This paper develops a mathematical model using mosaic patterns to characterize structural features of complex, multiphase, and multidimensional microstructures, such as those for cement paste. A multiphase microstructure can be characterized by
mindependent parameters; the first m– 1 parameters are equivalent to the volume fractions of the phases, while the final parameter describes the grain size, and thus, the spatial arrangement of the microstructure. An evaluation procedure for the parameters is given; they can be evaluated based on a 2D image, and then the 3D microstructure can be simulated by the present model. The relationship among the model parameters and material parameters, such as water-to-cement ratio and particle size distribution, are also established.