The two housing collapse incidents in Fenghua and Shangmian Hongqiao in Zhejiang Province have aroused widespread concern about the identification and reinforcement of old houses. According to incomplete statistics, my country’s existing buildings of nearly 20 billion m2 have entered the "middle-aged age". Among these buildings, quite a few have problems with residential performance, such as high energy consumption, poor use performance, incomplete functions, etc. Some buildings have safety hazards, such as poor seismic performance, defective structures, aging and unsafe components.

Scientifically and objectively evaluate and appraise the reliability of existing buildings. According to the evaluation and appraisal results, effective measures are taken to strengthen and repair the building structure to achieve the purpose of enhancing structural functions, prolonging service life, and meeting development needs, which is in line with my country's sustainable development strategy. Due to various reasons, there is a large stock of existing barracks that have problems but are still functioning. It is neither realistic nor feasible to decommission or demolish such buildings. Existing barracks with problems have been identified, and most of them can continue to function through reinforcement, transformation, and reinforcement. There are many methods of reinforcement, reinforcement and repair. Carbon fiber sheet reinforcement is one of them. It is a new type of technology that uses externally bonded high-performance composite materials to reinforce concrete structures. Because it can effectively enhance the bearing capacity and rigidity of the concrete components, it has simple construction, is basically not restricted by the shape of the reinforced component, basically does not change the original shape of the structural component, and can quickly restore the use function of the existing building . It is often used in the reinforcement and repair of military barracks. 

Glue the high-performance epoxy resin structural adhesive to the surface of the concrete member with a high-performance carbon fiber sheet and combine the carbon fiber with the concrete member. It can be regarded as adding steel bars in the concrete without changing the original structure shape. Make full use of the light weight, tensile strength and elastic modulus of carbon fiber to improve the bearing capacity of concrete structural members such as bending and shearing.

The basic principles of reinforcing and repairing structural concrete with carbon fiber sheets mainly include three aspects. The first is carbon fiber materials. Carbon fiber materials have extremely high tensile strength, which is 8-10 times that of HRB400 steel bars commonly used in construction, and also have relatively high elastic modulus, which is equivalent to steel bars. The second is the high-performance epoxy resin structural adhesive as a binder, which can not only wrap and bond the carbon fiber, make the fibers in the carbon fiber sheet work together, but also firmly bond the sheet to the surface of the reinforced concrete member. The third is that the carbon fiber sheet and the reinforced component share the load. The three aspects complement each other to achieve the improvement of the bearing capacity and rigidity of the members, and to achieve the purpose of reinforcement.

Based on the basic principles of carbon fiber sheet reinforcement of structural concrete members, in the process of carbon fiber sheet reinforcement, reinforcement, and repair of structural concrete, the following six aspects should be paid special attention.

1 Pay attention to the inspection of the original structure concrete

Before the carbon fiber sheet is used to reinforce the concrete structure, a qualified testing and appraisal agency shall inspect and appraise the original structure and evaluate the reliability of the structure and its components. Pre-detection of the original structure of the concrete can determine the inapplicability of using carbon fiber sheets to reinforce the concrete structure, effectively avoiding the blindness of structural reinforcement. Before reinforcement, the original structure concrete strength and steel reinforcement corrosion status must be tested, and the actual concrete strength, steel and steel reinforcement corrosion degree test reports must be issued to provide the basis for the reinforcement design check calculation and construction plan confirmation.

2 Pay attention to reviewing design and construction technical plans

Because the carbon fiber sheet reinforcement and repairing concrete structure technology is a new type of structural reinforcement technology, it has a particularity different from other methods. Before reinforcement, a qualified and experienced design unit must be familiar with reinforcement work for special design. The most significant mechanical property of carbon fiber sheet is its extremely high tensile strength. The basic requirement of the design should be to make the carbon fiber sheet bear tensile force. It is coordinated with the deformation of the concrete and bears the force together to give full play to the mechanical properties of carbon fiber at the same time. It is also necessary to carry out the ultimate state calculation of the bearing capacity and the check calculation of the normal use limit state in accordance with the current national standards, comprehensively consider the different reinforcement objects and structural requirements, and come up with a targeted design plan. The unit undertaking the construction should also have professional qualifications and be able to formulate a complete construction technical plan based on the reinforcement plan to ensure the effective implementation of the reinforcement and repair work. The reinforcement construction work has strong technical requirements and must be carried out in strict accordance with the construction procedures.

3 Pay attention to the sampling re-inspection of raw materials

The quality of material shaking directly affects the quality of reinforcement. Strictly controlling the quality of incoming raw materials is the basis for determining the success or failure of reinforcement and restoration work. After entering the field, all kinds of materials shall be subject to necessary random inspection and re-inspection according to their main technical indicators. The tensile strength, elastic modulus, elongation, and quality of carbon fiber materials are mandatory items. In addition to the positive tensile bond strength, the main testing indicators of impregnated resin or bonding resin should also test tensile shear strength, tensile strength, compressive strength, bending strength, elastic modulus, elongation and other items. Epoxy resin is an organic substance and has certain durability restrictions. If necessary, durability inspection should be carried out according to the subsequent service life of the structure and use environmental conditions.

4 Pay attention to the process control of the construction process

Ensuring the bonding quality of carbon fiber sheets is the most important and important task of reinforcement construction. Strictly controlling the construction process is the fundamental way to ensure the construction quality. Different control measures should be formulated according to different process links.

5 Pay attention to compatibility testing

The close combination of the carbon fiber sheet and the reinforced concrete member is a prerequisite for exerting the superior characteristics of the carbon fiber sheet. The bonding strength of the two is the basis for achieving the reinforcement goal, and the compatibility between the reinforcing material and the reinforced member is one of the key factors affecting the bonding strength. The compatibility mentioned here includes two aspects, one is the compatibility between the materials, and the other is the compatibility between the bonded materials and the concrete to be reinforced. No matter how good the quality of the material itself is, if the compatibility is not good, the bonding quality cannot be guaranteed. The compatibility between materials mainly exists between the carbon fiber sheet and the matching resin-based bonding material. The supporting resins mainly include bonding materials such as bottom resin, leveling resin, impregnating resin or bonding resin. The products of the same manufacturer are generally used during the reinforcement construction, and the mutual compatibility has sufficient conditions to be guaranteed. Due to the wide variety of carbon fiber sheets and resin-based bonding materials, the raw materials and processing techniques used by manufacturers in different origins are also different. The technical performance indicators of materials of the same type but different brands will vary. The combination of carbon fiber sheet and resin-based bonding material may cause poor compatibility and incompatibility. Therefore, it is necessary to verify the compatibility between the two through testing. The strength level and composition of the reinforced concrete The vibrations are not the same, and the concrete components of different regions are clearly different. The compatibility of the bonding material with the concrete of the reinforced structure should also be verified by testing.

6 Pay attention to on-site inspection of reinforcement construction quality

To determine the construction quality level of the reinforcement project, in addition to the inspection and acceptance of each process, on-site inspection should also be carried out, and the bonding quality and the actual bonding strength of the construction site should be inspected. The inspection and test results are used as the basis for judgment. To give play to the superior mechanical properties of carbon fiber sheet, it is necessary to rely on the reliable and firm bonding of carbon fiber sheet to the surface of structural concrete. The required bonding quality is the fundamental guarantee for the joint work of carbon fiber sheet and reinforced concrete components.

Conclusion

Using carbon fiber sheets to reinforce the concrete structure technology and grasping the above-mentioned links, it has achieved success in many existing building reinforcement projects, fully meeting the requirements of use, and effectively extending the subsequent use period of the house.