The results of the physical characterization of the C-LWA pellets are presented in Table . No statistically significant differences were found between the three size fractions (8-12, 12-16 and 16-20 mm), hence the results presented in Table were averaged. The microstructure of the C-LWA embedded in concretes studied with X-ray tomography is presented in Fig. . Larger pieces of the original biochar, with their characteristic layered structure (see also ) can be identified within the pellets. The darker colour of the pellets compared to the surrounding cement paste and aggregates is due to their high porosity (stemming from the original high content of water) and fine biochar particles that are below the resolution, whereas the light-coloured regions correspond to higher density.