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High performance fiber reinforced concrete is developing quickly to a modern structural material with a high potential. As for instance testified by the recent symposium on HPFRC in Kassel, Germany (April 2008) the number of structural applications increases. At this moment studies are carried out with the aim to come to an international recommendation for the design of structures with HPFRC. Research projects are being carried out in order to supply missing information in relevant areas. Some examples of recent research at TU Delft are given. For the preparation of an internationally acceptable design recommendation for HPFRC a number of principles should be respected. The code should as much as possible be in harmony with the code for conventional fiber concrete. Moreover it should be consistent with existing design recommendations for structural concrete. Second thoughts on the introduction of such a new code are given.

The aim of the project is to develop computer programs based on the finite element method which are able to analyse arbitrary plane structures of reinforced or prestressed concrete with any type of loading untill failure. Besides all, the shear behaviour of structures should receive the main attention.

Reasons for size dependence of rotation capacity of plastic hinges are discussed. The increase of ductility with decreasing member size is interpreted from the viewpoint of fracture mechanics of concrete. The results of the introductory test series on simply supported slender beams loaded in three-point bending are discussed. A new model for the calculation of the rotation capacity is described, which takes into consideration the strain localisation in the damage zones in the hinge region. In particular, the way of implementing the Fictitious Crack Model, the Compressive Damage Zone Model and a new fracture mechanics based bond model that takes into account the steel stress level (e.g. the yielding of reinforcement) is explained. The results of parameter studies on size effects in plastic hinges are described. Special attention is given to the influence of reinforcement arrangement and of the flexural crack pattern. In conclusions the importance of the size effect in practical design situations is examined and the need for altering the existing design rules in the light of the possible member size dependence of the rotation capacity of plastic hinges is evaluated

The development of self-compacting concrete (SCC) was an important step towards efficiency at building sites, rationally producing prefabricated concrete elements, better working conditions and improved quality and appearance of concrete structures. By adding fibres to SCC bar reinforcement can be replaced and the performance of concrete structures enhanced. Self-compacting fibre reinforced concrete (SCFRC) combines the benefits of SCC in the fresh state and an enhanced performance of fibre reinforced concrete in the hardened state. With the special characteristics of SCFRC new fields of application can be explored. This paper describes results of a PhD-study [Grünewald, 2004], which was carried out at the Delft University of Technology. The effect of steel fibres on the characteristics of SCC in the fresh and the hardened state are discussed. Tools are provided to optimise SCFRC and full-scale case-studies demonstrate the potential of SCFRC.

The project 'self-compacting fibre-reinforced concrete (SCFRC)' is part of the Dutch STW/PPM program - 'cement-bonded materials' - DCT.4010. Subproject III to which the project ,SCFRC' belongs deals with the development of new high performance concretes. The project 'SCFRC' aims at investigating the effect of type and content of fibres on the characteristics of self-compacting concrete in order to optimise the mixture composition. Fibres are able to bridge cracks and to improve the ductility of otherwise brittle cementitious materials. Therefore, the addition of fibres might extend the possible fields of application of self-compacting concrete. Besides the properties in the fresh state, while the concrete still flows, the mechanical behaviour will be investigated. This paper aims at introducing the reader to the goals, methods of research, and first experimental results of the project 'SCFRC'.

Hybrid fiber reinforcement can be very efficient for improving the tensile response of the composite. In such materials, fibers of different geometries can act as bridging mechanisms over cracks of different widths. The fiber bridging efficiency depends on the interface properties, which makes interface characterization very important. Therefore, single-fiber pullout tests from conventional matrices as well as from the fiber reinforced mortar matrices are performed. The composition of the mortar matrix has been varied as well. The pullout response of single fibers generally improves with increasing percentage of fibers in the mortar. Moreover, pullout forces are generally higher when the matrix has a higher strength. In all these cases, intensive microcracking of the surrounding matrix can be observed during fiber pullout. Together with single-fiber pullout tests, standard compression tests and splitting tensile tests, as well as workability studies have been performed, in order to provide experimental data for further research of the high-performance hybrid fiber reinforced concrete.

Self-Compacting Concrete is a relatively new type of concrete. Up to now only a few models have been developed to explain its physical behaviour, like the Water Layer Model and the Excess Paste Model. In this paper, the difference between the Water Layer Model and the Excess Paste Model is highlighted, and the validity of the Water Layer Model to Self-Compacting Mortar with different characteristics of the sand is investigated. The results of this investigation show that the Water Layer Model is effective for the determination of the quantity of water. Furthermore the function of water and superplasticizer is explained using this model.

Hybrid fiber reinforcement can be very efficient for improving the tensile response of the composite. In such materials, fibers of different geometries can act as bridging mechanisms over cracks of different widths. The fiber bridging efficiency depends on the interface properties, which makes interface characterization very important. Therefore, single-fiber pullout tests from conventional matrices as well as from the fiber reinforced mortar matrices are performed. The composition of the mortar matrix has been varied as well. The pullout response of single fibers generally improves with increasing percentage of fibers in the mortar. Moreover, pullout forces are generally higher when the matrix has a higher strength. In all these cases, intensive microcracking of the surrounding matrix can be observed during fiber pullout. Together with single-fiber pullout tests, standard compression tests and splitting tensile tests, as well as workability studies have been performed, in order to provide experimental data for further research of the high-performance hybrid fiber reinforced concrete.