New technologies in civil engineering often come from the application of new materials. Since the end of the 1970s, Europe conducted research on the application of fiber-reinforced (FRP) composite materials in civil engineering. It has excellent strength ratio and stiffness ratio and excellent corrosion resistance. Fiber-reinforced(FRP) composite materials have been widely used in the pasting and strengthening of concrete structures. A new technology for reinforcing and strengthening old concrete bridges with fiber-reinforced composite materials has been formed, among which carbon fiber-reinforced composite materials (CFRP) are used more.

The basic material used for reinforcement of carbon fiber reinforced composite materials is continuous carbon fibers with high strength or high elastic modulus, which are arranged in bundles in one direction. Carbon fiber impregnated and cured with epoxy resin or carbon fiber cloth without resin impregnation and curing are collectively referred to as carbon fiber sheets. Paste the sheet with a specially formulated adhesive resin or impregnating resin on the surface of the bridge concrete component that needs to be reinforced. After the resin is cured, it will form a new force-bearing complex with the original component and work together.

The form of advanced FRP composite systems to strengthen the bridge

advanced FRP composite systems are mainly used for the reinforcement of basic components and nodes of concrete bridges. The reinforcement effect is mainly to improve the flexural bearing capacity, the shear bearing capacity of the component and the axial compressive bearing capacity of the compression component, and to improve the rigidity and ductility of the component. In addition, many indoor and field tests have proved that the crack width development of concrete members reinforced with carbon fiber sheets can be controlled.

Because advanced FRP composite systems, especially carbon fiber wrap, are light in weight and thin in thickness, and have a certain degree of flexibility, it is more flexible to strengthen the relevant parts of the concrete bridge. Carbon fiber sheets have different tensile strengths in each direction due to different carbon fiber arrangement directions. When the fiber direction and force direction of carbon fiber sheets are the same, the tensile strength is the highest. When the fiber direction is perpendicular to the force direction, its strength is the lowest. Therefore, when using carbon fiber sheets for reinforcement design, it is necessary to correctly grasp the direction of fiber arrangement. According to the calculation of the reinforcement of the concrete members, the continuous pasting or the way of pasting the carbon fiber sheets at intervals can be adopted. Research shows that the effect of strip reinforcement is better than that of the entire cloth.

Application of advanced FRP composite systems in strengthening concrete bridges

(1) Reinforcing concrete bridges with carbon fiber sheets is a new technology, which has become a rapid reinforcement method for highway bridges, which is suitable for the requirement of not affecting the normal operation of the bridge during the highway bridge reinforcement period. The carbon fiber sheet is light and does not require heavy equipment to be pasted on site. The construction is convenient and it is convenient for high-altitude operations under the bridge.

(2) For the reinforcement method of old concrete bridges on highways, the comprehensive method has a better application effect in engineering. That is, a certain reinforcement method is the main method, supplemented by other methods. This must be determined in accordance with the visual inspection, technical evaluation and reinforcement design requirements of the bridge site. At present, the reinforcement methods of pasting carbon fiber sheets are often supplemented by crack grouting and crack sealing.