It is shown that the fracture of concrete behaved complicatedly and irregularly, which underwent explicitly a subcritical crack growth prior to the unstablecrackpropagation.
结果表明：混凝土断裂是一个复杂的不规则过程，存在明显的亚临界扩展现象。
2
Coarsening grain and intercrystalline network ferrite depress crack growth resistance of the materials strongly and result in unstablepropagation of crack very easily.
晶粒粗大及晶间网状铁素体强烈降低材料的裂纹扩展阻力，并极易导致裂纹的失稳扩展。
3
It was observed on unstable rib that the crackpropagation mechanisms in both mist and rib regions may transfer into each other.