Shear strength of concrete beams reinforced with steel bars milled from scrap metals

The paper reports a study on the shear resistance of concrete beams reinforced with mild steel bars that are milled from scrap metal such as old vehicle parts and obsolete machinery. It has been previously reported that because the chemical compositions of carbon, sulphur and phosphorus in these reinforcing steel bars exceed the maximum allowable limits, the characteristic tensile strengths are too high and ductility too low for standard mild steel. Concrete beams reinforced with such bars to resist flexural tensile and shear stresses were tested under a two-point loading system to provide a central constant moment region and outer shear spans. Tested beams exhibited little deflection and very low ductility prior to collapse. Experimental failure loads for the beams averaged 123% of the theoretical failure load, which was generally governed by either shear or yielding of the tension steel. Shear failure was mostly initiated by diagonal tension cracks, followed by either crushing of the concrete, or splitting of the concrete over the longitudinal tensile bars near the supports. Failure of the beams was brittle and the post-cracking strain energy absorption averaged 357.9 Nm. At failure the maximum crack width in the beams ranged from 1.12 to 5.0 mm, the largest sizes forming in the diagonal shear cracks.