The development of cohesionless cracks can be regarded as a sign of macroscopic crack development. An identification model of cohesionless cracks was adpoted with results of crack development by digital image correlation (DIC) method. Three-point bending tests were carried out on fully-graded concrete specimens with different loading rates (0.0001 mm/s, 0.0010 mm/s, 0.0100 mm/s), considering the rate correlation of crack propagation of fully-graded concrete. The results show that for the fully-graded concrete specimens with different loading time intervals, cohesionless cracks will occur throughout the peak load, indicating that the prefabricated cracks have cracked when the peak load is reached. The cracks of the specimen is mainly concentrated after the load is loaded to 50% of the peak load. Under the same conditions, the slower the loading rate is, the earlier the unbonded cracks appear. With the increase of the loading rate, the cracks are thin and long.