The technology of reinforcing and repairing concrete structures with carbon fiber reinforced polymer is to paste the carbon fiber cloth on the surface of the concrete with a supporting adhesive to play the role of structural reinforcement and seismic reinforcement. It is widely used for the reinforcement of building beams, slabs, columns and walls, and can be used for the reinforcement of bridges, tunnels and other civil engineering. Crack treatment and grouting, combined with steel-bonded reinforcement treatment, enhances the stiffness of the roof truss upper chord, and has been widely used in the reinforcement and reconstruction of existing buildings. In addition to the similar advantages of pasting steel plates, it also has the advantages of corrosion resistance, moisture resistance, almost no increase in structural weight, durability, and low maintenance costs. However, special fire prevention treatment is required, which is suitable for concrete structural members and general structures with various stress properties.

Common problems of beam-slab bearing structure

The main reason for the lack of bearing capacity of beams, slabs and other flexural members in design is the inconsistent calculation of the force, or the calculation of load surge or miscalculation. Severe overloading may also lead to insufficient bearing capacity of beams and slabs, due to insufficient concrete strength during construction, or insufficient bending resistance of beams and slabs due to improper reinforcement. In addition, the foundation settlement caused some additional stress due to other reasons. When dealing with this stress, some inappropriate devices were used, which adversely affected the beams and plates. For example, adding thin web beams to the beam and plate when dealing with stress, although the effect of the stress can be balanced, and the dead weight is not increased much, but some thin web beams will appear oblique cracks, causing the beam and plate components to rust and the durability is greatly affected. In severe cases, the beams and slabs may break and affect the bearing capacity of the beams and slabs. Some of the reasons for the above situation are the insufficient length of uranium lap joints or the influence of load changes. The main purpose of load-bearing reinforcement of beams and slabs is to strengthen the strength, stability, rigidity and durability of components.

Reinforcement of beam and slab structure

There is a big difference in the force-bearing properties of the beam-slab structure that has been built and strengthened and the general structural beam-slab without reinforcement. One is that the reinforced structure is subjected to secondary treatment and secondary stress, and the structure has to be subjected to secondary stress on the basis of the original stress, and the original structure may be deformed and bent. In addition, the original load is not removed during reinforcement, which is equivalent to secondary compression, and the newly added part of the stress is different from the original structural load stress. When the two stresses reach their peak values at the same time, the destructive force has also reached the limit state. Therefore, the above major problems are faced when strengthening the beams and slabs. In addition, the overall work of strengthening the new and old parts is different, and there are big differences in the calculation of stress and structural treatment. Therefore, the reinforcement of beams and slabs is different from ordinary concrete structural engineering, so carbon fiber reinforcement technology should be introduced in the reinforcement to improve the reinforcement of concrete beams and slabs.

Process and characteristics of carbon fiber reinforcement

Scope of application

It is suitable for the reinforcement and repair of various structure types and various structural parts, such as beams, slabs, columns, roof trusses, piers, bridges, cylinders, shells and other structures. The strength grade of the base concrete is not lower than C15, and the carbon fiber cloth reinforcement technology has been successfully applied to various beam and slab reinforcement and maintenance in China.

In Haimen in 2014, after the Haimen Daxin Bridge tried to use glued steel plates to strengthen the bridge, the Haimen Linjiang Gate Bridge was repaired for the first time to use the method of sticking and wrapping carbon fiber cloth to strengthen the bridge. This is the first time in Haimen repairing and strengthening bridge construction technology. Carbon fiber reinforcement can quickly reinforce the bridge, prevent external moisture from entering the concrete cracks and cause corrosion to the steel bars, ensure the durability of the components, help improve the load-bearing capacity of the bridge, and will not affect the normal operation of the bridge during the reinforcement. The Linjiang sluice bridge invested 350,000. The highway department carried out a comprehensive repair of the existing diseases of the Linjiang sluice bridge. It added 4000kg of expansion joints to tie up the steel bars, and the bridge arch foot was pasted with 500 square meters of carbon fiber cloth and 500 square meters of polymer mortar. Through maintenance of trunk roads and bridges, various hidden safety hazards were eliminated in time, which effectively improved the technical status of trunk roads and bridges in Haimen, and effectively guaranteed the safety and smooth flow of trunk roads.

Carbon fiber reinforcement process

Deteriorated parts such as surface peeling, honeycomb, corrosion, etc. should be removed on the concrete surface, and the large area of inferior layer should be repaired with epoxy cement after removal. The surface of the concrete is smooth, and there is no dust, oil and other sundries on the surface. The protruding parts are ground flat, and the corners are more than 20 mm rounded. Treat the concrete surface with a blower or vacuum cleaner and keep it dry. If acetone wipes the absorbent cotton on the concrete surface, such as water leakage, water conduction, etc., the surface treatment of the reinforced structure will directly affect the quality of the reinforcement.When the primer is cured (the surface of the primer is dry to the touch), use a smoothing machine to smooth the bumps to prepare for the next process, and then apply the impregnating resin and stick the carbon fiber. Attention should be paid to ventilation and labor protection at the site.

Carbon fiber reinforcement features

Carbon fiber reinforcement is the use of carbon fiber cloth and structural glue to reinforce the components. The reinforcement damage morphology is bonded with carbon fiber sheets as follows:

(1) The tensile steel bar yields, and then the concrete is crushed under pressure, and the carbon fiber sheet has not yet reached the allowable tensile stress change requirement;

(2) The stress of the steel bar reaches yield, the carbon fiber has exceeded the allowable tensile strain, and has not exceeded the required strain value of the construction project, the tensile reaches the ultimate tensile stress, and the concrete in the compression zone is not crushed;

(3) The reinforcement of carbon fiber cloth is too large, the steel bar yields, and the concrete in the compression zone is crushed;

(4) In the normal part of the bearing capacity, the carbon fiber cloth and the concrete foundation surface will peel off.

Conclusion

The technology of reinforcing concrete structures with carbon fiber sheets is a hot application in modern civil engineering circles. Therefore, it is necessary to continuously improve all aspects of construction, and pay enough attention to the acceptance after construction. For the acceptance of carbon fiber reinforcement after construction, the general practice is to gently tap the surface of the carbon fiber cloth with a small hammer to determine the effect of back bonding for the quality of the bonding between the concrete. If the hollow bulge appears incomplete, it should be repaired with adhesive. For reinforced concrete structures and components, carbon fiber reinforcement technology is very ideal. In terms of ensuring the size and weight of the section and not increasing the difficulty of construction technology, the durability of materials and construction quality can meet the construction quality requirements. On the whole, its comprehensive economic and social benefits have achieved a double harvest, and it has a broad market prospect. In addition, there is also a large room for improvement in technology.