Carbon Fiber Sheet Repairing

Project

The Jinhua Super Bridge is a double T-beam bridge built and put into operation at the end of 1993, and it was discovered by the Xiangfan Public Works Section during the maintenance of the bridge. Reinforced concrete beams fell off, the main reinforcement and stirrups were exposed, and the corrosion was serious. The inspection agency was commissioned to test the concrete beams of the bridge. The conclusions are as follows.

(1) The protective layer of the 12 and 16 m pre-tensioned prestressed beams meets the requirements. The thickness of the protective layer of the main reinforcement of the 8 m ordinary reinforced concrete beam is less than 3 cm required by the code at individual parts, and the minimum is only 1 cm. The thickness of the protective layer of the stirrups is locally less than 1.5 cm required by the code, and the stirrups are exposed in some places.

(2) The construction quality of 8 m reinforced concrete beams is poor, the concrete aggregate gradation is not good, and the sand and gravel content is too large, resulting in poor concrete compactness. The protective layer is easy to fall off in pieces, and the longitudinal bars and stirrups are exposed and corroded; on the other hand, because the concrete protective layer is locally thin, local steel bars are corroded seriously.

(3) Due to the general durability repair problem of 8m ordinary reinforced concrete beams, although the current bearing capacity of concrete beams still meets the requirements, if not treated in time, the corrosion of steel bars will increase, which will reduce the effective area of steel bars. The effective bonding capacity between steel bar and concrete is weakened. It will ultimately affect the carrying capacity of concrete beams and the safety of train operations.

In view of the serious diseases of the above bridges, reinforcement and repair of the Jinhua Bridge were arranged in 2004. Adopt a new technology of carbon fiber sheet (CFRP) and crack repair glue (modified epoxy resin structural adhesive).

Repair plan

(1) Chisel off the loose protective layer concrete to expose the corroded steel bars, and perform rust removal and anti-rust treatment on the steel bars.

(2) Repair and restore with repair mortar infiltrated into a certain proportion of interface agent.

(3) Cover the tension flange of the T-shaped beam with a layer of carbon fiber sheet for structural reinforcement and durability and anti-corrosion treatment to improve the bearing capacity of the beam.

(4) Apply glue on the exposed concrete surface where the carbon fiber sheet is pasted to enhance the compactness and durability of the concrete.

Construction process and process requirements

Inferior layer processing

Repair glue surface repair

Crack grouting construction

Carbon fiber sheet reinforcement

Paste beam waterproof fabric curtain

The effect of the project

1) After the repair and protection system is painted, the surface of the beam body is firm and clean, does not crack, and is firmly bonded to the concrete, which also effectively increases the density of the concrete. In particular, the repair agent has strong bonding power, and the waterproof fabric curtain and the beam body are also very firmly bonded. After the construction, no cracks have been found in the waterproof curtain.

(2) The use of repair glue, a modified epoxy resin structural adhesive, overcomes the shortcomings of epoxy resin that is brittle and poor in toughness. Its cohesiveness is also very strong, so that the carbon fiber sheet (CFRP) and the beam body are firmly bonded, and the beam body is formed as a whole to bear the force, which gives full play to the excellent mechanical properties of carbon fiber sheet. Thereby, the bearing capacity and bending stiffness of the beam can be improved, and the deflection can be reduced. By calculation, the bearing capacity can be increased by 20%. At the same time, it improves the stress state of the components, enhances the ductility of the components, reduces concrete cracks in the tension zone, delays concrete aging, and improves the durability of the structure.

(3) Carbon fiber sheet has excellent physical and mechanical properties, its tensile strength is 10-15 times higher than that of ordinary steel, and its elastic modulus is close to that of steel, making it very suitable for reinforcement and repair of reinforced concrete. The construction process is simple, easy for workers to master, and the construction efficiency is high and convenient. No need for large machinery, carbon fiber sheet can be cut arbitrarily, and can be widely used in various types and shapes of concrete structures. After reinforcement and repair, there is basically no increase in structural weight and overall dimensions. The carbon fiber sheet is soft, and it can be effectively pasted even if the reinforced surface is not flat enough. It is resistant to acid, alkali, salt and atmospheric corrosion, and does not require regular maintenance. This new technology has good economic and technical benefits, and the effect is obvious. It is better than the steel plate bonding reinforcement method and has popularization value.