Bond Deterioration between Corroded Reinforcing Bars with Variable Diameters and Concrete at Elevated Temperatures

Abstract

The fire resistance of corroded reinforced concrete has attracted extensive attention, mainly due to the frequent occurrence of fires in old structures. However, using the postfire bond strength to predict structural capacity during fires leads to inaccurate results. Thus, in this study, an accelerated corrosion test and an eccentric pullout test were performed under steady-state conditions from 20°C to 800°C. The test results indicated that compared with the bond strength at 20°C, the bond strength at 200°C decreased by 6% for the corroded specimen (corrosion level below 4.3%) and increased by 11% for the uncorroded specimen. When the temperature exceeded 500°C, the storage modulus and bond strength decreased 55%. Increasing the rebar diameter reduced the bond strength by approximately 29% and made the descending section of the τ-s curve steeper during exposure to fire. The energy dissipation at 100°C was larger than that at other temperatures, and the bond stiffness at 600°C was 12.5% of that at 20°C. The reduction in bond stiffness postponed the development of splitting cracks, restricted the crack width, and prevented splitting failure. Subsequently, temperatures dependence was analyzed and methods were proposed for the calculation of bond strengths at elevated temperatures. The results obtained with the proposed continuous bond-slip model were in satisfactory agreement with the pullout test results. Finally, the comparison of integral absolute error indicated that the model could be used to make accurate calculations of bond strengths during fires.