Strain rate and size effects on dynamic tensile behaviour of standard and high-strength concrete: An experimental study

Abstract

The strain rate and specimen size are the main dominant factors affecting the splitting tensile behaviour of concrete. The static size effect is well-known for concrete behaviour, but it needs more knowledge about the dynamic size effect. The present study investigated the strain rate sensitivity and size effect dependency of dynamic tensile behaviour of two different grades of concretes (M35 and M60) using the Split Hopkinson Pressure Bar (SHPB) setup. From the outcomes of the experimental analysis, it was noted that the quasi-static tensile strength underwent a reduction of 8.96% and 11.39% in standard and high-strength concrete, respectively. This decrease occurred as the diameter increased from 29.5 mm to 45 mm, aligning notably with the principles outlined in the "Bazant Size Effect Law," as proposed by Bazant et al. [52]. Whereas, the dynamic tensile strength and DIF increased with increased specimen diameter, which is opposite to the quasi-static size effect. The maximum split tensile strength observed was 18.56 and 19.86 MPa, corresponding to 13.30 and 12.13 s−1 strain rates with 3.69 and 3.51 dynamic increase factor (DIF) for standard (M35) and high-strength concrete (M60), respectively. The dynamic results also demonstrated a size-effect dependency, where larger diameter specimens exhibited higher strain rate sensitivity, leading to increased strength and DIF due to lateral inertial and crack propagation effects. The modified DIF model of CEB-FIP proposed by the Malvar et al. [17] considering the strain rate and size effect simultaneously strongly supported the experimentally obtained DIF values with an ± 13% deviations. In addition, the strain rate significantly influenced the concrete failure pattern, but no size effect was observed. At a low strain rate, the initiated crack propagated towards the loading ends and split the specimen into two semi-cylindrical halves with penetration cracks. While at higher strain rates, additional wedge-shaped crushed regions formed at the loading end due to tensile and shear damage generated due to stress concentration and local crushing. The crack width becomes wider, and the triangular-shaped local crushing zone continuously moves toward the centre of the specimen from both loading ends and generates the crushed strap.