SELF-COMPACTING FIBRE REINFORCED CONCRETE: IS THE MATERIAL REALLY ISOTROPIC

Identification of tensile constitutive relationship of fibre reinforced concrete is a crucial point to address structural design with this material and the determination of K factor introduced in Model Code 2010 for FRC remains an open question. The tensile fracture toughness can be identified by means of direct tensile or bending tests, or both, also in order to discriminate whether the composite behaviour is strain/deflection hardening/softening. When dealing with a Fibre Reinforced Self Compacting Concrete (FR-SCC) the flow-induced orientation of the fibres with respect to the applied tensile stress has furthermore to be carefully considered when experimentally identifying the tensile stress-crack opening relationships. In the paper the aforementioned issue has been investigated with reference to a typical FR-SCC mix by performing both indirect (bending and Double Edge Wedge Splitting) and direct tension tests. Comparison among the constitutive law identified through back analysis from bending tests and those directly provided by either direct or indirect tensile tests, always referred to the counted number of fibres on the fracture cross section of different specimens, will allow also a methodology to be proposed for the quantification of the orientation factor K, recommended by the Model Code to take into account the aforementioned effects of the orientation of fibres.