The content sand of total aggregate was varied from 0-100 Vol.-% and different types and contents of the steel fibres were tested. The applied fibre contents were 1.5 and 3.0 Vol.-% of the granular skeleton. It was not possible to test 3 Vol.-% for fibres having an aspect ratio of 60 or higher since fibre clustering counteracted a homogenous distribution of the fibres. Fig. 4.5 shows the effect of different sand contents and fibre types (at 1.5 Vol.-%) on the packing density. The average of three measurements and the variation are summarised in Appendix C (Tables C4-6).