Externally bonded steel plates, steel or reinforced concrete jackets, and external prestressingwere the traditional techniques used to strengthen or retroﬁt existing concrete structures to provide additional strength, compensate for construction design errors, correct deterioration problems, or improve the performance as required by code changes. These techniques were expensive because of the heavy equipment needed and, in most instances, did not provide a long service life. Corrosion of reinforcement, which is the common deterioration mechanism, affects the life cycle of steel plate in a similar manner. In addition, in certain cases such as strengthening of unreinforced masonry and concrete walls, the traditional techniques cannot be used. Highstrength composite materials, used by the aerospace industry for more than 40 years, are becoming the preferred materials for the repairs. Since composite materials are extremely light, the process of installing the composite onto a structure is simpliﬁed considerably and, inmost cases, heavy equipment is not needed for the repairs. The composites also have very high corrosion resistance. Although the materials are expensive, the ﬁnal cost of repair becomes competitive because of the ease of construction and the time savings. The most popular uses include:
• strengthening of reinforced and prestressed concrete beams for ﬂexure; • shear strengthening of reinforced and prestressed concrete beams; • column wrapping to improve the ductility for earthquake-type loading; • strengthening of unreinforced masonry walls for in-plane and out-
of-plane loading; • strengthening for improved blast resistance.