental and numerical results reveal that the dynamic increase factor of tensile strength (DIF) obtained by the SHTB test is a little lower than that proposed by CEB that fits basically on the dynamic splitting test data. The tensile fracture energy and tensile strength both show significant strain-rate dependence. It acceleratingly increases with the strain rate exceeding a critical value of 2 s-1. The strength of aggregate has little effect on the tensile properties of concrete. The dynamic direct tensile properties of concrete increase with mortar strength and ITZ strength. Improved empirical formulae on DIF and DIFG that denotes the dynamic increase factor of tensile fracture energy of concrete were established that could be used in a very wide range of application.