Identification of tensile behaviour of SFR-SCC: direct vs. indirect tests

Identification of tensile constitutive relationship of fibre reinforced concrete is a crucial point to address structural design with SFRC material and actually represents its key distinctive feature with respect to plain concrete. As a matter of fact, as well known, the tensile fracture toughness of the latter is usually neglected in design. Several guidelines and recommendations have been issued, all over the world, addressing the aforementioned issue and prescribe either 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 this paper the aforementioned issue has been investigated with reference to a typical FR-SCC mix and 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 effects of the orientation of fibres on the material properties, identified as above.