Durability characteristics of concrete beams externally bonded with FRP composite sheets

The strengthening of concrete structures in situ with externally bonded fiber reinforced plastic (FRP) composite sheets is increasingly being used for repair and rehabilitation of existing structures. This paper provides information in the area of long-term durability of concrete beams externally bonded with FRP sheets. It was intended to study the effect of harsh environmental conditions such as wet/dry cycling using salt water on the performance of FRP-bonded concrete beams and on the interfacial bond between the fiber and the concrete. Concrete beams were strengthened with four different types of FRP sheet: two carbon and two glass. Three different types of two-part epoxy were used. Test variables included (1) the type of fiber; (2) the type of epoxy system, and (3) the environmental exposure condition. The specimens were conditioned in two different environments: (a) room temperature (+20 degrees C), and (b) 300 wet/dry cycles (salt wafer was used for the wet cycles and hot air at 35 degrees C and 90% humidity for the dry). At the end of each exposure, load-deflection curves of the specimens were obtained in order to evaluate their maximum capacity, stiffness, and ductility. The performance of the wet/dry exposed specimens was compared with those kept at room temperature. Results showed that specimens subjected to wet/dry environmental conditions and those kept at room temperature exhibited significant improvement in flexural strength when FRP sheets were bonded to the tension face of the concrete beams. However the specimens subjected to wet/dry conditions showed less improvement than chose kept at room temperature. None of the specimens failed clue to FRP rupture but rather due to the debonding between the FRP sheet and the concrete interface. The selection of epoxy was shown to be very important for using the FRP strengthening technique, especially in a marine environment. (C) 1997 Elsevier Science Ltd All rights reserved.