Effect of tensile strength of rock on tensile fracture toughness using experimental test and PFC2D simulation

The effect of tensile strength on the tensile fracture toughness of rock like specimen was studied in this paper. Brazilian test was done to determine tensile strength of material. A compression to tensile load transforming (CTT) device was developed for determination of mode I fracture toughness of concrete. Also particle flow code (PFC) was used for validation of the experimental outputs. Three concrete slabs with different tensile strength were prepared for investigation of the effects of tensile strength on the fracture toughness. The samples were made from a mixture of water, fine sand and cement with different ratio. These samples were installed in CTT device. A 30-tons hydraulic load cell applied compressive loading to CTT end plates with a constant pressure of 0.02 MPa per second. Compressive loading was converted to tensile stress on the sample because of the overall test design. The results show Fracture toughness has a close relationship with tensile strength of concrete so it increases with increasing the tensile strength. In constant join length, the angle of crack growth related to normal load was decreased with increasing the grain size. Numerical simulation shows that failure pattern and fracture toughness was nearly similar to experimental results. Finally, it can be concluded that CTT device was capable for determination of fracture toughness of concrete.