Inadequate design and construction, reinforcing-steel corrosion, change of use, and deterioration due to a variety of environmental effects all create a need for structural strengthening of concrete. Historically this strengthening has been done by conventional means, such as section enlargement, external post-tensioning, and steel-plate bonding. However, more and more engineers are turning to fiber-reinforced polymer (FRP) materials for concrete strengthening, repair, and retrofitting.
Three forms of FRP systems are currently in use for concrete strengthening: fabric sheets, pultruded strips, and prefabricated elements. One or more layers of FRP fabric or prefabricated FRP elements can be wrapped around or placed over weakened concrete members to form an external strengthener that helps support loads and prevent excessive deflections. In addition to rapid installation, FRP materials offer the advantages of superior strength and stiffness-to-weight ratios and a high degree of chemical inertness in most environments.