Effect of Elevated Temperatures on the Bond between Galvanized Steel Rebars and Concrete

Hot-dip galvanized steel rebars are widely used in corrosion-prone environments due to their enhanced durability. However, the relatively low melting point of zinc raises concerns regarding their bond performance with concrete under elevated temperatures. This study experimentally investigates the bond behavior of galvanized steel rebars in concrete under fire exposure. Flexural bond tests were conducted on reinforced concrete specimens incorporating 12 mm and 20 mm diameter rebars. Two heating regimes—a slow heating rate of 2 °C/min and the ISO 834 standard fire curve—were employed to examine the influence of heating rate and associated thermal gradients. Bond strength was evaluated under thermal steady-state conditions at steel–concrete interface temperatures ranging from 20 to 500 °C, and the performance of galvanized rebars was compared with that of conventional thermo-mechanically treated (TMT) steel rebars.The results indicate that galvanized rebars exhibit lower bond strength than conventional rebars at ambient temperature. However, at elevated temperatures, the reduction in bond strength is less pronounced in galvanized rebars. Microstructural investigations using scanning electron microscopy revealed that increasing temperature leads to progressive oxidation of the outer galvanized layers and a significant increase in surface roughness. These changes are likely to contribute to the improved retention of bond strength at elevated temperatures in comparison to conventional steel rebars.