Flexural Behaviour of Concrete Beams Reinforced With Rebars Milled From Scrap Metal

Abstract

Ductility index is imperative for structures and structural elements in service. Hence, a structure or structural element with inadequate ductility will experience brittle failure and lives jeopardized. As such, one cannot over-emphasize the ductility index of reinforced concrete beams subjected to large inelastic deformation. Reinforcing steel bars mostly used in the construction industry in Nigeria today are milled from recycling of scrap metals and currently sustains the steel sector. The study evaluated the flexural behavior of rectangular concrete beams with rebars obtained from recycling of scrap metal. This was achieved by designing the beam, produced eighteen samples (100mm x 200mm x 1000mm), six each with concrete strength of 20.33, 26.74 and 30 N/mm² and steel ratio (ρ) of 0.0058 to 0.012 respectively. The samples were tested under a four–point load experimentally. Load-deflection relationship, first crack load, ultimate load, deflection ductility index and stiffness of the beams were assessed experimentally. Test results showed the failure mode of most beams as ductile flexural failure accompanied by yielding of the tension steel preceding the crushing of concrete. The test samples has an ultimate capacity between 43.25 and 88.25Kn and its deflection ductility index is also between 1.73 and 2.38; while the loss in stiffness was influenced by the yield strength and percentage elongation of the steel bars. The effect of concrete strength and steel ratio on deflection ductility index shows that with increase in concrete strength, deflection ductility index increases, but decreases with increase in steel ratio. With a ductility index of 1.73 to 2.38 shows that the concrete beams reinforced with rebars milled from scrap metal is inadequate, cannot redistribute moment, a structural member not capable of resisting large displacement. This should be taken into consideration in the design of beams with such rebars. Key words: ductility index, Load-deflection response, concrete beams, rebars, scrap metal .