Experimental Investigation of Crack Propagation and Branching in Lightly Reinforced Concrete Beams

The main aim of this project is to investigate the nature of fracture in reinforced concrete. An experimental investigation was therefore undertaken to explore the cracking process in lightly reinforced concrete (RC) beams and to observe the details of the localized fracture process zone development. More specifically, the aim was to observe the effect of beam depth (150 mm and 180 mm) and steel reinforcement ratio (0.3–0.6%) on ductility through the investigation of crack branching. A total of six beams were cast in two series of two sizes (depths of 150 and 180 mm and lengths of 1000mm and 1200 mm respectively) keeping the width same (100 mm) for all the beams. Each of the series includes one unreinforced and two reinforced beams. All the six beams were tested in three-point bending and experimental surface strains and crack openings were inferred using high resolution digital camera and crack microscope. 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 (of depth 180mm and length 1200 mm) the branching developed at a lower relative depth and a greater reinforcement ratio led to a wider branching angle. These observations were associated with ductility measures for lightly reinforced concrete beams.