ABSTRACT Corrosion is the primary barrier for reduced safe service life of any reinforced concrete (RC) structure, particularly in the chloride-rich marine environment. Quenched and auto-tempered (QAT) reinforcing steel rebars offer superior strength and cost advantages over hot-rolled and normalized (HRN) counterparts, yet their corrosion susceptibility in aggressive environments remains a critical limitation. This study systematically investigates the corrosion behaviour of QAT (75 G) and HRN (60 G) steel rebars through a comprehensive experimental program. Microstructural characterization using optical microscopy revealed distinct case-core structures in QAT steels, which is absent in HRN steels. Tensile testing confirmed compliance with BDS ISO 6935-2:2021 standards for all grades. To evaluate corrosion behaviour, reinforced concrete specimens were cast, water-cured for 28 days, and subsequently exposed to a 3 wt.% NaCl solution for up to 10 weeks. Corrosion performance was evaluated through macrocell corrosion current measurements, complemented by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP). Post-exposure surface morphology analysis and Fourier Transform Infrared spectroscopy (FTIR) of corrosion products provided further mechanistic insight. X-ray diffraction (XRD) analysis revealed significantly higher compressive residual stress and microstrain in QAT steels, which showed strong linear correlations with corrosion current. Controlled additions of Cu, Cr, and Ni progressively modified rust layer and interface characteristics, consequently reducing corrosion current in QAT steels, with the best-performing alloy (75G-4: 0.15%Ni, 0.18%Cr, 0.18%Cu) achieving corrosion resistance comparable to HRN steel at only a ~5% cost increase. These findings demonstrate a practical cost-effective pathway toward high-strength, corrosion-resistant QAT rebars for durable RC structures in marine environments.
Islam et al. (Fri,) studied this question.