Abstract: A random spring model is used to simulate mesoscopic fracture processes in cement-based composites. The 3-D spatial distribution of aggregate inclusions is modeled based on a given grading and gravel content in the composite. The 2-D space of the cement matrix and interfacial zone is divided into small elements using the concept of Voronoi polygons. Both the elements and aggregate inclusions are assumed to be rigid bodies connected by the normal and tangential springs. Numerical results are given for a fracture test of concrete CT specimens and concrete cube specimen under uniaxial compression, and useful information concerning the mesoscopic behavior of the failure process is obtained.