Investigating the pore structure of blended cement with synchrotron microtomography Zusammenfassung: Supplementary cementitious materials (SCMs) such as fly ash and slag are exten sively used as mineral substitutes in cement and concrete production owing to the lower energy consumption and reduced CO2 emission. The pore structure of such cement pastes plays an important role during hydration and ultimately durability.In this work the pore structures of blended cement paste were investigated as a func tion of hydration time and blending types by means of high resolution synchrotron tomography. Image processing algorithms are explored and their suitability for pore structure characterization is evaluated. The extracted data with respect to the pore features (volume surface area equivalent diameter etc.) can then be summarized and described by box plots. Specifically a modified box plot with a plateau indi cating the systematic error is introduced to assess the segmentation precision. The applicability and robustness of this approach is evaluated using different sample sets and experiments. Further durability and mass transport are examined by analysis the total pore volume and the effective connected pore cluster.As a result of this work synchrotron based microtomography is identified as a promising method for the study of pore structure in blended cements. The image processing algorithms are proven to have a low error level and systematic errors in the examined pastes are in the same order as the corresponding stochastic er rors. The results indicate that cement pastes benefit from SCMs in microstructure development. Moreover moist environment has a significant refinement of pore structure. In particular the average pore volume is up to ten times smaller than for conventional sealed cement pastes. A nonparametric approach to the segmentation systematic errors for the pore structure qualification of blended cement pastes is established