Examining the Geometrical Properties, Chemical Composition, and Mechanical Properties of Local Reinforcing Bars in Ghana

Abstract

Steel is used extensively as a concrete reinforcing material in the construction industry in Ghana. Aside from its use as a reinforcing member, many steel-framed structures are also springing up, particularly in the industrial areas of the country. To address the high-demand for reinforcement, several steel manufacturing companies manufacture mild steel bars locally from recycled scrap metals to supplement the tonnage that is imported. However, the quality standards of these reinforcing bars produced in Ghana have been extensively criticized in recent times by the general public, professional bodies, and practitioners in the construction industry. In this research, mild reinforcing bars from three local milling companies randomly classified as STSL, B5PL, and FBML were examined to determine their physical properties (size and surface geometry), chemical composition, and mechanical properties. Similar tests were also conducted on imported bars from a foreign company classified herein as AM. It was observed that the locally manufactured reinforcing bars had actual bar diameters smaller than their nominal sizes with a significant reduction in diameters. These significant reductions in bar diameters have a great impact on the strength and capability of a structure to withstand all anticipated loading. The imported bars however had actual sizes almost equal to their nominal sizes. Also, the rib height and rib spacing of the locally manufactured bars were found to be inconsistent. This observation could significantly affect the bond strength of structural elements constructed with these bars. Additionally, the locally manufactured mild steel bars had higher percentages of carbon above the recommended 0.25% in the British and Ghana standards. This increased carbon content increases the yield and maximum tensile strength of the steel or its ability to support more weight but renders the steel bar brittle and unweldable. Furthermore, the locally manufactured mild steel bars had yield and maximum tensile strength higher than the recommended limits of 250 N/ mm2 and 485 N/mm2, respectively, as in the British and Ghana standards. The imported high- tensile bars recorded a minimum tensile strength of 609.88N/mm2 satisfying the minimum requirement. As the Government of Ghana takes steps to ban the importation of reinforcement bars into the country, the Ghana Standards Authority must ensure that locally manufactured bars satisfy the approved criteria to avoid structural failures caused by the use of sub- standard steel bars.