Study on the dynamic fracture properties and size effect of concrete based on DIC technology

•The fracture behavior of concrete has obvious size effect and strain rate effect.•The stage of rapid fracture propagation is delayed with the increase of strain rate.•The displacement of crack opening increases with the increase of strain rate. The fracture properties of concrete are highly influenced by the size effect and strain rate effect. To explore the size effect on the dynamic fracture properties of concrete, a fracture experiment on the three-point bending beam was carried out in this paper under four strain rates (10−5/s, 10−4/s, 10−3/s and 10−2/s) and three span to height ratios (2, 2.5 and 3). Then, the fracture characteristic parameters and mechanism were analyzed based on the experimental data combined with the digital image correlation (DIC) technology. The results indicate that the fracture properties of concrete have an obvious strain rate effect and size effect. The fracture load, fracture energy and crack initiation toughness all increase with an increasing strain rate, but decrease with an increasing span to height ratio. On the contrary, the unstable fracture toughness shows no obvious size effect or strain rate effect. Based on the DIC technology, the evolution of crack propagation length in different loading stages was calculated. It is shown that, under the strain rate of 10−5/s, 10−4/s, 10−3/s and 10−2/s, the rapid propagation of crack occurs in the period from Pre-70% to Pre-90%, from Peak load to Post-90%, from Post-90% to Post-80%, and from Post-90% to Post-80%, respectively. More specifically, the crack propagates most rapidly under the strain rate of 10−2/s. The rapid propagation period tends to be delayed with the increase of strain rate, and the strain rate effect is gradually weakened with the increase of span to height ratio. By carrying out in-depth research on the dynamic fracture failure mechanism of concrete, this paper provides reference for the future studies on the dynamic fracture properties of concrete.