Investigation on crack propagation perpendicular to mortar–rock interface: experimental and numerical

The initiation and propagation of cracks perpendicular to mortar–aggregate interfaces have a significant influence on the mechanical behaviour of concrete materials. Although existing studies have revealed that a perpendicular crack to the interface can penetrate into the aggregate for high strength concrete owing to the stronger interfacial bond strength, the crack propagation penetrating into aggregates has not been fully understood. In this paper, a crack propagation criterion based on the stress intensity factor (SIF) is developed for layered mortar–rock beams with a crack normal to the interface. Based on this criterion, a numerical method is proposed to predict the crack propagation process of layered mortar–rock beams under mode I fracture. After the validity of the numerical method is verified with experimental data obtained in this paper, the effects of the fracture parameters on the crack propagation characteristics in layered mortar–rock beams are evaluated. The results show that the crack propagation behaviour is greatly affected by the difference of the initial fracture toughness and the tension-softening constitutive law between the two materials. If a crack approaches a material with a larger initial fracture toughness, the load increases suddenly when the crack passes through the interface due to the higher resistance against crack penetration. Conversely, when the crack approaches a material with a smaller initial fracture toughness, it rapidly penetrates into the material after reaching the interface, resulting in an obvious discontinuity in the load response. It is also shown that, when a crack grows across the interface and propagates inside a material with a smaller critical crack opening displacement, the cohesive stress distributes discontinuously along the ligament where a traction-free crack is formed in the vicinity of the interface. This paper concludes that the proposed numerical method is effective in predicting the crack propagation process of layered composite beams with a crack normal to the interface.