There are mainly two reinforcement schemes in the field of CFRP reinforcement of concrete columns.

(1) Non-prestressed CFRP reinforced columns;

(2) Prestressed CFRP reinforced columns.

1 Non-prestressed CFRP reinforcement column technology

The non-prestressed CFRP reinforcement column technology is the external paste CFRP reinforcement method, which is generally suitable for concrete column reinforcement, earthquake resistance and crack resistance. The reinforcement method is mainly to wrap the carbon fiber cloth on the weak part of the component, and apply epoxy resin glue to make the carbon fiber cloth firmly bond to the outer surface of the component, form a whole with the component, and bear the force together. Before wrapping the carbon fiber cloth, the surface treatment of the components is required to avoid sharp edges and corners, so as to prevent the stress concentration and cause the carbon fiber cloth to break. And the reinforcement effect is related to the wrapping method, paste thickness, fiber content and so on.

2 Prestressed CFRP reinforcement column technology

In engineering, the method of strengthening concrete columns with CFRP is the sticking method, but a large number of tests show that the carbon fiber cloth under the sticking method can only play a restraining role when the compression member is sufficiently laterally deformed. This defect can be overcome by applying prestress to the carbon fiber material, and the passive constraint can be changed into an active constraint to give full play to the high-strength performance of the carbon fiber material.

For prestressed CFRP reinforcement column technology, there are three main methods of prestressing at home and abroad:

(1) Self-locking anchor tensioning device;

(2) Tensioning device for prestressed carbon fiber cloth to reinforce column structure;

(3) The carbon fiber pipe is injected into the expanded cement mortar.

Self-locking anchor tensioning device is used to realize prestressed carbon fiber cloth column reinforcement. This kind of tensioning device is easy to construct and hardly affects the appearance of the reinforced column. After directly applying glue on the reinforced column, the carbon fiber cloth is wrapped and locked with a self-locking anchor. By tightening the nut, the carbon fiber cloth is tightened to one end at the same time to achieve the effect of prestressing. The disadvantage is that the method of applying prestress is to manually tighten the nut, and the pretension force applied to the carbon fiber cloth is not large.

The tensioning device used to reinforce the column structure with prestressed carbon fiber cloth is another prestressing technique. The device is developed for carbon fiber cloth, and the advantage is that it can apply greater prestress, and after the glue is hardened, the tensioning device can be removed and used in sequence. The disadvantage is that the structure of the device is complicated, the construction is inconvenient, and the use space is occupied when the tension device is not removed.

The carbon fiber tube injection into the expansion material is a unique way of applying prestressing in foreign countries. The core of the reinforcement method is to inject expansion material into the carbon fiber pipe to achieve the effect of applying prestress.

The above studies on CFRP-reinforced concrete columns are summarized as follows:

(1) Both non-prestressed CFRP reinforcement and prestressed CFRP reinforcement can improve the bearing capacity, ductility and energy dissipation performance of the column. However, the reinforcement effect of prestressed CFRP is better than that of non-prestressed CFRP, and with the increase of the tension force, the difference between the reinforcement effect of the two is more obvious.

(2) The non-prestressed CFRP reinforcement technology has matured and has been put into practical use in the project, and it is more used in the reinforcement and repair of the column bearing capacity in the building structure.