Study on shear transfer performance of modeled natural aggregate concrete

This study investigates the shear failure behavior of modeled natural aggregate concrete (MNAC) through direct shear tests, with particle size (17, 23, and 30 mm) and aggregate quantity (1, 2, and 3) as key variables. In the course of testing, three distinct shear failure modes were identified: aggregate fracture (Type I), aggregate external envelope fracture (Type II), and interfacial transition zone (ITZ) failure (Type III). Specifically, Type I failure mode occurred only in specimens with a smaller quantity and particle size (MNA17-1 and MNA23-1), whereas the other specimens exhibited Type II, Type III, or a combination of Type II and Type III failure modes. Notably, both larger particle size and aggregate quantity enhanced shear capacity. For example, in single-aggregate specimens, increasing the particle size from 17 to 30 mm raised the pre-cracking peak strength (P₁) and post-cracking secondary peak strength (P₂) by 42.3% and 43.2%, respectively. Similarly, for specimens with a particle size of 17 mm, raising the quantity from 1 to 3 increased P₁ by 35.9% and P₂ by 93.2%. Collectively, these results clarify the role of mesoscale aggregate characteristics in governing macro-scale shear mechanisms, providing new insights into the shear resistance of concrete.