Size effect on the dynamic tensile characteristics of concrete subjected to a high loading rate

The influences of loading rate and specimen size on the dynamic tensile behaviour of standard concrete (SC) (grade M35) and high-strength concrete (HSC) (grade M60) were investigated using the split Hopkinson pressure bar apparatus. The dynamic splitting tensile strength of the SC increased from 10.43 MPa to 18.56 MPa as the loading rate was increased from 130.3 GPa/s to 412.3 GPa/s. Similarly, for the HSC, the dynamic splitting tensile strength increased from 12.0 MPa to 19.86 MPa with an increase in loading rate from 214.5 GPa/s to 492.9 GPa/s. The larger specimens, with higher rate sensitivity, showed higher tensile strength and dynamic increase factor (DIF) owing to lateral inertia and crack propagation. The quasi-static size effect law was modified for dynamic loading conditions and the critical stress rates were 59.2 GPa/s for SC and 88.8 GPa/s for HSC. The modified DIF model of CEB-FIP, considering strain rate and size effect simultaneously, strongly supported the experimental DIFs with deviations within ±13%. The splitting tensile strength of SC and HSC calculated using a modified equation for brittle rock materials showed a deviation of ±10% of the experimental values.