Experimental results indicate that propagation paths of cracks in conc
rete are often irregular, producing rough fracture surfaces which are
fractal. Based on dynamic analysis of microcrack coalescence, this pap
er presents a statistical fractal model to describe the damage evoluti
on of concrete. The model demonstrates that the mechanism of fracture
surfaces formed in concrete is closely related to the dynamic processe
s of the cascade coalescence of microcracks. A unimodal relation betwe
en the fractal dimension and the coalescence threshold can qualitative
ly explain the relation between fractal dimension and fracture energy.