With the increasingly busy traffic, some highway bridges have been overloaded for a long time, coupled with the occurrence of aging and damage, about 30% of the bridges in China are in an overwhelming state. If it is demolished and rebuilt, traffic interruption will occur, which will affect the development of transportation. Therefore, strengthening the old bridge is an effective measure to ease traffic.

(1) Reinforcement with carbon fiber composite material

Reinforcement and repair of carbon fiber composite materials is the use of resin materials to paste carbon fiber materials on the surface of structures or components to form composite materials, so that the original reinforced concrete and carbon fibers jointly form a force surface. This increases the shear and bending capacity of the bridge structure and improves mechanical properties.

From the late 1970s to the early 1980s, developed countries such as Rimage and Japan began to study the application of carbon fiber composites in the reinforcement and repair of concrete structures. China started to study this technology only in 1997. Although it started late and developed slowly in previous years, with the continuous progress of China's science and rapid development of economic construction, more and more universities and research institutes have invested in this technology. This research work has also achieved remarkable research results. China's civil construction market has the most potential, and the application of carbon fiber reinforcement technology in building structures will continue to grow.

Carbon fiber reinforcement is divided into two types: carbon fiber cloth reinforcement and carbon fiber plate reinforcement. The carbon fiber material used for reinforcement in actual engineering is mainly carbon fiber cloth. The main advantages are reflected in the following aspects:

①Reinforcement effect is obvious: Adopt epoxy resin to paste carbon fiber cloth and reinforced concrete members together, so as to achieve the effect of joint force, and the strength is obviously improved. For example, the bearing capacity and ductility of concrete structures and components have been greatly improved to achieve the purpose of reinforcement and repair.

② Corrosion resistance to acid, alkali and salt media: Carbon fiber cloth only uses epoxy resin during the reinforcement process, without the addition of metal materials, so it will not rust, and does not need the regular antirust maintenance like the steel bonding method. Moreover, carbon fiber is resistant to corrosion by acids and alkalis, and can be used to strengthen components in harsh working environments. It is especially suitable for areas with high air humidity and high salinity in coastal areas.

③Convenient and fast construction: Carbon fiber cloth has small density, light weight and good flexibility, so it can be taken to the construction site and cut according to the size of the site, which has strong operability. During the construction process, small electric tools can be used, and large equipment is not needed, and the construction is convenient. No on-site fixed facilities are required, less space is occupied, available operating space requirements are relatively loose, no wet work, and operation is relatively easy. The construction speed is fast. The ergonomics of carbon fiber reinforcement is 4-8 times that of steel reinforcement.

④ Keep the original structure unchanged and beautiful appearance: this operation is just to paste multiple layers of carbon fiber cloth on the surface of the original structure, and cut and paste the carbon fiber cloth according to the shape of the component. Without changing the original structure, you can also paint decorative materials and fireproof materials on the outer layer to Improve its ornamental and safety. In addition, carbon fiber prepregs are small and thin. The thickness of a single layer is only about 1.0 mm, and the mass per unit area is less than 1.0 kg (including resin). Therefore, the construction mass and volume are not increased after construction, and the epoxy resin is bonded. No anchor bolts are needed, no new damage to the original structure. Several layers can be pasted according to the force.

⑤ Prolong the service life of the concrete structure by closing the cracks generated by the concrete structure.

⑥ The bridge reinforced by carbon fiber composite material is easy to construct and the construction time is short.

⑦ Wide application. Carbon fiber composite materials are flexible for repair and repair, and are not restricted by the structural type, shape, and construction site of the component. They can be widely used for various reinforcement and repair, which is unmatched by any current method of structural reinforcement.