In recent years, fiber-reinforced composite materials (FRP for short) have been widely used in the engineering field to strengthen, repair and renovate concrete, steel or other material components. The reinforcement technology is to apply carbon fiber, a high-performance fiber, to civil engineering. The carbon fiber is pasted on the surface of the structure or component by using a resin-based bonding material to form a composite body FRP. Through the collaborative work with the structure or component, the purpose of strengthening the structural component and improving the force performance is achieved. This technology has excellent mechanical properties, excellent durability and good process performance. At present, carbon fiber materials have been widely used in the reinforcement of reinforced concrete structures, and good results have also been achieved in the reinforcement of metal materials and the control of temperature cracks in masonry.

Application of carbon fiber composite materials

Project 1

A steel mixer was originally built in the early 1970s with a span of 24m. The roof truss of the main and auxiliary spans is mainly a through-type reinforced concrete trapezoidal roof truss. After the reconstruction in 1987, the bracket is a deck-type parallel-chord reinforced concrete bracket with a span of 12m. The upper chord of the bracket supports the roof truss at the middle node. Some reinforced concrete roof trusses, brackets, have been reinforced with steel bars and angle steels. During the expansion and reconstruction in 1995, the original reinforced concrete columns were transformed, the original concrete columns were strengthened and the shoulder beams were increased, and steel small columns were added on top. The current problem with the plant structure is the increase in production load, the actual lifting of the crane and the increase in the frequency of operation, the mixing furnace cross-building structure has obvious shaking, and some structural components have different degrees of damage. For example, some concrete roof trusses and brackets have defects such as cracking, falling off, exposed reinforcement, and corrosion of steel bars.

Project 2

The first floor of a brick-concrete structure pump house has a building height of 4.5m, a building area of 120m2, and an anti-seismic design of 6 degrees. The design grade of concrete strength for ring beams and structural columns is C20, and the masonry is a 240ram thick brick wall, which is made of ordinary sintered red machine-made clay bricks MUIO0 and M5 mixed mortar. The roof slab is prestressed concrete hollow slab, flat roof, no heat insulation measures. It was built in 1986 and is in use today. There is a cooling water tower on the west roof of the pump house, the height of which is 3m, and the total weight of the tower is about 10t. There were cracks in the outer wall of the pump room, which formed an angle of about 45 degrees with the horizontal, and the cracks penetrated both sides of the wall. Individual concrete ring beams have cracks with a width of 0.2 mm. The position of the crack is at the lower corner of the window. The maximum width of the crack is 1cm and the length is 2.5m. The roof hollow slab cracked at the board seam, and the overlap between the two ends and the wall was obviously rubbed. Excluding the stucco layer on the wall surface, after testing the wall mortar strength and brick strength, the strength of the masonry mortar is low, the mortar joints are not full, and there are partial joints.

Main technical characteristics of carbon fiber composite materials

(1) High strength and high efficiency. Because carbon fiber cloth has the characteristics of high strength, high elastic modulus, low elongation, and light weight. It can make full use of its excellent mechanical properties to improve the bearing capacity, ductility, and crack resistance of concrete structures, and achieve the purpose of high-strength and efficient reinforcement and repair of concrete structures.

(2) Simple construction and short reinforcement period. Carbon fiber cloth is light in weight, and generally manual operation is used without the use of large construction equipment. The construction space is less restricted, and construction interference is less. In some cases, online construction can be realized. It only takes 2 to 3 days from sticking the carbon fiber cloth on the surface of the structural member to curing the adhesive and putting it into use.

(3) The construction quality is easy to guarantee. The construction quality standards of carbon fiber cloth reinforcement members are mainly reflected in the compactness of the carbon fiber cloth. Because the carbon fiber cloth is flexible, it is easy to stick on the surface of the structure, so that the carbon fiber cloth and the concrete surface can be glued densely. Under normal circumstances, it can be ensured that the effective bonding area of carbon fiber cloth is not less than 95%, which meets the quality requirements of carbon fiber cloth reinforced structure.

(4) Super waterproof and anti-corrosion effect. The carbon fiber cloth is glued and cured on the surface of the structure, and the epoxy resin is attached to the surface of the structure, which has a good waterproof effect and can prevent the corrosion of the steel bar. Carbon fiber materials have excellent corrosion resistance, so there is no need to worry about the corrosion of various acids, alkalis, and salts that buildings often encounter.

(5) Wide application range. Carbon fiber composite material strengthening and repairing structure technology can be widely used in various types of structures and components in different stress states such as beams, columns, plates, shells, arches, etc. in industrial, civil construction, water conservancy, electric power, bridges and other projects. Moreover, it is not restricted by the structural shape, such as round and complex curved surfaces, and carbon fiber cloth can be pasted.

Carbon fiber reinforcement plan and design

The construction plan is: plastering layer cleaning, base polishing, primer brushing, leveling treatment, brushing and pasting resin, and pasting carbon fiber cloth.

(1) The reinforcement of the wrapped angle steel is the same as the reinforcement of the roof truss: crack sealing treatment; stick carbon fiber cloth at the bottom of the beam. The amount of carbon fiber cloth is determined by increasing the bending capacity of the beam by 30%.

(2) According to the inspection data provided by the monitoring report, after analyzing and comparing multiple schemes, it is finally decided to adopt comprehensive reinforcement measures for the load-bearing walls with cracks and walls with cracks greater than 1.5mm in width.

Reinforcement construction and technical measures

The construction sequence of the comprehensive reinforcement of the concrete structure and the wall is: base treatment-chemical grouting for cracks-carbon fiber cloth on the wall-protective layer. .

Effect analysis of carbon fiber reinforcement

Due to the repeatability of temperature cracks in brick walls, it is difficult to deal with temperature cracks, and improper handling can easily cause secondary cracks. In this project, the cracks are sealed by chemical grouting to restore the integrity of the cracked wall, and then a comprehensive reinforcement such as carbon fiber cloth is applied. After the reinforcement was completed, after a winter and summer observation, no new cracks were found in the wall.

Conclusion

The use of carbon fiber composite materials to repair and strengthen the building has achieved good results, and can fully reflect the obvious advantages of this new technology compared to ordinary reinforcement methods. Such as high strength, super waterproof, anti-corrosion characteristics, simple construction, short reinforcement period, not restricted by structural shape, carbon fiber can be pasted on any curved surface, etc., which has good application prospects.