Bond strength of reinforcing steel bars milled from scrap metals

In many poor developing countries, reinforcing steel bars are milled using scrap metal from obsolete vehicle parts and machinery. In Ghana, these bars which are classified as mild steel, are normally milled with ribbed surfaces similar to standard high-yield steel bars to enhance their bond with concrete. Hitherto there has been inadequate information on the actual physical behaviour including the bond properties of these reinforcing steel bars, which are already in use in structural concrete. This paper presents a description of the experimental investigation of the anchorage bond resistance and slip characteristics of the steel bars in beams and pull-out specimens. The results of the study have shown that the average anchorage bond strength of the bars developed at ultimate steel stresses is higher than that of mild steel but close to standard high-yield deformed bars. The beam tests gave lower values of bond strength at relatively lower steel stresses, and averaged about 50% of the pull-out bond results. The large difference in the results of the beam and pull-out tests is due to the different concrete covers to the steel bars and the absence of concrete confinement usually developed by shear reinforcement in beams. Bond failure was mostly caused by the splitting of concrete.