This paper presents the results of several investigations concerning special durability aspects of mortar and concrete with higher proportion of calcined clays in the cement part.For this purpose, different clays based on kaolinite, montmorillonite and illite were fired at optimum temperatures according to the strength contribution in cement.The raw materials were analyzed chemically (XRF) and mineralogically (XRD).The pore size distributions of mortars were measured by mercury intrusion porosimetry.Cement pastes were produced in order to calculate the phase composition by XRD/Rietveld and to estimate the microstructure with SEM.The performance tests comprised investigations of the long-term behaviour in case of sulphate attack and alkali silica reaction, respectively.The results show that all calcined clays are active pozzolans in terms of strength contribution but perform different with regard to the concrete durability.Whereas metakaolin blended cements prevent the concrete to be damaged under all tested conditions, beneficial effects of the other calcined clays are only noticeable in case of the ASR containment.Consequently, the suitability of these materials for special durability problems is strongly limited and their application in concrete, if not otherwise proven by performance tests, has to be restricted to moderate environments.