Effect of loading rate on fracture energy of high-strength concrete

Three-point bending tests on notched beams of a high-strength concrete have been conducted using both a servo-hydraulic machine and a self-designed drop-weight impact device. The fracture energy (G_F) was measured over a wide range of loading rates, spanning eight orders of magnitude. Under low displacement rates, from 10^-4 mm/s to 10 mm/s, the tests were performed with the servo-hydraulic machine; from 10² mm/s to 10³ mm/s the drop-weight impact machine was used instead. The results show that the fracture energy increases as the loading rate increases. Nevertheless, such a trend is relatively mild under low rates and can be attributed to viscous effects mainly originating from the presence of water in the pore structure. Under high rates the increases in the fracture energy is dramatic due to the effect of inertia.