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- Natural pozzolans (2) (entfernen)
Industrial byproducts and natural pozzolanas are increasingly being used as supplementary cementitious materials. In the group of natural pozzolanas volcanic ashes are the most prominent. Despite the fact that volcanic pozzolanas were used since Roman times, not much is known about their role in influencing the long term durability of concrete. The paper presents results of the volcanic pozzolana ‘Rhenish trass’, which is quarried in western Germany and its role during an alkali silica reaction (ASR). Field data and laboratory experiments indicate that trass releases alkalis into the pore solution but also changes cement paste chemistry and alkali binding behavior. There seems to be a sensitive balance between alkali release and increase of alkali binding capacity, both mechanisms crucial for the course of an ASR in concrete.
Many African countries face serious problems associated with the rapid growth of urban Population and the resulting demand for affordable building materials. In search for appropriate Solutions to improve the Situation, the “LightSHIP” project was initiated, whose aims were to identify the required product specifications, to evaluate possible approaches and ultimately to develop new Building materials for East Africa. It was concluded that these materials should be produced in Africa mainiy from local raw materials; prefabricated, easily transportable construction elements are to be preferred. It is therefore reasonable to focus on artificial stones and partition boards. To be Independent of imported cement, it is suggested to make use of volcanic rocks, which are abundant in East African countries, for lime-pozzoian binders and geopolymers in the production of these construction elements. Future research activities should thus concentrate on assessment of the applicability of available volcanic rocks, the influence of their properties on the resulting binders and the design of appropriate binder-reinforcement-filler Systems.