An imitating model of concrete is proposed in the form of a two-component system consisting of a matrix and inclusions - porous aggregate grains simulated by convex polygons. On their border, there is a zone of contact with properties other than the matrix and inclusions, and in the bulk of the material (in the matrix and inclusions), initial defects of the pore structure of various shapes and sizes are randomly located. Unlike concrete on porous aggregates in heavy concrete, the defectiveness of the macrostructure is due to the violation of the contact of granite rubble with the matrix.