Tensile behaviour of ultra-high-performance steel fiber reinforced concrete

Recent developments in the area of ultra-high-performance steel fiber reinforced concrete (UHP-SFRC) has enabled a reduction in the use of steel reinforcement and has led to enhanced ductility and toughness of structural components owing to its resilient tensile behaviour. This paper presents the results of an experimental study that was conducted to investigate the tensile behaviour of UHP-SFRC. Four commercial mixes and two in-house mixes were evaluated using the procedures prescribed in the 2019 edition of Annex U of CSA-A23.1 and in Annex 8.1 of CSA-S6 2018. The tensile strength of UHP-SFRC was quantified and correlated through the direct tension test, splitting test, inverse analysis of four-point bending tests using either code expressions or nonlinear finite element analysis, and a calibrated empirical expression that links this property to the cylinder compressive strength. In addition, the effect of important parameters on flexural strength including casting methodology, volumetric ratio of steel fibers, and aspect ratio (shear span to depth ratio) of bending prisms have been assessed. The casting methodology affected the fiber distribution, an attribute that directly relates to flexural strength. Prisms containing 1% steel fibers by unit volume failed in a relatively brittle manner and possessed less flexural strength than the prisms containing 2% steel fibers. Prisms with an aspect ratio of 1 tended to develop greater flexural strength than the prisms tested with an aspect ratio of 2. The tensile strength obtained from inverse analysis is generally greater than the strength obtained from the direct tension test, the finite element analysis, and the calibrated empirical expression. Furthermore, it was determined that tensile strength obtained from the splitting test should be multiplied by a correction factor of ≈1/π, to match the strength obtained from the direct tension test. The majority of the mixes tested exhibited a tension hardening behaviour with a hardening ratio greater than 1.1 and an ultimate tensile strain greater than 0.001.