Effect of Aggregate Size on the Fracture Behavior of Concrete Under Modes I, III, and I/III Conditions

In this paper, the effects of aggregate size and its corresponding appropriate specimen size on the fracture behavior of concrete under pure mode I, pure mode III, and mixed mode I/III are examined experimentally. The innovation of the present study lies in the use of edge notched disc bend (ENDB) specimens with sizes appropriately scaled to a wide range of aggregate gradations, from mortar to coarse-grained concrete, allowing for meaningful assessment of fracture behavior under mixed-mode I/III conditions. The outcomes provide new insights into the effects of aggregate size on fracture toughness, crack propagation, and applicability of various fracture criteria. It was revealed that aggregate size has a substantial impact on crack propagation behavior under diverse loading conditions. By clarifying the distinction between aggregate volume fraction and maximum aggregate size, we found that fracture toughness generally increases with aggregate size. Larger aggregates contribute to enhanced fracture resistance by promoting greater energy dissipation and facilitating crack bridging mechanisms. Moreover, the experimental results are predicted using several three-dimensional fracture criteria. It is shown that strain-based fracture models exhibit better performance in forecasting fracture behavior in the samples containing larger aggregates than their energy-based and stress-based counterparts.