Study on crack propagation behaviors of three-point bending concrete beams with small span-depth ratios

Three-point bending (TPB) beams with small span-depth ratios, i.e. TPB beams with the same span of 400 mm but various depths (100 mm, 150 mm and 200 mm), were tested to study the crack propagation behaviors of concrete. The evaluations of crack extension resistance curve (K_R-curve), fracture process zone (FPZ) length, l_FPZ, and crack tip opening displacement (CTOD) were studied. The digital image correlation (DIC) technique was utilized to monitor the entire loading process. Moreover, the effects of strain rates (10⁻⁵/s, 10⁻⁴/s, 10⁻³/s and 10⁻²/s) on the fracture process of TPB beams with small span-depth ratios (2, 2.5 and 3) were discussed based on findings in literature. The results shown that (1) with the increase of specimen depth from 100 mm to 200 mm, the obtained K_R-curves and initial fracture toughness were not influenced by the small span-depth ratios, while different increase trends were observed for the unstable fracture toughness, the average maximum value of l_FPZ and the value of CTOD. (2) With the loading rate increasing from 10⁻⁵/s to 10⁻²/s, the obtained K_R-curve and the maximum length of FPZ increased slightly, while the evolution of CTOD was not affected by the loading rate.