Bridge reinfrocement

General situation of rear bridge ditch bridge

The rear bridge bridge is a small bridge on the 308 line of national highway under the jurisdiction of our bureau. It was built in 1989. The upper structure is simply supported hollow slab, and the lower part is the pier cap beam pier. The combination of bridge span is 3 X10 meters, and the combination of bridge width is 0.5 + 17 + 0.5. As G308 is an important trunk line of "West-East Coal Transportation Project", it has a large load and traffic volume. In order to solve the increasingly serious traffic problems, the line was rebuilt in 2002. The road surface was widened from 10 m to 15 m, and the bridge deck from 11 m to 17 M. Limited to capital, the old bridge deck is still used in the old part of the bridge. As time goes on, the disease of the bridge is increasingly revealed. In 2007, the provincial Bridge Inspection Center identified it as the three kind of bridge. The main defects of the old bridge deck slab are that most of the transverse cracks and longitudinal cracks appear at the bottom of the old bridge deck slab.

Causes of disease

1. the main reason for cracks is due to the thin protective layer of concrete at the bottom of the slab, the corrosion of reinforcing steel and the expansion of concrete.

2. Long bridge age, cumulative damage cracks appear in bridge slab concrete, concrete cracking, steel corrosion, steel corrosion and aggravated concrete cracking.

Treatment countermeasures

In view of the problems of the bridge, in July 2008 Liaocheng Highway Bureau Maintenance Department, Survey Institute, Provincial Bridge Inspection Center and other relevant experts to the bridge consultation. Decided to paste carbon fiber fabric to reinforce the bridge to meet the bearing capacity and ensure driving safety.

Characteristics of carbon fiber fabric reinforcement

Carbon fiber is a new type of building materials, with light weight, high strength, corrosion resistance, easy construction, can adapt to a variety of complex shape structure characteristics, and does not affect the size and appearance of the structure, and the reinforced carbon fiber cloth hardly needs any maintenance work, can reduce the cost of late maintenance.

According to the different degree of disease of each block, the following construction plans are worked out.

Determine the scope of treatment

1. Bridge deck with three carbon fiber fabrics.

The first hole second, fourth, fifth, 7, 8 plates.

Second holes third, fourth, seventh, 11 plates

The third, sixth, ninth holes in the third hole.

2. Bridge deck with two carbon fiber fabric

First hole eleventh, twelfth boards

Second holes and first, twelfth boards

The twelfth holes in the third hole.

3. Construction steps of sticking carbon fiber fabric

3.1 construction technology

Preparations for construction, surface treatment of structural concrete, preparation of brush primer, surface repair with leveling materials, preparation of brush impregnated resin, paste carbon fiber cloth, brush impregnated resin, surface protection treatment

3.2 concrete surface defect treatment

3.2.1 Clean the surface of concrete such as honeycomb, linen surface, corrosion, peeling, weathering, floating slurry, dirt and so on to the compact surface by grinding machine or wheel.

3.2.2 check the exposed steel bar, rust and rust, and then brush the red Dan paint.

3.2.3 repairs cracks. Epoxy injection resin is used to seal the cracks whose width is less than 0.2 mm, and epoxy resin is used to seal the cracks whose width is greater than 0.2 mm.

3.2.4 positioning and marking of carbon fiber fabric should be carried out according to design requirements.

3.2.5 The protruding part of the surface of the component caused by construction shall be ground with a polishing machine or a grinding wheel, and the height difference shall not exceed 1 mm.

3.2.6 A pair of edges and corners on the surface of the components shall be rounded by a polishing machine. The radius of the rounded corners shall be greater than 30 mm and not less than 20 mm.

3.2.7 A pair of concrete surface defective parts, after removing loose concrete with the strength of the original component concrete mortar repair to the surface of the flat.

3.2.8 uses high pressure water or compressed air to remove the dust on the surface of the component and make it fully dry.

3.3 coating base glue

3.3.1 after accurately weighing the main agent and curing agent prepared according to the chemical examples, put them into the container and mix them evenly. The first mixing amount shall be used up within the available time. If the amount exceeds the available time, it shall not be used.

3.3.2 apply the primer evenly with the roller brush. If two layers are needed, apply the second layer after the first finger touch is dried.

3.3.3 refers to the variation of drying time between 3 hours and 1 day due to different temperatures.

3.3.4 after the sole is hardened, when there is a bulge on the surface of the component, it shall be smoothed with a grinder or sandpaper.

3.3.5 select appropriate bottom glue according to the temperature and humidity of the construction site. Under the temperature 5 ℃, relative humidity is more than 85%, concrete surface moisture content over 8%, rainy days or condensation may be without effective safeguard measures, construction is not allowed.

3.4 scratch leveling glue

3.4.1 CFRP can produce good reinforcement effect only when it is in close contact with the reinforced concrete surface. The surface of components such as honeycomb, hemp surface, small hole and so on are the reasons for bulging caused by improper adhesion of carbon fiber cloth materials. Flattening glue is used to fill in and repair the surface to be smooth.

3.4.2 leveling glue after scratching, the surface of the rough lines, the use of sandpaper grinding leveling.

3.5 Paste the carbon fiber fabric

3.5.1 in order to prevent damage to the carbon fiber, it shall not be overly bent during the transportation, storage, cutting and pasting of the cloth. Therefore, the clip cutter is used to cut off the carbon fiber fabric according to the specified size before pasting the carbon fiber fabric, and the length of each segment should be no more than 6m.

3.5.2 before cutting, a wide adhesive tape should be pasted at the cutting position and cut at the middle position of the wide adhesive tape to ensure a clean cut of the carbon fiber fabric.

3.5.3 before pasting the fabric, make sure that the repairing materials such as resin glue and leveling glue on the construction surface have reached finger contact drying.

3.5.4 the main agent and curing agent of impregnated resin shall be weighed accurately according to the specified proportion, loaded into the container and stirred evenly. One mixing quantity should be used up within the available time, and should not be used beyond the available time.

3.5.5 before paste, use the roller to evenly smear the impregnated resin on the paste surface, which is called undercoat. Standard of lower coating: 200g/m carbon fiber fabric, 400g-500g/m; 300g/m carbon fiber fabric, 600-700g/m.

Quantity is according to construction place and rough degree and change, corner part, fiber cloth lap part and incomplete repair place should use a few more.

3.5.6 the longitudinal joint of fiber cloth must be tower over 10cm, and the part should be coated with impregnated resin, and no lap is required.

3.5.7 when pasting, it shall be pasted from top to bottom and from left to right in an orderly manner, and no space shall be left in the carbon fiber fabric. For this purpose, the cylinder can be rolled on the carbon fiber fabric several times along the fiber direction to make the impregnated resin fully infiltrate into the fiber, and the air bubbles can be removed with the pressure plate. Observe whether the patch is bonded and compacted immediately. If any gap or bubble is found, it should be treated in time.

3.5.8 after the carbon fiber fabric is pasted for 30-60 minutes (according to the degree of drying), the carbon fiber fabric is then evenly coated with the impregnated resin by the roller. The roller will roll along the direction of the fiber when the coating is applied. Coating standard: 200g/m carbon fiber fabric, 200-100g/m; carbon fiber fabric of 300g/m, 300-200g/m. As with the top coat, use the pressure plate to scrape along the fiber direction for 2-3 times to fill the fiber with the impregnated resin.

3.5.9 empty drum inspection shall be carried out within 3-4 hours after being applied, and the blank drum rate, drawing strength and adhesive thickness of fiber cloth shall be checked according to technical specifications for strengthening and repairing concrete structures with unidirectional carbon fiber sheet.

3.6 maintenance

3.6.1 After pasting carbon fiber fabric, it should be naturally maintained for 24 hours to reach initial curing, and ensure that the curing period is not disturbed.

3.6.2 Carbon fiber fabric after pasting to achieve the design strength of the natural maintenance time required: when the average temperature above 20 degrees Celsius takes a week.

3.7 coating

3.7.1 Coating shall be carried out after the initial curing of the resin and shall comply with the relevant standards and construction requirements of the coatings used.

3.7.2 coating materials should be selected according to the needs of weathering materials and refractory materials. It is consistent with the appearance and color of reinforcement components.

3.8 requirements for raw materials and construction machinery

3.8.1 All construction materials, including carbon fiber cloth and cementing materials must meet the design requirements, which is the premise to ensure the quality of the project.

3.8.2 The rolled materials shall not be laid flat or extruded during transportation and storage so as to avoid damage to carbon fiber cloth, nor shall they be exposed to sunlight or rain, and the cementing materials shall be unopened in their original form.

3.8.3 Containers, mixing equipment, brushes, drums and other tools must be cleaned in a timely manner, no residue of cement.

Construction effect analysis

The use of carbon fiber fabric to strengthen the girder bridge is convenient for construction and shortening the construction period and saving investment. After the completion of the project, the observation and measurement of the deflection change of the bridge slab when the heavy truck passes shows that the disturbance of the slab is greatly reduced. The maximum deflection of the measured slab before reinforcement is 1.1 cm, and the maximum deflection after reinforcement is 0.7 cm, which greatly improves the bearing capacity of the slab and ensures the driving safety. The durability of the bridge strengthened with CFRP fabric depends on the aging failure time of epoxy resin adhesive. We will track and observe the service condition of the bridge strengthened with CFRP fabric, and accumulate experience for strengthening concrete members with CFRP fabric.