Study on the dynamic fracturing characteristics of aggregate-mortar interface under various loading rates using DIC

The dynamics of fracture characteristics at the aggregate-mortar interface under varying loading rates present a significant area of investigation, pivotal for comprehending the response of concrete to dynamic load conditions. In concrete, the interface between the aggregate and the mortar forms a significant region, fundamentally dictating concrete structures' comprehensive strength and durability. This study aims to investigate the interface crack propagation process, including the crack propagation velocity and the propagation direction using Digital Image Correlation (DIC). Three-point bending beams with a single-size aggregate were fabricated. Beams with different initial crack tip-to-aggregate distances, d0 (aggregate position) of 20 mm, 40 mm, and 60 mm, were tested at five different displacement-loading rates (0.012 mm/min, 0.12 mm/min, 1.2 mm/min, 12 mm/min, and 120 mm/min) using an electro-hydraulic servo testing machine. The crack propagation process was documented utilizing a high-speed video camera. The study reveals a direct correlation between loading rates and concrete's mechanical attributes. The results indicate that as loading rates rise, the compressive strength, tensile strength, and modulus of elasticity of concrete notably increase, while the Poisson's ratio decreases. The initial fracture toughness (Kini Ic ) also escalates with increasing the rates, its sensitivity notably influenced by d0. Concurrently, fracture energy increases with the increase of loading rate and the decrease of d0, a trend more evident at high loading rates. The crack initiation load (Pini) for all single-size aggregate concrete beams was higher than that of plain concrete, and Pini decreased as d0 increased. Observations were made on the trajectory of crack formation, further scrutinizing the effects of d0 and the variable loading rate. Notably, the presence of the interface was found to slow the crack propagation velocity, and this ability to inhibit crack propagation decreased as d0 increased. As the loading rate increased, the crack propagation velocity at the mortar matrix and interface also increased. This study also reports additional material properties, such as critical crack length, and interfacial fracture mode.