Carbon fiber reinforcement technology

Carbon fiber reinforcement technology as a new and efficient reinforcement technology. By sticking carbon fiber material on the surface of the member to make it firmly combined with concrete, it can improve the mechanical performance, achieve the purpose of strengthening the structure, improving the bearing capacity and seismic resistance.

Carbon fiber reinforcement technology is suitable for the reinforcement and repair of various structural types and various structural parts. Structures such as beams, slabs, columns, roof trusses, piers, bridges, cylinders, shells, etc., require that the strength of the base concrete is not lower than C15. In addition, some mechanical properties of brick masonry can also be reinforced with carbon fiber.

The working principle of carbon fiber reinforcement technology is to make carbon fiber into carbon fiber cloth. Combined with the relevant factors of the damage to the building components, a certain method is used to attach it to the surface of the building component, so as to spread the force and achieve the reinforcement effect.

First of all, carbon fiber cloth and bonding materials need to be used in carbon fiber reinforcement technology. Due to their different roles and characteristics, they need to form a perfect whole during the manufacturing process, which can enhance its stability and effective To avoid the breaking problem of single fiber under strong action.

Secondly, the carbon fiber cloth has high initial strength, strong load pulling force, and little change due to external force. The adhesive material is easily affected by external forces in the force transmission. In order to avoid the peeling of carbon fiber and building components under external force, Adhesive materials require very high initial properties and strength.

It is a technological innovation, because the traditional reinforcement method is often passively stressed, and the prestressed carbon fiber board reinforcement technology is an active force, the prestress applied by the carbon fiber board through the tensile anchoring end and the carbon sheet rubber work together and It is evenly and effectively transmitted to the beam body, which improves the bearing capacity of the component, and at the same time reduces deflection and deformation, or closes the cracks of the component, thereby improving the rigidity of the component and improving the performance at the stage of use.

CFRP composite strengthening bridge

General situation of Engineering

The maintenance renovation of the irrigation canal bridge of the North Jiangsu Expressway has been the first maintenance since the bridge was opened to traffic in December 8, 2000. In order to ensure the normal, safe and smooth transportation of this important north-south highway, the bridge maintenance repair project adopts non closed construction method with a construction period of 1 months.

Reinforcement time

September 2014

Reinforcement method

Strengthening method by bonding carbon fiber cloth

Material selection

HM carbon fiber cloth, HM carbon fiber glue

Application of strengthening beam bridge with carbon fiber plates

Bridge Overview 

A bridge was built in 1998. The original design load is automobile-over 20 tons, trailer -120 tons, simple support structure. The standard span of the bridge superstructure is 20m and 25m, the beam height is 0.9m and 1.0m respectively, with a total of 78 holes, and the total length of the bridge is 1951.6m. The whole bridge is divided into two, the two bridges have the same layout, and the total bridge has a total of 982 hollow slabs. The width of the middle plate is 1.24m and the width of the side plate is 1.64m. The post-tensioned partial prestressed concrete members of Class A are originally designed with concrete strength grade 40, the standard strength of prestressed steel strands is 1860 MPa, and the ordinary steel bars are HRB335 steel bars.

Bridge disease

Inspection of 982 post-tensioned prestressed hollow slabs of the full bridge revealed that there were transverse cracks at the bottom of 138 hollow slabs (see Figure 1), accounting for 14.05% of the total number of hollow slabs. The cracks are distributed within 5 m from the mid-span cross section, and are mostly located at the location of the transverse stirrups of the bottom plate, with a spacing of 0.2-3 m and a crack width of 0.02-0.22 mm. Among them, the cracks with a width of 0.02-0.10 mm account for more than 90% of the total, the crack depth is 20 mm-34 mm (the thickness of the protective layer is 35 mm), the cracks extend along the beam height to the web 0.4 y 0.6 m, and some cracks penetrate the bottom plate to form a U shape crack.

According to the inspection results of cracks, the width of the cracks has not met the requirements of the regulations, the actual bearing capacity of the prestressed hollow slab structure has significantly decreased compared with the design bearing capacity, so the prestressed slab beam should be replaced or repaired and strengthened

Bridge strengthening

Consider factors such as construction period, construction cost, the impact of structural diseases, material degradation, and whether new and old materials can be effectively bonded and coordinated after reinforcement. After comparison and selection of the scheme, 15 slab beams with dense cracks at the bottom of the beam and severe deflection were replaced with the main beam. The main beams with transverse cracks at the bottom of the remaining beams are reinforced with non-prestressed carbon fiber plates to improve the bearing capacity of the structure.

Paste a layer of 100mm wide and 1.4mm thick carbon fiber plate to the bottom of the beam.

Strengthening beam bridge with carbon fiber plates

After the carbon fiber plate is used to reinforce the slab beam, the deformation and strain of the bridge meet the design load standard requirements, and the flexural bearing capacity of the bridge is improved after the reinforcement. Since the bridge was reinforced and opened to traffic two years ago, no new disease has appeared on the bridge, and cracks at the bottom of the beam have not expanded. Therefore, the reinforcement method of pasting carbon fiber sheet has a good inhibitory effect on the development of existing cracks and the generation of new cracks. On the basis of reasonable economy and simple construction, the use of carbon fiber sheet to strengthen the bridge can meet the operational requirements, and the bridge is in safe use.

Strengthening concrete column reinforced with carbon fiber wrap

column reinforced with carbon fiber wrap

column reinforced with carbon fiber wrap

Since most of the engineering building structures use reinforced concrete columns as their primary load-bearing form, it has practical engineering significance for their reinforcement research.

Technical characteristics of reinforced concrete column with carbon fiber wrap

First, the characteristics of carbon fiber materials. 

Carbon fiber wrap has small thickness, light weight, good flexibility, acid and alkali resistance, high temperature resistance, fatigue resistance and creep resistance. It can meet the requirements of bending, compression and earthquake resistance, and at the same time can resist the corrosion of various acids, alkalis and salts that the reinforced column is often subjected to. Carbon fiber wrap forms a second protective layer on the surface of the concrete column, which enhances the durability of the concrete. It has little effect on increasing the weight of the column and the cross-sectional size, and meets the appearance requirements of the reinforcement.

Secondly, in terms of stress characteristics.

Carbon fiber wrap has high tensile strength and is easy to bond well with the concrete surface. After transversely surrounding the column, the stress state of the concrete is changed from two directions to three directions, becoming constrained concrete, which has been greatly improved in both bearing capacity and ductility

Finally, engineering application.

It has the characteristics of non-destructive reinforcement of the original structure, easy construction and easy guarantee of construction quality. Unlike other reinforcement methods, carbon fiber wrap reinforces the entire construction process without large machines and wet operations, does not require a large number of fixed safeguards, and has a small occupation rate and high work efficiency. In terms of reinforcement quality, even if the surface of the reinforcement member is not flat, due to the flexibility of the carbon fiber wrap material, the adhesion efficiency can be guaranteed, and the maintenance cost of the investment in the later period is lower and the service life is longer.

Carbon fiber wrap for structural reinforcement technology

Carbon fiber reinforced polymer

Carbon fiber structure reinforcement technology refers to the use of high-performance adhesives to paste carbon fiber wrap on the surface of building structural members, so that the two work together. Improve the load-bearing capacity of components (bending, shearing), so as to achieve the purpose of strengthening the building. Carbon Fiber Reinforced Polymer (CFRP), also known as Carbon Fiber Reinforced Plastic, is made of epoxy resin with high tensile strength carbon fiber bundles. Carbon fiber wrap is a widely used product.

The use of carbon fiber wrap reinforcement has the following advantages: high strength and good effect. After reinforcement, the corrosion resistance and durability of the structure are greatly improved. Light weight, basically does not increase the structure weight and cross-sectional size. Good flexibility, easy to cut, wide range of application; convenient construction, easy to operate, and good economy. The construction period is short.

The main performance indexes of carbon fiber wrap for structural reinforcement are shown in the table

The durability of reinforced concrete with carbon fiber 

After the introduction of carbon fiber wrap reinforcement technology in my country, its application in civil construction structures, especially the reinforcement and repair of concrete structures, has developed rapidly. Moreover, the durability of concrete structures reinforced with carbon fiber wrap has attracted more and more attention. The carbon fiber wrap reinforcement method adopts a specific method to arrange continuous carbon fibers unidirectionally to form a reinforcing reinforcement material, and uses a two-component epoxy resin to adhere to the outer surface of the treated structural member to improve the structural function.

At present, the construction of carbon fiber reinforced and repaired concrete structures applied in China basically adopts a three-step method, that is, on the basis of the base treatment, the base resin with different properties and functions, the leveling material, and the impregnating resin are used to paste the carbon fiber wrap on the surface of the concrete. After the resin is cured, it can improve the load-bearing capacity of the component, improve the form of stress, improve the performance or anti-corrosion. Based on this construction method, the bonding interface performance of various materials is crucial. The durability of the reinforced concrete structure with carbon fiber wrap mainly depends on the durability of the carbon fiber wrap material and the durability of the bonding interface with the concrete.

Carbon fiber reinforced steel structure

The commonly used steel structure reinforcement method is to add welded steel and steel plates. This method will increase the size of the structure to a certain extent, resulting in an increase in the weight of the structure and a change in rigidity, resulting in the redistribution of the internal force of the structure. And in the construction, we must rely on mechanical equipment, especially when working at heights, with certain difficulty and danger. The carbon fiber wrap is used for reinforcement and reinforcement, which can be done manually, and has good corrosion resistance, and there will be no corrosion after steel plate reinforcement.

Carbon fiber reinforced masonry structure

Brick-concrete structure is widely used in my country. Reinforcement and restoration of existing brick-concrete buildings is a hot issue generally concerned by the construction engineering community. The use of carbon fiber wrap to reinforce and repair brick masonry is still in the initial stage of experimental research internationally, and the research on this technology in China is still blank. Carbon fiber wrap reinforced masonry structure technology has the advantages of not increasing the weight and volume of the components, high strength and efficiency, convenient construction, good corrosion resistance and durability, and wide application range, and has broad application prospects.

Carbon fiber wrap is a very effective reinforcement method for enhancing the seismic resistance of brick masonry structures. The cracking load (limit load) of the carbon fiber reinforced wall is significantly higher than that of the unreinforced wall.

When carbon fiber wrap is used to reinforce brick walls, the larger the width of the wrap, the more obvious the reinforcement effect. The carbon fiber wrap improves the stress state in the wall through the tension bar mechanism in the truss model, thereby improving the shear capacity of the member. In addition, by restricting the development of cracks in the wall, the crack resistance of the component is also improved. Carbon fiber wrap is used to reinforce the brick masonry structure, and the reinforcement at both ends of the fiber wrap is very important. Because when the bond between the fiber wrap and the masonry breaks, the energy is suddenly released and severe brittle failure occurs, so ductile anchoring at both ends of the carbon fiber wrap is required. Carbon fiber wrap can be used not only to reinforce and repair the existing brick-concrete structure, but also to reinforce concrete small hollow block walls.

Conclusion

Carbon fiber wrap has good performance in the reinforcement and repair of various structures, and has good durability. It can solve the reinforcement and repair problems of many special projects and has great application potential. Although the cost is high at this stage, with the further research on the performance and construction technology of carbon fiber wrap, and the development of production technology, the carbon fiber wrap reinforcement and repair technology will be more and more widely used.