Fibre Orientation and Computed Tomography
For the investigation of a correlation between the experimental results and the fibre distribution, some of the specimen will be analysed with the computed tomography (CT). This technique, together with the software MAVI (, Modular Algorithms for Volume Images) allows to measure directly the fibres concentration and their orientation. Particular interesting is to analyse the failure cross section and in the neighbourhood areas.
The computed tomography has demonstrated its potentiality for ordinary and for ultra-high performance fibre reinforced concrete as reported in . Since it is quite hard to correlate the presence of fibre in the specimen and the tensile creep in cracked cross section, it was decided to investigate the orientation after the
Fig. 5 Fibre 3d rendering reconstruction (fibre length 6 mm, 0 0.175 mm), Schnell 
sustained load tests. Considerations about the fibre orientation and the post crack tensile behaviour are well described by Frettlohr . The biggest difference between ordinary fibre reinforced concrete and UHPC is the larger amount of fibres. This complicates the analyses of the single fibre. Moreover the dense structure of the concrete limits the size of the cross sections up to a dimension of about 40 mm. This is the reason why the axial tension specimens are limited in their cross section (Fig. 1). Figure 5 shows how a 3D reconstruction of the fibres in a 50 x 50 mm specimen separated from the concrete. With this reconstruction is possible to divide the volume in different areas and calculate the fibre concentration and the orientation along the three principal directions.