An Integrated Particle Kinetics Model (IPKM) to simulate the evolution of cement microstructure during hydration is presented. The advantages of the model are that the space is not divided into discrete pixels, so there is no lower resolution on the size of feature which can be represented and that the kinetics of hydration are an integral part of the microstructure formation. One method to describe the resulting pore structure is as a network of cylindrical tubes. This transformation is analytical, which allows a wide range of pore sizes to be described without resolution limit. From this representation the water permeability can be determined by applying Darcy and Poiseuille laws. The numerical results obtained are compared with experimental data. (c) 2005 RILEM. All rights reserved.