Implications of test methodology on post-cracking and fracture behaviour of Steel Fibre Reinforced Concrete

It is now universally recognized that the mechanical, cracking and fracture, properties of Steel Fibre Reinforced Concrete (SFRC) are far superior to those of plain concrete. The use of SFRC contributes effectively to preserve the structural stability and structural integrity of concrete elements and improve their ductile behaviour. To optimize the performance of SFRC in structural members it is necessary to establish the mechanical properties very precisely. The best test methodology to evaluate the post-cracking and toughness properties of SFRC is the beam bending test. Design codes recommend one of two bending test configurations: the three-point or the four-point bending test. The results obtained from these two test configurations are not identical. The overall focus of this paper is to evaluate the contributions of fibres to the post-cracking and fracture behaviour of concrete as determined by the two different standard test procedures. To achieve these aims plain and fibre concrete specimens were tested. All the test specimens were extensively instrumented to establish the strength properties, crack tip and crack mouth opening displacement, post-cracking and fracture behaviour. The results of the two types of bending tests were then critically analysed and evaluated to identify the differing effects of the bending load configurations on material and structural behaviour. SFRC specimens subjected to four-point bending test showed higher stress values compared to those obtained from the three-point bending tests. The first crack strength values evaluated following the two standards are close with an improvement of 10% for the European standard.