The effect of bedding planes on the bending strength of rock-like material and evaluation of the crack propagation mechanism

Bedding planes affects various material properties, including the bending strength and the crack propagation mechanism of rocks. In this paper, laboratory studies on rock-like material specimens were conducted to investigate the effect of bedding planes on the failure and crack propagation mechanism and to reduce the effect of secondary factors on the results. To this end, semi-circular bend (SCB) specimens were prepared with two concrete mixing designs using aggregate and geopolymer concretes as materials. Next, they were subjected to compressive and three-point bending tests. The crack propagation mechanism, changes in the bending strength, maximum fracture load, relative midspan displacement, fracture energy, and fracture toughness were analyzed for the anisotropic and isotropic specimens. Also, different bedding angles were examined for the anisotropic specimens. The results revealed that bedding planes generally affected the crack propagation mechanism and changed the fracture mode from pure opening mode for the isotropic specimens to mixed modes for different bedding angles. Hence, the strength and fracture parameters were generally smaller in the anisotropic specimens than in the isotropic ones. With an increase in the bedding angle in the specimens, the maximum fracture load and the fracture surface energy increased, and the midspan displacement behaved differently. Moreover, the fracture toughness displayed an increasing trend with increasing the bedding angle in the anisotropic specimens. The rate of changes in the parameters were different for different bedding angles. This may be attributed to the changes in the stress distribution and to the fracture and crack propagation modes in the anisotropic specimens compared to the isotropic ones.