Key issues in the use of fibre reinforced polymer (FRP) composites in the rehabilitation and retrofitting of concrete structures

Abstract

Fibre reinforced polymer (FRP) composites were first used in the building industry during the late 1960s to construct all-composite buildings; also at this time, the construction industry proposed that rebars for reinforcing concrete should be made from composite materials and prestressing tendons for concrete beams should also be manufactured from FRP composites. However, it was not until the mid-1980s that a few research/design teams throughout the world seriously investigated the use of composites to prestress concrete beams and to utilise the material in conjunction with the more conventional materials. FRP composites were seen at that time as materials with a high strength and stiffness and to have a high corrosion resistance; they could be tailored to any design requirement but their high cost was a drawback to their use. In addition, the attitude of the civil engineering industry generally was against the materials but in the late 1980s, composite materials started to have their first major successes in the field of flexural and shear strengthening and seismic retrofitting of degraded concrete structures. This initial thrust has now been extended to areas such as confining concrete columns and strengthening beam/column joints, but in spite of this FRP composites have not yet been fully accepted by all areas of the civil engineering industry. In the strengthening and seismic retrofitting area of civil engineering, the cost of the FRP material is only a relatively small percentage of the overall cost for the work, and because of its physical properties, its fabrication on site can be undertaken much more speedily than if a more conventional material were to be used. Its low weight has an economic benefit in decreasing the erection time and reducing any costly closure period of the highway. This chapter discusses the mechanical and in-service properties of advanced polymer composite materials and their components, their long term loading characteristics and the manufacturing techniques available for use, specifically in terms of rehabilitation and retrofitting of reinforced and prestressed concrete structures. It considers the preparation of the surfaces of the concrete, and of the polymer composite plate, and suggests ways of joining the plate to the adherend. Finally, it anticipates future trends in the field of upgrading structural members.