Fracture Toughness of Rocks

The fracture toughness KIC of interfaces between rocks consisting of gypsum rock and concrete was investigated. The cylindrical specimens had a diameter of 40 mm and a length of 150 mm with a V-shaped cut in the middle part. They consisted of two halves - gypsum rock and sand-cement mortar with a rock-concrete interface. Deformation of the specimens under bending according to the three-point scheme made it possible to determine the KIC based on the maximum force at 5-6 cycles. The average KIC value between rock and concrete was much lower than for rock and even for specimens made entirely of concrete. The formation of a calibrated crack during testing leads to a relative increase in the internal mechanical loss coefficient Q–1, determined by the resonance method, up to 30%. The study was supported by the Russian Science Foundation grant No. 24-27-00103, https://rscf.ru/project/24-27-00103/