The effects of specimen size and aggregate on the evolution of the fracture process zone in concrete: A mesoscale investigation

As a multi-phase composite material, the specimen size and aggregate characteristics (distribution, contents and sizes) of concrete have significant effects on the evolution of the fracture process zone (FPZ). In this paper, mesoscale fracture simulations are conducted using an approach coupling the scaled boundary finite element method (SBFEM), unified phase-field model (PFM) and cohesive interface elements (CIEs). The focus is on studying the effects of meso-structures on the evolution characteristics of the FPZ. The non-cracked regions are modelled by the SBFEM polygons. The damage of mortar and interfaces is simulated by the unified PFM and CIEs, respectively. Concrete three-point bending tests are first simulated to demonstrate the effectiveness of the developed model in depicting the evolution of the FPZ. Further parameter studies on aggregate characteristics are carried out. The results shown that the aggregate content has a significant impact on the FPZ evolution compared to the aggregate size in the post-peak stage. The length of the FPZ is highly dependent on the specimen size, whereas the width of the FPZ shows lower sensitivity to size. These discovered are beneficial for understanding the relationship between the macroscopic performance and mesoscale properties of concrete.