1. Introduction
The advancement of engineering materials and the discovery of new materials are the premise and motivation for the development of civil engineering. The emergence and application of carbon fiber materials have brought the research on reinforcement and reinforcement technology in civil engineering to a higher level. Carbon fiber cloth is a new type of building material, which is widely used because of its light weight, corrosion resistance, thin sheet and high tensile strength. The reinforcement method of carbon fiber cloth is also regarded as the reinforcement method of girder bridges to improve the bearing capacity, especially when the height is limited, and the construction process is relatively simple.
The carbon fiber cloth reinforcement and repair structure technology is to use the resin bonding material to paste the carbon fiber cloth on the concrete surface to achieve the purpose of strengthening and reinforcing the structure and components. The research of carbon fiber material (CFRP) for reinforcement and repair of concrete structures began in the 1980s in developed countries such as the United States and Japan, and my country started very late. Awarded with the 4th Academic Conference of Accreditation. Now the construction technology of carbon fiber cloth reinforced bridge concrete structure is compiled into a construction method.
2. Features of construction method
2.1 The carbon fiber cloth has high strength and good effect.
2.2 After reinforcement, the corrosion resistance and durability of the structure can be greatly improved.
2.3 The dead weight is light, and after reinforcement and repair, the dead weight of the original structure and the size of the original components are basically not increased. Good flexibility, easy to cut, and a wide range of applications.
2.4 The construction is simple (no need for large construction agencies and turnover materials), high work efficiency, no need for on-site fixed facilities, less construction site occupation, easy operation, and good economy.
2.5 The construction period is short. Therefore, the carbon fiber structure reinforcement technology has produced a great effect in the reinforcement of concrete structures.
3. Scope of application
3.1 It is suitable for reinforcement and repair of various structural types and various structural parts, such as beams, slabs, columns, roof trusses, piers, bridges, cylinders, shells and other structures. It is widely used in various types and shapes of concrete structures without changing the shape of the structure and without affecting the appearance of the structure.
3.2 The strength grade of base concrete shall not be lower than C15.
4. Process principle
The reinforcement mechanism is to bond the carbon fiber cloth to the surface of the concrete member with a high-performance epoxy adhesive, and use the good tensile strength of the carbon fiber material to achieve the purpose of enhancing the bearing capacity and stiffness of the member. It is difficult for the carbon fiber filaments of the carbon fiber cloth to work together completely. When bearing a lower load, a part of the carbon fiber filaments with higher stress levels first reach their tensile strength and exit the working state, and so on, the carbon fiber filaments gradually break until overall destruction. After using the binder, the carbon fiber filaments can work together well, which greatly improves the tensile strength of the carbon fiber cloth. Therefore, the carbon fiber reinforcement must first make the carbon fiber filaments in the carbon fiber cloth work together. Reinforcement plays a key role, it not only ensures that the carbon fiber filaments work together, but also ensures that the carbon fiber cloth and the structure work together to achieve the purpose of reinforcement.
5. Construction process and key points of operation
5.1 Construction process flow
construction process
5.2 Operation points
5.2.1 Reinforcement design scheme of beam bottom pasted carbon fiber cloth
According to the actual situation, the bottom of the beam is reinforced with carbon fiber cloth. The carbon fiber cloth is pasted under the beam rib, the single-layer carbon fiber cloth with a width of 25cm and a double-layer carbon fiber cloth with a width of 50cm are arranged under the rib of the hollow slab, and the double-layer carbon fiber cloth with a width of 50cm is arranged under the rib of the box girder. The carbon fiber cloth material is selected from the small tow polyacrylonitrile base of not more than 12k (1k=1000), and the fiber mass per unit area of the single-layer carbon fiber cloth material is 300g/m2.
The layout of the cross section of the hollow board pasted with carbon fiber cloth
Cross-sectional layout of carbon fiber cloth pasted at the bottom of box girder beams
5.2.3 Concrete Surface Treatment
(1) Draw a line on the concrete surface to determine the position to paste the carbon fiber cloth.
(2) Remove the stucco layer in this range, remove the peeling, loose, honeycomb and other inferior concrete on the surface of the structure, and expose the concrete structure layer. The raised part of the concrete surface should be chiseled to make it as smooth as possible. If necessary, the surface can be repaired with repairing materials. smooth.
(3) The corners should be chamfered and ground into an arc shape, and the radius of the arc should not be less than 20mm.
(4) The surface of the pasted concrete is polished and smoothed, and impurities such as surface laitance, loose objects and oil stains are removed, until the new concrete surface is exposed.
(5) Use acetone or industrial alcohol to clean the surface of the concrete, requiring no dust, no oil, and keeping it clean and dry.
concrete surface treatment
5.2.4 Apply primer
(1) Prepare the bottom resin glue. According to the concentration of the ambient temperature control, the concentration of the primer should not be large.
(2) Apply the primer on the concrete surface, and apply it repeatedly with a brush and a rubber scraper, so that the primer can be filled evenly.
Adhere to the concrete surface in parts and immerse in the concrete.
5.2.5 Leveling
(1) Prepare the bottom resin glue, and stir it thoroughly and evenly.
(2) After the bottom resin glue is dried, repair and level the concave part of the concrete surface with leveling glue. There should be no corners.
(3) Use leveling glue to repair the corner into a smooth arc with a radius of not less than 20mm.
(4) After the leveling glue is dried, proceed to the next step.
5.2.6 Paste carbon fiber cloth
(1) Cut the carbon fiber cloth according to the structural size. In order to facilitate pasting, the cut carbon fiber cloth should be rolled on a small round stick or cylinder and numbered for use. During the cutting and rolling process, the surface of the carbon fiber cloth should be kept free of dust and debris.
(2) Preparation of impregnating glue: Determine the amount of impregnating glue required according to the amount of carbon fiber to be pasted, and uniformly stir the two components A and B according to the proportion. The glue mixed each time should be used at the same time. It cannot be used after the time is exceeded. The amount of glue mixed each time should not exceed 2 kg.
(3) Apply the prepared impregnating glue evenly on the surface of the structure with a brush, and then lay the carbon fiber surface evenly on the impregnating glue layer. Use a special rubber roller or a rubber scraper to roll or scrape hard along the fiber direction. Care should be taken not to roll and scrape back and forth. Roll and scrape in one direction to remove air bubbles and excess glue, so that the impregnated glue Fully penetrate the carbon fiber cloth and bond firmly to the concrete surface. The carbon fiber cloth should not be damaged during rolling and scraping.
Apply bottom surface glue and paste carbon fiber cloth
5.2.7 Applying impregnating glue
Apply the impregnating glue evenly on the surface of the carbon fiber cloth again, and roll and smooth it with a roller or a rubber scraper, so that the impregnating glue should fully penetrate the carbon fiber cloth.
5.2.8 Curing and curing
(1) After carbon fiber cloth reinforcement construction, it should be prevented from rain or moisture, and attention should be paid to protect the construction surface from hard objects.
(2) Under normal circumstances, it is cured and cured at room temperature. When the ambient temperature is kept above 20 °C, it will be cured in 24 hours, with a certain strength, and can be stressed for 3 to 5 days. 15 days before the force can be used. If necessary, artificial heating can also be adopted to keep the temperature at 15℃~20℃. Generally, infrared lamps are used for heating.
Carbon fiber cloth secondary squeegee
Curing and curing
5.2.9 Construction precautions for pasting carbon fiber cloth
(1) Carbon fiber composite materials are conductive materials, and should be kept away from electrical equipment and power sources as far as possible.
(2) The bending of the carbon fiber cloth should be avoided during use.
(3) The raw materials of carbon fiber cloth supporting resin glue should be sealed and stored, away from fire sources, and avoid direct sunlight.
(4) The preparation and use site of resin glue should be well ventilated.
(5) On-site construction personnel should take certain labor protection measures.
(6) On-site construction electrical appliances and lighting must be safe and reliable.
6. Materials
6.1 Material dosage
Materials used in engineering
The carbon fiber material used for the reinforcement of this bridge is selected from small tow polyacrylonitrile-based (PAN-based fiber) not greater than 12k (1k=1000), and large tow fibers are not allowed.
The main mechanical properties of carbon fiber composites are as follows:
Main mechanical index
Carbon fiber sheets meet the requirements of high-strength grade I sheets, with a width of 100mm and a thickness of 1.2mm, and the measured value of the fiber volume content must be higher than 70%.
The fiber mass per unit area of the single-layer carbon fiber cloth is 300g/m2.
7. Benefit Analysis
7.1 Economic Benefit Analysis
Due to the fast construction, the construction period can be eased, the reinforcement materials can be saved, and large-scale mechanical construction is not required, which saves costs and has high economic benefits.
7.2 Social Benefit Analysis
Carbon fiber reinforcement does not require unloading of the structure, does not need to interrupt road traffic for bridge structures, and does not affect the reinforcement effect. It is especially beneficial for highways and main traffic arterial roads, which can completely avoid the economic loss caused by interruption of traffic. At the same time, the reinforcement method that does not interrupt the traffic is adopted, which also avoids the inconvenience of detours for people's daily travel, and creates good social benefits.