Damage evolution of concrete under tensile load using discrete element modeling

The objective of this study is to investigate the damage evolution process in the flattened Brazilian test of concrete, and assess the effect of the maximum aggregate size on the tensile strength of concrete using the discrete element method considering the heterogeneity of concrete. Random irregular coarse aggregates were generated in each gradation according to the theoretical content. Based on this, a series of discrete element numerical models of flattened Brazilian disks with aggregates of different gradations were established, including 5–10, 5–16, and 5–20 mm, and numerical simulations of flattened Brazilian tests were conducted. Before the peak load, the compressive force was concentrated near the flat loading ends, which can be considered as the driving force for the initiation of shear microcracks, and the tensile force distributed away from the loading ends induced the appearance of tensile microcracks in the mortar and the interface transition zones (ITZs). Tortuous macroscopic cracks formed owing to the accumulation of tensile microcracks at the center of the specimen when the peak load was reached. After the peak load, secondary cracks initiated and extended gradually, and shear failure began to occur in the mortar and the ITZs owing to the redistribution of the compressive force. The failure mechanism was correlated with the displacement trends of the particles. Tensile microcracks could be associated with the tensile displacement trend of the particles. Shear and tensile microcracks co-existed in the zones where the particles moved in a mixed-mode displacement trend. The tensile strength of the concrete decreased slightly with an increase in the maximum aggregate size in the flattened Brazilian tests, and the tensile strength of the concrete was overestimated by the flattened Brazilian tests.