Flexural Behaviour of Concrete Beams Reinforced With Major Steel Bars under Normal and Corrosive Operational Conditions

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Quality assurance of construction materials is very fundamental for structural safety, reliability, serviceability, and durability of constructed civil infrastructure. Inflow of defective or substandard building and construction materials into the industry, particularly reinforcing steel bars, is responsible for many structurally deficient constructed facilities which often lead to failure or ultimate collapse of reinforced concrete (RC) structures. Characterization of steel rebars from two major manufacturers into Botswana construction industry, designated herein as M1 and M2, were conducted as a basis for the evaluation of the quality assurance and control of the products. The flexural behaviour of their respective RC beams, designated herein as B-M1 and B-M2, of dimension 150 × 200 × 3000 mm and subject to four-point loading tests were determined under normal and artificially induced corrosion conditions to assess the influence of steel rebars M1 and M2 on the stiffness and load-carrying capacity. The average yield strengths of steel reinforcing bars were 427 N/mm2 for M1 and 459 N/mm2 for M2. The moduli of elasticity for M1 and M2 were 203 GPa and 205 GPa, respectively. The percentage elongation was found to be 7.93% for M1 and 7.24% for M2. The flexural strength of beams reinforced with M1 was 7% and 16.5% lower than RC beam with M2 under normal and accelerated corrosion of 5% of NaCl solution for 60 hours condition, respectively. The flexural behaviour of RC beams reinforced with B-M1 had a lower flexural strength under both normal and corrosive environmental conditions as compared to B-M2. The flexural strength of B-M1 had reduced from 48.5 N/mm2 to 41.0 N/mm2, while B-M2 reduced from 52.2 N/mm2 to 49.2 N/mm2. This represented loss of load-carrying capacity of 15.4% and 5.8% for B-M1 and B-M2 respectively due to exposure to corrosive environment. The findings revealed disparity in bending capacity due to the low interfacial bonding due to reduced relative rib areas. A more intensive quality control of imported steel should be ensured at the ports of entry by relevant regulatory agencies.