The mechanical properties of both ordinary concrete and less binder concrete are examined in terms of uni-axial compression, shear and cyclic compression under tri-axial condition. The uni-axial compressive strength decreased with decrease of mortar volume. Decrease of shear resistance was not proportional to decrease of mortar. However, cohension with assumption of 35degree of internal friction was clearly affected by mortar volume. The strain distribution suggested that fracture of concrete started from upper to lower. Mohr's circles of the materials on the way to segmentation implied that the mechanical properties of both concrete and gravels can be estimated with single method. According to these experimental facts, the mechanism of segmentation of bridge deck was described.