Effect of the type of coarse aggregate on structure and properties of ultra-high strength concrete

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The production of ultra-high strength concrete requires high-strength aggregates. Basalt and quartzite or quartz sand are commonly used. Nevertheless, there are many other rock types that may be usable. With some of these types, chemical reactions at the aggregate-binder interface are to be expected, resulting in a very strong adhesion. At the same time there are only very few investigations on the influence of different rock types on the mechanical behaviour of ultra-high strength concrete and no investigations in which the reasons for the different behaviour were examined. Exactly this is the aim of the research project. Therefore reliable data on the influence of the rock type on compressive strength, the stress-strain curve under compression, the tensile strength in bending and the behaviour under shock will be measured. The reasons for the observed differences will be analyzed by investigating the aggregate and especially the aggregate-binder interface by high-resolution analytic methods. In particular, transmission electron microscopy will be used in combination with focused ion beam methods of sample preparation. In contrast to scanning electron microscopy, transmission electron microscopy has a resolution in the nanometer range even if used for chemical analysis. The research project therefore generates an important basis for a more sustainable and economic application of ultra-high strength concrete, with a broader range of basic materials and a scientific understanding of the effects of different rock types. The importance of ultra-high strength concrete will clearly grow by the foreseeable establishment of rules for this building material, also in Germany.