FRP composite materials are widely used in the repair and reinforcement of concrete structures due to their low density, high tensile strength and excellent corrosion resistance. It is a composite of high-performance fiber cloth, high-strength binder and curing agent. The most commonly used fiber cloths are carbon fiber cloth and aramid fiber cloth.

Performance analysis and evaluation

1 Material performance comparison

Aramid fiber and carbon fiber, as a new type of non-metallic composite material in the field of structural reinforcement, have several characteristics: 1) High elastic modulus, high tensile strength; 2) Low density; 3) Good durability, corrosion resistance and aging resistance ; 4) High fatigue strength; 5) Anisotropy; 6) The stress-strain relationship is linear.

The strength of the above two fibers is the strength of the material itself, not the fiber cloth

Strength, the strength of specific fiber cloth is as follows:

1) Carbon fiber: 0.11mm, 0.167 mm and 0.333mm are commonly used specifications, with a strength of 3 600 MPa. Because carbon fiber is brittle failure, there is no sign before failure.

Trillion, so the safety reserve factor considered is generally 0.5 to 0.7, that is, the strength that can be exerted

There is 0.7×3 600=2520 MPa.

2) Aramid fiber: AK-40 and AK-60 are two commonly used specifications, the thicknesses are respectively

Are 0. 193 mm and 0. 286 mm, the strength is 2 060 MPa, due to the toughness of aramid fiber

Performance is particularly good, so its safety reserve coefficient is generally 0.75 to 0.95, that is, it can send

The volatility intensity is 0.85×2 060=1 751 MPa.

Therefore, the effective value of strength is that carbon fiber is larger than aramid fiber. However, the failure form of the component after carbon fiber reinforcement is brittle failure, which makes it more suitable for structures that bear long-term static loads. The aramid fiber has strong resistance to local impact (as can be seen from the early use of body armor), so it is more suitable for components that bear dynamic loads.

In addition, the reason why FRP material is used for reinforcement is mainly that after the fiber cloth is impregnated with resin, it can achieve a coordinated deformation through the good bonding ability between the resin and the concrete, and jointly bear the load. Since both aramid cloth and resin are organic materials, the bonding force between the two is very strong. When the resin is combined with the inorganic carbon fiber, the permeability is better than that of aramid fiber, and the construction period is shorter than that of aramid fiber, which reduces the overall cost accordingly.

2 Comparison of construction performance

Compared with aramid fiber cloth, carbon fiber cloth is more flexible. It can be cut into the required shape and size with scissors on site during construction, and it has extremely high adaptability to different shapes of components. Due to the light weight of carbon fiber cloth, no lifting equipment is required, and it can be completed manually by using small machines. It can also be constructed in a small space (10 cm). The construction speed is fast, the cycle is short, and the bonding quality is easy to guarantee. In addition, the surface of the fiber is easy to paint, which is well adapted to environmental requirements and can minimize repair marks.

3 Comparison of economic performance

Similar to carbon fiber cloth, the price of aramid fiber material is higher than that of traditional structural reinforcement materials, and its overall cost is also higher. The economy of carbon fiber is mainly reflected in the following aspects:

1) Less cost during transportation, storage, loading and unloading, processing and maintenance;

2) The construction does not require large-scale equipment and machinery, which reduces the cost of mechanical shifts and reduces the need for structural

Interference from normal use;

3) Due to the fast construction speed, the construction period is shortened and labor costs are saved;

4) Good durability, which reduces maintenance costs accordingly.

Judging from the existing engineering practice abroad, the comprehensive cost of carbon fiber reinforcement for large and medium-sized structures such as bridges is lower than the comprehensive cost of pasting steel plates, and the comprehensive performance is also better.

4 Comparison of applicability

Fiber reinforcement is widely used in almost every field of civil engineering such as bridges, subways, underground structures, industrial and civil buildings, water towers, pools, chimneys, etc. It basically covers the reinforcement of concrete under tension, compression, bending and shear. Carbon fiber cloth has high tensile strength and fatigue strength along the fiber direction, but low compressive and shear strength. Therefore, it is mainly suitable for the reinforcement of concrete structures under tension, especially for the reinforcement of beams. However, due to the brittleness of the damage, the safety factor must be fully considered when designing. Like carbon fiber materials, aramid fiber, which is also a composite material, has a low compressive strength, but its shear resistance is excellent, so it is very ideal to be used as a pier's shear resistance and seismic reinforcement.

5 Safety comparison

The key to whether the technical performance of FRP composites to strengthen concrete structures meets the requirements lies in whether the bonding between the fiber cloth and the concrete can be guaranteed. At present, under the specified design and construction methods, using qualified reinforced fiber composite materials to reinforce concrete structures can effectively improve the bearing capacity and stiffness of concrete components, and reduce the deflection of components, improve the ductility of components and limit the expansion of cracks, improve the seismic performance of the structure, thereby extending its service life.