In this study, the transport properties of tritiated water (HTO) and Cl-36 in two different concretes were investigated. The spatial distribution of porosity and radionuclide retention within the studied materials were studied via C-14-Polymethylmethacrylate (C-14-PMMA) autoradiography and Cl-36 autoradiography, respectively. Diffusion experiments and modelling methods were used to calculate the effective diffusion coefficients and distribution coefficients of the tracers. The diffusivities of HTO and Cl-36 were considerably lower in mixed cement (CEMV)-based concrete than in Portland cement (CEMI)-based concrete. Autoradiography-based Cl-36 post-mortem examination revealed important distinctions explaining the diffusion behaviour between the two concrete materials. While there was considerable retention in both, in CEMV-based concrete, the diffusion was considerably slower than in CEMI-based concrete. Overall, the post-mortem autoradiographic imaging was successful, and a similar approach is probably applicable to other radionuclides.