1 Project Overview

A certain bridge is located in a part of K11O and was built in the early 1990s. At that time, the design standard was the first-class highway of the Ministry of Transport, and the road load standard was: 10O for hanging and 20 for steam. The whole bridge was composed of two-way lanes, and finally two half-span bridges were formed with separate lanes in the middle of the bridge. The length and width of the bridge are 91m and 23.5m, respectively, and the hollow slab beam made of reinforced concrete with L=13.0m is used as the upper structure of the bridge. The lower structure is a double-column bored pile pier. Except for the two abutments which are 1.3m in diameter, the remaining piers are 1.2m.

2 Bridge status

Through careful inspection of the bridge, more serious problems appeared in the deck pavement and load-bearing member slab girder of the bridge structure. The diseases were mainly reflected in the following aspects:

(1) There are many longitudinal cracks in the slab beam, and the internal steel bars are severely corroded;

(2) Corrosion and mildew of concrete of some slab beams are more serious, and the corresponding rebound strength is obviously low;

(3) There are many net-like cracks on the bridge deck, and the cracks formed are more obvious;

(4) The drain hole on the bridge is blocked and cannot drain effectively;

(5) The guardrail of the bridge has been severely weathered, with concrete peeling off and steel rusting.

3 Selection and principle of maintenance and reinforcement plan

Now a brief introduction and comparison of the commonly used bridge repair and reinforcement methods.

3.1 Use reinforced concrete for outsourcing

Reinforced concrete is used for outsourcing on the original bridge to form a new soil surface layer, which increases the construction surface of the bridge body, thereby improving the rigidity, dynamic performance and bearing capacity of the bridge body. This kind of construction method is relatively simple, so that the ductility, bearing capacity and stiffness of the bridge can be greatly and effectively improved; the disadvantage is that it requires a longer construction period.

3.2 Reinforce with adhesive

The steel plate and the bridge are pasted together with an adhesive to increase the bearing capacity of the bridge. The advantage of this reinforcement method is quick and convenient construction, and it has no major impact on the bridge. The disadvantage is that the cost of bridge maintenance is too high, and the adhesive has strict requirements on the environment, and the ambient temperature it uses is less than 60°C.

3 3 Reinforcing bars outside the bridge

In order to effectively improve the ductility and bearing capacity of the bridge structure, the original bridge structure can be planted with reinforcing bars and tensile prestressed tendons can be provided. The advantage of this reinforcement method is that construction can be carried out under normal use, and the construction period is short and convenient. The disadvantage is that higher maintenance costs are required, and the higher requirements for the original bridge's diaphragms and webs are good.

3.4 Reinforce with carbon fiber

The carbon fiber cloth is glued to the bridge with epoxy resin adhesive and pasted along the direction of the force, finally forming a new composite structure. The original reinforced concrete and carbon fiber jointly form the bearing surface, so that the bridge structure can increase the shear and bending resistance. The advantage of this reinforcement method is that the cross-sectional size and structural weight do not increase. At the same time, the construction is more convenient when the headroom size does not change, and the construction can enhance the fatigue resistance, durability and corrosion resistance of the bridge without damaging the original structure. The disadvantage is that the ratio between the formed elastic modulus and the strength is low. If the temperature exceeds 60°C, the epoxy resin will soften.

Combining the degree of disease of the slab beam of this project and the introduction of the above several maintenance and reinforcement schemes, and considering that Ningtong Highway is one of the main roads in our province, the traffic flow is large, and the closed traffic for a long time will increase the detour distance. The impact is greater, so it was decided to adopt two schemes of replacing the slab beam and sticking carbon fiber cloth for reinforcement and maintenance. Since the prefabrication of the slab beam has matured, it will not be described in detail here.

4 The principle of carbon fiber cloth in bridge reinforcement

Carbon fiber material has good mechanical properties in the application of building structure, and it can be dozens of times stronger than building steel. Adhesive bonding can effectively concentrate the common strength of carbon fiber threads and increase the tensile strength of carbon fiber cloth. Therefore, in the reinforcement process using carbon fiber cloth, the carbon fiber filaments must form a unified stress surface on the carbon fiber cloth. At this time, the binder plays an extremely important role. It can not only make the carbon fiber filaments produce collective The force can also make the bridge structure and the carbon fiber cloth bear the force together, and finally realize the bridge reinforcement.

5 Key points of carbon fiber cloth construction

(1) The corner radius of the pontic structure should be greater than or equal to 20mm to reduce the carbon fiber stress at the corner. After multi-faceted practical experience, even through this treatment, the carbon fiber cloth may still be damaged at the corner.

(2) Repairing the surface of concrete components is very important, and it has a great influence on the performance of carbon fiber cloth.

(3) Carbon fiber cloth material can conduct electricity, so avoid contact with electrical equipment during construction, and take corresponding protective measures during construction.

(4) The carbon fiber cloth should be adhered firmly. If it is peeled off, it will not be able to play a strong role in reinforcement, and it will not play its good performance.

(5) When checking the quality of the carbon fiber cloth, you can use tapping and hand pressure to check the surface of the carbon fiber cloth to ensure that the dense area is >95%; if the bonding length is not enough, the bonding should overlap 300mm.

(6) During the construction process, the resin ratio corresponding to the carbon fiber cloth construction should be strictly implemented in accordance with the requirements, and the dipping should be soaked in the carbon fiber cloth, and the glue should be evenly brushed on the concrete surface. The construction personnel should be fully equipped and the carbon fiber cloth construction time Be in control.

(7) The best construction time for carbon fiber cloth should be greater than 5°C. In a low temperature environment, heat preservation is required, and attention should be paid to the large difference between the temperature of the structural material and the ambient temperature to avoid loopholes and ensure the construction environment Humidity of 85% or less.

(8) Some supporting materials of related carbon fiber cloth should be sealed and stored to prevent light and fire. The construction site should be well ventilated to ensure the safe configuration of resin.

(9) Construction personnel should pay attention to safety and take protective measures in advance.

6 Carbon fiber cloth reinforcement advantages

(1) High tensile strength: The tensile strength of carbon fiber cloth is generally more than 3000Mpa, which is 10 times that of ordinary steel. After it is pasted with epoxy resin and reinforced concrete components, the reinforcement effect is obvious.

(2) The construction speed is fast and simple: carbon fiber cloth is a very light material. During the construction process, large construction equipment is basically not involved, and the operation is relatively easy. However, in the case of repair and reinforcement of cross-line bridges and river-crossing bridges in special sections, special construction plans need to be drawn up for the erection and construction of supports to ensure construction safety.

(3) It is resistant to corrosion of acid, alkali and salt media and has good durability: carbon fiber cloth only uses supporting resin in the reinforcement process, so there is no rust, and it is resistant to acids and alkalis in natural environments. The anti-corrosion characteristics can be applied to the reinforcement of components in various working environments.

(4) The original structure is not changed, and the appearance is beautiful: According to the shape of the component, the carbon fiber cloth can be cut and pasted at will during the construction, and the weight and volume of the construction will not increase after the construction, and the decoration and fireproof materials can be painted on the outside.

(5) The dead weight is light, and the structural dead weight and cross-sectional size do not basically need to be increased; it is convenient to cut, and has good flexibility, which is more suitable.

(6) The cracks produced by the concrete structure can be effectively closed, which prolongs the service life of the concrete structure.

(7) Too short construction period.

7 Concluding remarks

The construction technology of carbon fiber cloth paste reinforcement can effectively strengthen the old bridge. This method is also widely recognized internationally, and it attaches great importance to this technology, and is also widely used. Practice has proved that its superiority is the development technology of my country's future old bridge reinforcement. After the application of this project, its characteristics of low weight, simple construction, and short construction period have been well reflected in the process of technical implementation. Due to the impact of construction period, traffic, simple structure and other conditions, the quality of maintenance and reinforcement of this project needs to be observed and monitored for two to three months or even longer. Through the collection and analysis of data, it is possible to accurately assess the effect of bridge repair and reinforcement and summarize experience, laying the foundation for the future use of this technology in the repair and reinforcement of long-span bridges or bridges with more complex structures in our province.