Experimental investigation of crack propagation and crack branching in lightly reinforced concrete beams using digital image correlation

Relatively few fracture-oriented experimental studies have been conducted on concrete that is reinforced. An experimental investigation was therefore undertaken to explore the cracking process in lightly reinforced concrete (RC) beams and to observe the details of the localised fracture process zone development. More specifically, the aims were to investigate the relationships between beam height (120 mm, 220 mm and 320 mm), steel reinforcement ratio (0.1-0.5%), ductility and the onset of crack branching. RC beams were tested in three-point bending and experimental surface strains and crack openings were inferred using digital image correlation (DIC). It was found that the presence of the reinforcement prevented premature fracture and led to crack branching where a single crack bifurcated in the region of the compression zone. In the larger beams the branching developed at a lower relative height and a greater reinforcement ratio led to a shallower branching angle. These observations were associated with ductility measures for lightly reinforced concrete beams.