Manufacturing, fibre anisotropy and fracture of hybrid fibre concrete

In the paper an overview is presented of recent results obtained in a comprehensive research (in progress) on the relation between manufacturing processes, fibre anisotropy and fracture properties of hybrid fibre concrete containing three different types of steel fibres. Since manufacturing relates to specific fibre orientations and thus to specific fracture behavior, these parts of the research are presented together in this paper. The experiments conducted confirm that a strong increase of flexural strength and ductility can be obtained when fibres cocktails are applied. The fibres tend to align along the walls of moulds, and it is shown that these highly reinforced surface layers add significantly to the strength of the beams. The fibre alignment can be affected by the viscosity of the concrete mixture in the fresh state, which allows to ‘place’ fibres at those locations where they are most needed. Finally, impregnation experiments show that pre-peak cracking is indeed in the form of multiple cracking, which localize into a major crack beyond peak. The localized crack is prevented to open rapidly by the bridging of the largest fibres present in the fibre cocktail.