Carbon fiber reinforced materials are widely used in bridge reinforcement. As a commonly used reinforcement material, carbon fiber is much more resistant to corrosion than conventional reinforcement materials (such as steel plates). Wrapping carbon fiber on the outside of the structural member can effectively use its stability and its insensitivity to acid, alkali and temperature to protect the structure itself, reduce damage, enhance the durability of the structure, and extend the service life. However, carbon fiber has insufficient shear resistance and cannot be used in the shear resistance of the bridge structure. It will also fail when it is bonded with old concrete improperly. The effect of carbon fiber will also be affected by water intrusion in the beam.

The pros and cons of carbon fiber reinforced concrete bridges

The principle of carbon fiber reinforced concrete structure: when special resin is used to paste carbon fiber on the tensile surface of the concrete structure, the carbon fiber and the original structure form a new force-bearing whole. The carbon fiber and the steel bars bear the load together, reducing the stress of the steel bars, so that the structure can achieve the effect of reinforcement and reinforcement.

The main features of the pasted carbon fiber reinforcement technology:

Almost no increase in structural weight and cross-sectional dimensions;

Do not change the clearance height under the bridge;

Convenient construction;

Hardly cause new damage to the original structure;

Has good corrosion resistance, durability and fatigue resistance;

Excellent mechanical properties, can be effectively applied to a variety of structural reinforcement, including bending resistance, shear resistance, compression resistance, fatigue resistance, earthquake resistance, wind resistance, control of the expansion of cracks and deflection, and increase the ductility of the structure. According to the force analysis, multi-layer paste reinforcement can be performed, and its directionality can also be flexibly grasped.

In addition, the carbon fiber is soft in texture and can reinforce various concrete structures without changing the shape of the structure. After reinforcement, it can be coated with concrete mortar, or the pattern requires various paints to repair and strengthen without leaving traces.

Reinforcing method with carbon fiber cloth:

Flexural reinforcement, the carbon fiber sheet is attached to the side under tension;

Shear reinforcement, paste vertically on both sides of the beam, or form a V-shaped ring wrap on the bottom surface, which is equivalent to adding shear studs;

Anti-crack reinforcement, paste along the vertical direction of the crack;

The columnar center compression member is reinforced, and the column center ring wraps and pastes;

For shear wall reinforcement, carbon fiber sheets are pasted along the direction of shear reinforcement on one or both sides of the shear wall.

The carbon fiber reinforcement effect is significant, but the following issues should be paid attention to in the actual bridge reinforcement project:

The use environment and construction conditions of carbon fiber are very different from those in the laboratory. In addition, the construction performance of the material itself affects the construction quality, so the design tensile strength of carbon fiber should be considerably reduced from the laboratory data;

The process level of the construction team is also a factor that affects the mechanical properties of composite materials, but it is not yet possible to conduct a quantitative evaluation;

At present, it is scientific and reasonable to use the partial coefficient method to define the influencing factors that affect the design strength of carbon fiber during the use of carbon fiber, but the specific values of these coefficients should be determined based on a large number of experimental values and scientific theoretical analysis.

Through continuous research on carbon fiber materials and continuous improvement of carbon fiber reinforcement methods, it is believed that carbon fiber reinforcement will become the inevitable trend of bridge reinforcement in the future.