Strength and ductility characteristics of reinforcing steel bars milled from scrap metals

The physical and chemical properties of reinforcing steel bars milled from scrap metal such as vehicle parts and obsolete machinery in some developing countries were investigated. At present there is inadequate information on the actual behaviour of these reinforcing steel bars which are already in use in structural concrete for the construction of all types of buildings, bridges, hydraulic structures, etc., yet they are classified as mild steel in design specifications. The current state of the art can mean that design of reinforced concrete in such countries may not be fully reliable. The primary observations made with the physical properties are that for the type of mild steel produced in Ghana from re-cycled steel, the characteristic tensile strength is too high with very little elongation leading to limited ductility compared with standard mild steel and high-yield steel. The bars did not exhibit any necking down and cup and cone failure, similar to those observed in the case of standard mild steel plain bars. Concrete beams, reinforced with such bars were fabricated on the basis of under-reinforced concrete design, and tested under monotonic or cyclic loading to study the flexural behaviour of the beams. Tested beams exhibited little deflection and very low ductility and deformation prior to collapse. This paper presents a description of the experimental investigation carried out on the steel bars and reinforced concrete beams. Observations made on the physical and chemical properties of the steel bars, and the ultimate strength, mid-span deflections and crack width under monotonic and cyclic loadings of the beams are included.