Engineering background

A residential area in Jingtang Port, a total of 7 buildings, with a brick-concrete structure, was built in 1999. For some reasons, construction was suspended after the main body was completed, and interior and exterior decoration was not done. Purchased by a development company in 2006, ready to continue construction.

The residential building in this community has been parked for 7 years and many engineering problems have occurred. Through visual inspection, rust spots on the bottom of the residential floor slab in this community can be seen everywhere, severe hollowing, most of the protective layer peeling off, and long cracks along the direction of the steel bars. Cracks in beams and slabs are caused by corrosion and expansion of steel bars. The component concrete is severely carbonized, the concrete is loose, and the steel retrofitting is severely corroded. Most of the steel bars at the bottom of the slab are exposed, and the retrofitting cross section is weakened, which endangers the safety of the structure and affects people's emotions. According to the design drawings and the corrosion situation of the concrete and steel bars on the site, the relevant quality inspection department decided that the project needs to be retrofitting before the construction can continue.

On-site investigation and test results:

(1) The strength of concrete can basically meet the design requirements, and the surface strength of concrete is smaller than that of the interior;

(2) The concrete cracks along the retrofitting are longitudinally connected;

(3) Serious peeling of concrete surface;

(4) The corrosion of steel bars is very serious, and the cross-section of the steel bars in the tension zone is damaged, and some have reached 50%.

Structural retrofitting plan

Looking at the existing international structural retrofitting and renovation technology, it can be roughly divided into 6 categories: (1) Enlarged section method; (2) Encased steel retrofitting method; (3) Bonded steel method; (4) Prestressed retrofitting method (5) retrofitting method by changing the way of structural force transmission; (6) Carbon fiber retrofitting method. Practice has proved that the carbon fiber retrofitting method has the advantages of high strength, high modulus, corrosion resistance, fatigue resistance, easy processing, light weight, and easy manual operation. Carbon fiber retrofitting is considered to be the most promising method of structural retrofitting due to its outstanding material mechanical properties and high efficiency.

Corrosion of the steel bar causes the reduction of the cross-sectional area of the steel bar, the strength of the steel bar decreases, and the loss of the bond between the steel bar and the concrete causes the strength to decrease. When strengthening, the number of longitudinal carbon fiber cloth should be calculated according to the degree of structural corrosion to improve the bearing capacity.

Carbon fiber retrofitting material

Carbon fiber sheet and adhesive produced by Shanghai Horse Construction Co., Ltd.

HM-20 carbon fiber sheet

HM-180C3P carbon fiber adhesive

Conclusion

The corrosion of steel bars caused by salt pollution, damage to structural members, and the harm to houses are major issues worthy of attention of engineers. It is especially important to strengthen construction quality management, strictly control material quality, and take corresponding measures for special environments.

From the perspective of the retrofitting and repair effects of the modified project, the retrofitting treatment technology is feasible and the effect is good. After the retrofitting treatment, it has passed the relevant quality inspection verification. It has been used for more than a year without any abnormalities. It can be seen that the excellent technical and economic performance of carbon fiber retrofitting concrete technology will inevitably make it occupy an important position in the field of building retrofitting, and has a good development space and prospects.