3D mesoscale study on the effect of ITZ and aggregate properties on the fracture behaviors of concrete based on discrete element method

The discrete element method (DEM) was utilized to study the effect of the interface transition zone (ITZ) and coarse aggregate properties on the compressive fracture behaviors of concrete at a micromechanical level, in which the ITZ was represented by the contact bond and the coarse aggregate was crushable. The linear parallel bonded model was introduced to represent the constitutive model of concrete, and the meso-scale parameters were determined by laboratory mechanical tests. And then, a series of numerical tests were conducted under compressive loading, and the research objects contain ITZ strength, and aggregate properties (i.e., strength, content, size, and shape). The simulation results show that as the ITZ strength increases, the compressive strength shows a nonlinear increase trend. Moreover, as the aggregate strength and content increase, both compressive strength and strain to damage consequently increase, the aggregate shape is independent of the compressive strength. The increase in the aggregate size can reduce the total surface area of the aggregate, leading to a small compressive strength. The compressive strength appears to increase first and then decrease in trend as aggregate surface roughness increases. In addition, the increase in aggregate strength and content induces the failure pattern changes from local microcrack propagation to global failure. Overall, this work comprehensively evaluates the effect of ITZ and coarse aggregate properties on the damage of concrete at a micromechanical level.