Reinforced Concrete Bridge

1 Project Overview

Construction of the Yunnan Jishi Expressway started in December 1999 and opened to traffic in November 2004. So far, the Jishi Expressway has been in operation for about 10 years, and the entire line has not undergone major repairs.

2 Disease situation

With the continuous development of the local economy, the traffic pressure is increasing day by day, especially the increase in heavy and overloaded vehicles, resulting in a decline in the carrying capacity and traffic capacity of some bridges on the expressway. Some components on the bridge have also been damaged to varying degrees, so some of them need to be repaired and reinforced.

3 Reinforcement plan

Difficulties of the project:

One is that the bridge span is relatively large, with a span of 40m and a single carbon fiber laminate length of 35m.

Second, the tensile stress value is large, the single tensile stress is 1200MPa, and the tensile force value is 24t.

Paste the CFPP prestressed carbon fiber laminate at the bottom of the beam with a spacing of 30 cm and 12 horizontally arranged. The size of the carbon plate is 35000mmx100mmx2.0mm, the ultimate tensile stress is greater than or equal to 2400kN, and the ultimate tensile strength is 480kN. The tensile stress of this project is 1200MPa and the tensile force is 240kN.

The continuous beam reinforcement project of Jishi Expressway started in September 2015 and has been completed. After careful structural inspection and bearing test, it meets the required bearing requirements and is in good condition.

4 Construction technology of reinforcing carbon fiber laminate

4.1 Substrate treatment

In order to strengthen the effect of the bridge reinforcement project and realize the improvement of the effective utilization rate of carbon fiber laminate, the first thing to be done is the substrate treatment. The damaged parts of the bridge should be repaired before the start of the reinforcement project. Carbonization and damaged parts should be removed, gaps should be repaired and some corroded steel bars should be cleaned up to make the bridge structure more complete. Polish the damaged and protruding parts to make the surface smooth. Use a grinder to polish the corners. The chamfer radius should be greater than 30mm to make the surface clean and tidy. After a period of time, when the bridge deck is completely dry and meets the construction requirements, the subsequent reinforcement process can be carried out.

4.2 Apply primer

The process of applying primer is particularly important in bridge reinforcement construction. Through this process, the coating can penetrate into the bridge structure, which provides convenience for the subsequent pasting of the carbon fiber laminate, and can also strengthen the curing effect. It is worth noting that the preparation of coatings should be carried out on the premise of actual construction needs, and the mixing ratio of main agent and curing agent should be determined in accordance with the specific requirements of painting. Stirring must be sufficient to ensure that the paint is in a uniformly mixed state. In view of the characteristics of easy curing of the primer coating, the coating should be applied immediately after the preparation is completed and completed as soon as possible to avoid this problem.

4.3 Paste carbon fiber laminate

Determine the amount of carbon fiber laminate used according to the size of the bridge reinforcement area. First cut the carbon fiber laminate. Under normal circumstances, in order to ensure the ding effect, the length of the carbon fiber laminate should be less than 2m. Touch and confirm the dryness of the primer on the construction surface with your fingers. Put the epoxy resin main agent and curing agent in the mixing barrel according to the specified mixing ratio and mix them evenly for about 2 minutes to ensure they are fully mixed. Use a brush roller to apply epoxy resin evenly on the primer. The roughness of the construction surface determines the amount of brushing. After the carbon fiber laminate is pasted on the resin coating surface, use a brush roller and a squeegee to push it flat along the fiber direction to achieve the requirements of removing excess air bubbles and impregnating the resin. In the fiber length direction, there should be at least 10cm of lap length. On the contrary, the short direction does not need to stay. After the carbon fiber laminate is pasted, it should be left for 30 minutes. If during this period of time there is a situation such as floating or disconnection, it should be flattened or repaired with a roller or a squeegee in time to ensure the best construction effect. It is worth noting that when pasting the carbon fiber laminate, the construction should be carried out in an environment with unobstructed air and no fire and smoke, and the construction personnel must wear protective equipment during the construction.

4.4 Surface coating

For structures or components with appearance decoration requirements, the surface of the carbon fiber after the paste can be painted with epoxy-based paint or conventional paint after sandblasting

5 Conclusion

Carbon fiber laminate has light weight, high tensile strength and good ductility. It can repair various structures without affecting the appearance and beauty of the bridge structure. Carbon fiber laminate reinforcement construction is simple and efficient. Even if the market price of carbon fiber laminate is higher than other materials, the overall cost of other materials is actually reduced to a large extent. It avoids the complicated procedures such as erecting form, supporting, pouring concrete, assembling and disassembling fixtures, curing, and dismantling forms required by traditional measures such as concrete reinforcement and steel plate reinforcement. And it does not take up too much space, even if it is working at high altitude, only a simple working platform is required. Therefore, the comprehensive cost of using carbon fiber laminate to strengthen the bridge is lower than the traditional repair method. In addition, the carbon fiber laminate reinforcement has good durability and corrosion resistance, and even no anti-corrosion treatment is required. However, steel plate reinforcement cannot eliminate the process of corrosion and rust prevention. Because the carbon fiber laminate reinforcement project reduces the occupied space, shortens the construction period, and the construction is simple and efficient, it can greatly reduce the impact of the reinforcement construction on the surrounding environment of the site. Carbon fiber laminate reinforcement technology meets the needs of bridge reinforcement projects and has broad application prospects.