In modern construction engineering, carbon fiber cloth has gradually become a popular choice for structural reinforcement due to its excellent mechanical properties and construction convenience. Its appearance is light and thin, with a thickness of only 0.1 millimeters, which may raise questions: can such thin materials really be used to reinforce building structures? This article will provide a detailed analysis of the advantages of carbon fiber cloth.
Carbon fiber is divided into three categories based on its main raw materials: polyacrylonitrile (PAN) – based carbon fiber, asphalt (PITCH) – based carbon fiber, and adhesive (RAYON) – based carbon fiber. From the perspective of structural reinforcement performance requirements, only PAN based carbon fiber best meets the safety and durability requirements of load-bearing structures; The performance and quality of adhesive based carbon fiber are poor and cannot be used for reinforcing load-bearing structures; Asphalt based carbon fiber only has medium to high modulus filaments, which can be used for reinforcement applications that require high rigidity materials. However, such applications are rarely encountered in typical building structure reinforcement, and there is no practical experience in use in China. Therefore, polyacrylonitrile based (PAN based) carbon fiber must be selected as the carbon fiber material for structural reinforcement.
When using carbon fiber cloth for reinforcement, for important structures, it is necessary to use carbon fiber cloth woven with small fiber bundles of 12k or less, mainly because the tensile strength of small fiber bundles is very stable, the dispersion is very small, and their coefficient of variation is below 5%. Moreover, the adhesive is easy to infiltrate and penetrate, so its performance and quality can be effectively controlled during production and use; However, the coefficient of variation of large fiber bundles is over 15%, indicating poor reliability in experiments and trials, and therefore cannot be used as structural reinforcement materials.
The carbon fiber cloth used for structural reinforcement is a fabric made of polyacrylonitrile (PAN) – based carbon fiber filaments. Its tensile strength is about 10 times that of steel, but its density is only 1/4 of steel. The main characteristics of this material are:
1. High intensity:
The tensile strength of carbon fiber cloth can reach over 3400MPa, far higher than building materials such as steel bars and concrete. At the same time, its elastic modulus is more than twice that of steel, and it has strong elastic deformation ability.
The high tensile strength of fiber materials is due to their small diameter, which results in much fewer internal defects compared to block shaped materials. For example, the tensile strength of block glass is 40-100 MPa, while the standard tensile strength of glass fiber can reach over 2000 MPa, which is dozens of times that of block glass.
2. Lightweight:
The carbon fiber cloth used for structural reinforcement is 200g/㎡ and 300g/㎡, with corresponding thicknesses of 0.111mm and 0.167mm. It can significantly increase the structural bearing capacity and seismic performance without affecting the space and weight of the components after reinforcement.
3. Corrosion resistance:
Carbon fiber cloth used in construction projects can not only withstand the alkaline corrosion of cement, but is also very suitable for corrosive environments such as frequent salt damage and erosion. Its durability is also good, and it has a good waterproof effect, which can suppress the deterioration of concrete and the corrosion of steel bars. Concrete components reinforced with carbon fiber cloth have a longer service life.
4. Anti fatigue:
When loaded in the direction of carbon fiber, even at high stress levels, carbon fiber cloth remains insensitive to tensile fatigue damage. Compared with ordinary reinforced concrete, the fatigue resistance of concrete reinforced with carbon fiber cloth has been greatly improved. Experimental research has found that after a certain number of fatigue cycles, the strength and ductility indicators of concrete reinforced with carbon fiber cloth did not decrease compared to the control specimens that did not undergo fatigue cycles. After experiencing the same fatigue cyclic load, the static strength and ductility indicators of ordinary reinforced concrete specimens will decrease to varying degrees. This is mainly due to the excellent fatigue resistance of carbon fiber materials themselves. Therefore, when reinforcing structures subjected to repeated loads, considering the use of carbon fiber materials would have significant advantages.
5. Easy construction:
Carbon fiber cloth reinforcement construction is convenient, with most processes being manually operated without the need for special equipment, low technical difficulty, no welding process, and no noise. The required site space during construction is small, and it can reinforce various parts, shapes, and components in various environments of the structure. Carbon fiber cloth reinforcement can also be used for certain structural parts that are almost impossible to construct with traditional reinforcement methods. The construction quality is also easy to control, the workload is small, and the construction period is greatly shortened.
It is precisely because of these advantages of carbon fiber materials that carbon fiber reinforcement is widely used worldwide. In the early 1980s, carbon fiber cloth was widely used in structures with special performance requirements or severe chemical erosion. In 1981, Sweden’s Meier was the first to use bonded carbon fiber composite materials to strengthen the Ebach Bridge. Over the next decade, the technology of bonding carbon fiber fabrics to strengthen concrete structures has made rapid progress in countries such as Japan and the United States. In Japan, carbon fiber reinforcement is widely used in structures such as highway bridges, railway bridges, tunnels, docks, and building constructions. Especially after the Great Hanshin Earthquake, structures damaged after the earthquake were reinforced with carbon fiber cloth, and no serious damage occurred when they experienced the earthquake again. In the UK, carbon fiber materials are used on offshore oil platforms to resist the impact of various waves. In Italy, carbon fiber cloth is not only used for the reinforcement of industrial plants, exhibition halls, and road bridges, but also for the restoration and reinforcement of historical architectural heritage.
