Project Overview

In a power plant substation, there are more than 50 concrete circular poles in the station, which are connected with beams and walkway slabs to form a frame. The walkway can be used for pedestrians and supporting equipment. The station has been in use for more than 30 years. In addition, the strength level of concrete used in the production of concrete poles in my country in the past is generally low. After years of outdoor use in the sun and rain environment, the poles have different degrees of erosion, rust and aging, and there are many vertical cracks on the outside of the surface of some columns. The minimum width of the crack is about 0.5mm, and the maximum width is about 0.8mm, which has exceeded the 0.3mm allowed by the specification. In order to ensure the safe use of the pole structure, the defects of the pole must be dealt with.

Component structural strengthening reinforcement analysis and plan selection

Analysis of the original prisoners of component damage: The pole structure is intact, and the superstructure cracking problem caused by the foundation has been eliminated. The main cause of the cracking is the aging of the stone, the steel bars in the stone are corroded, and the steel bars are oxidized to form iron trioxide and expand, which makes the stone swell and explode, and then a vicious circle, intensifying the development of cracks.

Selection of reinforcement schemes: The commonly used methods for reinforcement of reinforced concrete structures in engineering mainly include the method of increasing section (that is, pouring reinforced concrete with a certain thickness on the original structure), external prestressed reinforcement method (that is, adding fulcrums and brackets to change the force system), seismic isolation and energy dissipation reinforcement method, and carbon fiber reinforced polymer strengthening method (including outsourcing and pasting reinforcement), etc.

As concrete aging is the cause of component damage, it is determined that the purpose of reinforcement is to restore the bearing capacity of the pole, and at the same time to paint a protective film on the surface of the concrete to prevent the continued aging of the concrete. Through the analysis of the above several reinforcement schemes, combined with the site restrictions and the characteristics of the sting, the carbon fiber reinforced polymer strengthening method was finally selected.

Compared with other reinforcement methods, the use of arbon fiber reinforced polymer strengthening has the advantages of high tensile strength (10 times that of ordinary steel), light weight, strong corrosion resistance and durability, simple construction, and short construction period. After the reinforcement is completed, the thickness is only about 2mm, which basically does not increase the cross-section of the component, and can ensure that the carbon fiber wrap works with the original component.

Reinforcement construction plan and technical measures

1 surface treatment

Use tools such as grinding stones, wire brushes, etc. to polish the concrete surfaces of the support rods and beams. Be careful to spray water slightly while polishing to prevent dust from splashing. The surface is required to be smooth, and oil and dust should be cleaned. Remove the cracked part of the concrete and expose the corroded steel bars. Clean it with a wire brush and wipe it with acetone. After chiseling the surface, fill in the polymer cement mortar to remake the protective layer. The construction and maintenance period should be waterproof and rainproof.

2 Construction technology of pasting carbon fiber wrap

(1) Substrate pretreatment:

• Remove the loose concrete surface to expose a solid base layer, and clean it up. Use tools such as grinding stones and wire brushes to remove impurities such as scum, oil and other impurities on the surface of the concrete. The concrete on the base surface of the component should be smoothed, especially the convex parts of the surface.

• Use a water spray bottle to spray water to clean the surface of the concrete and keep it dry

(2) Apply primer:

• Put the glue in a thousand containers, mix evenly, determine the dosage according to the actual weather and temperature on site and strictly control the use time.

• Spread evenly on the surface of the concrete with a brush, wait for the glue to solidify (the solidification time depends on the on-site temperature, subject to dryness to the touch), and then proceed to the next step of construction.

• Open flames are strictly forbidden at the construction site, pay attention to ventilation.

(3) Paste carbon fiber wrap:

• Cut the carbon fiber wrap according to the size required by the design, and the lap length of the carbon fiber wrap is 200mm.

• Mix and mix the paste materials, and then evenly apply to the area to be pasted, and apply more to the concrete joints, corners and other parts.

• Paste the carbon fiber wrap, and use a special roller or scraper to repeatedly roll along the fiber direction to remove air bubbles and make the carbon fiber wrap soak with the sizing glue.

• Spread the soaking glue evenly on the surface of the last layer of carbon fiber wrap.

Conclusion

During the construction of this project, under the premise of ensuring safety, only simple scaffolding was used for construction, which was convenient for construction, short construction period and reasonable cost. Carbon fiber materials are more and more widely used in structural reinforcement projects. Among existing reinforcement methods, carbon fiber materials are generally recognized for their excellent mechanical properties, simple construction technology and good effects.

The technology has achieved the expected results in terms of construction period, material durability, construction quality, etc. Its comprehensive economic and social benefits are good, and it has broad application prospects and is worthy of vigorous promotion.