Bond strength of steel bars in steel-fibre-reinforced normal and self-compacting concretes

Pull-out tests were conducted to assess the bond stresses between two different sizes of steel bars and normal concrete (NC) and self-compacting concrete (SCC) with and without steel fibres (SFs), considering different conditions. The results showed that the pull-out capacities of the pre-cracked specimens were reduced by 20.4% when compared with uncracked specimens. Moreover, the pre-cracked NC specimens exhibited 10% lower tensile strength than their SCC counterparts. In addition, the specimens with SF had a higher bond stress than those without SF. Additionally, an increase in bar diameter from 12 mm to 16 mm led to a 22% improvement in bond stress. In summary, the addition of SFs to concrete generally enhanced the bond stress between the rebars and the concrete, with macro SFs exhibiting a particularly notable effect, leading to an 18% increase in bond. ACI 318-19 was found to produce conservative results of the developed steel bar length with safety margins of 120% and 79% for regular and pre-cracked specimens when compared with the expressions proposed in this work. Comparing available test results with the proposed models, the test results were very close to or more than the proposed models' results, depending on the bar diameter.