Determination of the quality parameter ranges of reinforcing bars used in Uganda's construction industry

Abstract

Uganda's construction industry faces a serious concern with substandard reinforcing bars (rebars), leading to building collapses, fatalities, and financial losses. A study was conducted to determine quality parameter ranges of reinforcing bars by determining mass per unit length, testing mechanical properties, analyzing chemical composition, and evaluating conformity to standards. The goal was to prevent future collapses and safeguard lives and investments. Experiments focused on 10 mm and 12 mm rebars, commonly used in various construction projects, unlike larger rebars typically made from imported billets. Samples from four hardware stores representing different manufacturers were tested, with initial measurements taken using a meter rule and weighing scale to assess length and mass. Later, the mass per unit length was calculated and it was found that the obtained results were within acceptable ranges from 0.567 kg/m to 0.667 kg/m for rebars with diameters of 10 mm and 0.838 kg/m to 0.938 kg/m for rebars with diameters of 12 mm based on US-EAS 412-2-2022. Mechanical properties like yield stress, tensile strength, elongation, and stress ratio were tested on a universal testing machine and they revealed acceptable yield stress values above 500 MPa and elongation above 14% across all samples. While all rebars exhibited yield stress above the minimum allowable limit of 500 MPa based on US EAS 412-2-2022, some did not meet the stress ratios like A10, B12, C10, C12, and 012, which were below the specified minimum 1.15 outlined in US EAS 412-2-2022. Bending tests indicated no observable cracks in the rebars. On the other hand, using a spectrometer, the chemical composition of steel rebars was analyzed, and it was revealed that some elements were slightly below allowable limits. The analysis focused on major alloying elements, including C, Mn, Si, P, S, Cr, Mo, Ni, V, and Cu. Rebar A10's manganese content was significantly below the minimum allowable limit of 1.6% (at 0.75 %).Other elements (C, Si, P, S, Cr, Mo, Ni,V, Cu) were within allowable minimum limits, aligning with US EAS 412-2-2022 standards. The carbon equivalent value (CEV) was then calculated and used to evaluate weldability, which ranged from 0.315 to 0.376, all falling within acceptable established standards. Notably, while three rebars A12, B10, and 010 met the specified quality parameters, the other five rebars A 10, B 12, C 10, C 12, and 012 did not conform, primarily due to low-stress ratios below 1.15, a critical factor affecting ductility and load absorption during seismic events. This research could improve the rebar quality and help prevent future building collapses, protect lives, and safeguard investments. The findings emphasized the need for stricter quality control in rebar production and selection to avoid structural failures.