The use of polymer adhesives during the strengthening of 30-year-old prestressed concrete bridge girders is described. The single-T-shaped specimens strengthened in this study were saw-cut from prestressed concrete double-T girders that had been removed from a bridge originally designed for H-15 highway loading and opened to traffic in 1969. Over time, the bridge had been severely overloaded, resulting in numerous flexural and shear cracks in the stems of each girder and large concrete spalls at the tension faces. In 1998, several damaged members were replaced. To investigate the feasibility of repairing or strengthening similar members in the future, the damaged members were retrofitted with carbon fiber-reinforced polymer (CFRP) sheets and then load tested under service and ultimate load conditions. Polymer adhesives were used to seal all visible cracks in the stems, to inject epoxy into all sealed cracks, to fill spalled areas in the tension face of the stems, to apply longitudinal and transverse CFRP sheets to the stems of the members, and to install near-surface-mounted reinforcement (NSMR) in one of the specimens. Results from load tests indicate that excellent bond was consistently achieved between the CFRP sheets and the 30-year-old concrete surface and between the NSMR and surrounding concrete. The success of epoxy injection of the flexural cracks, however, varied. Specifically, the injected cracks in one specimen reopened at an applied load well below the theoretical cracking load for the members.
Abstract