Aside from porosity, the degree of pore connectivity and tortuosity are important pore structure characteristics of cement-based materials to understand better the effect of microstructure on transport processes that influence the durability of these materials. Synchrotron X-ray computed microtomography is employed to provide information about the three-dimensional (3D) pore structure at submicron resolution (0.5 μm/voxel) using the SPring-8 facility in Hyogo, Japan. This paper presents a method to characterize the pore space of hardened cement pastes taken from different specimens of various ages (2, 7, and 28 days) of curing. By defining the pore threshold value on the basis of the transition point in the porosity-threshold dependency curve, the pores were distinguished from the solid matrix in the microtomographic images. Further, pore cluster multiple labeling was performed to gain information on the pore connectivity and the associated effective porosity. 3D random walk simulation in the largest percolating pore cluster was then conducted to evaluate the diffusion tortuosity. The results from this study provide indications of increasing diffusion tortuosity as pores that can be resolved by the X-ray imaging system decreased and became more disconnected. Sensitivity analysis to pore threshold value was performed to evaluate the robustness of the method.
2008 by Japan Concrete Institute