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Sustainable structural engineering follows the basic principle that the energy and resources consumption due to the construction and operation of a structure must be minimized. Relating to concrete structures this principle can be realized by the use of the material in the most efficient way considering its strength and durability within the service life of the structure. Againstthis background the presentpaper outlines methods to assess and reduce the environmental impact of concrete and means to increase itsperformance. The presented concept is applied to the concrete type with the greatest potential in sustainability, i.e. green concrete. Thereby, the basic principles of green concrete mix design are introduced and a systematic study of the influence of the cement content on the fresh and hardened concrete properties as well as on durability parameters is presented. From the results it can be seen, that green concretes possess a very high sustainability and, depending on the attack scenario,even might show acceptable durability characteristics whenthey are subjected to corrosive exposures.

EinführungSeit vielen Jahren nimmt die politisch forcierte Nachhaltigkeitsdebatte auch im Bereich des Bauwesens und speziell im Betonbau einen breiten Raum ein. Den Ausgangspunkt für die Bewertung der Nachhaltigkeit eines Betons bilden dabei die Umwelteinwirkungen, die mit der Betonherstellung einhergehen. Development principles and technical boundaries of concrete production with low cement content This paper explains the principles of proportioning ecologically sustainable, cement reduced concrete mixtures. It attempts to provide an answer to the question of how the cement content in concrete can be reduced without adversely affecting key characteristics, such as consistency and compressive strength. The central element of the proposed algorithm for mixture development consists of particle packing models, with which the water demand of the granular mixture of cement, stone dust and aggregate can be minimized. In this report a combined approach, consisting of the particle size distribution model of Funk and Dinger and the CIPM model of FENNIS, is proposed. The experimental investigations carried out suggest that it is possible to reduce the binder intensity (the demand for binding material to produce 1 MPa of compressive strength in 1 m³ of concrete) of the concrete by a factor of ca. 3 as compared to normal concrete when following this approach. The experimental investigations also suggest that the workability of the mixtures can be estimated well by the quotient function between the actual particle packing density and a theoretical maximum particle packing density of the granular mixture.

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