Bond strength behaviour of high strength structural lightweight concrete containing steel fibres with different geometries

This study was undertaken to investigate the bond strength behaviour of high strength lightweight concrete containing steel fibres in different geometries throughout a comprehensive experimental programme. Four lightweight concrete mixes were prepared and tested for the preliminary mechanical properties and pullout feature. In addition to the reference mix, the other three mixes incorporated micro, hook end and hybrid steel fibres at 1.5% by volume of the concrete mix. To evaluate the bond strength aspect, block specimens were reinforced with deformed steel bars of two diameters (12 or 25 mm). A comparison has been made with some relevant empirical formulas and codes of practice. The results obtained revealed superior performance for the fibrous lightweight concrete mixes in terms of the mechanical properties. The highest improvement in the compressive, tensile and pullout strengths reached 28, 163 and 225%, respectively. For the preliminary mechanical tests (i.e., compressive, tensile strengths), hybrid lightweight concrete mix showed the highest values, while hook end lightweight concrete mix seem to be the optimal for the case of pullout feature. Regardless of the geometry, the steel fibres increase the interior bond and prevent the propagation of cracks throughout tailoring mechanism. Most of the suggested formulas to predict the tensile and bond strengths need for amendments to be used for the case of high strength lightweight concrete.