Bond Strength of Tension Lap Splices in Pre-Damaged Reinforced Concrete Beams Retrofitted with Carbon Fiber-Reinforced Polymer and Ultra-High-Performance Concrete

Although the bond strength between reinforcing bars and pre-damaged concrete affects the seismic performance of repaired concrete structures, few studies have focused on the bond performance between the reinforcing bar and pre-damaged concrete. In the present study, to evaluate the effect of retrofitting with carbon fiber-reinforced polymer (CFRP) or ultra -high-perfor-mance concrete (UHPC) on the bar bond strength, lap-splice tests were performed on 20 beam specimens. The beam specimens were pre-damaged until bond failure or reinforcing bar yielding, and then the retrofitted beam specimens were reloaded to evaluate the bond strength recovery. Specimens were divided into five groups according to the reinforcing bar diameter, use of stirrups along the splice length, and type of preloading. Four retrofitting methods- CFRP sheet (C), a combination of CFRP sheet and crack injection epoxy (CE), UHPC (U), and a combination of CFRP sheet and UHPC (CU)-were applied to each group after preloading. The test results showed that the bar bond strength was improved by the used retrofitting methods, particularly by the retrofitting method of CU. In the specimens with a 20 mm reinforcing bar diameter and slight pre-damage, the retrofitting methods of C and CE were appropriate to restore the bar bond strength. For the specimens with a 28 mm reinforcing bar diameter and serious pre-damage, the bar bond strength was improved by retrofitting with U and CU. To consider the effects of pre-damage and retrofitting with CFRP sheet and/or UHPC on the bar bond strength, a modification of the existing methods for bar bond strength was proposed. The proposed method predicted the test results well.