Bridge Rehabilitation And Strengthening

1. Project overview

The Yunquan Super Bridge is a box-shaped arch bridge with a main span of 160m. The design load of the bridge is automobile-super 2O, and the trailer is 12O. The structure of the bridge deck on the arch is a 13×13m reinforced concrete hollow slab, and the main arch ring is made of C40 concrete. The reinforced concrete bridge deck on the arch is made of C25 concrete. The 13m slab on the arch is not continuous, and the expansion joints between the slabs and the slabs are filled with asphalt flax.

In May 2014, when CCCC First Highway Survey and Design Institute Co., Ltd. inspected the bridge, it was found that the upper structure and lower structure of the bridge had cracks, exposed tendons, water seepage, concrete honeycomb pockmarked surface, damage, spalling and other conventional diseases . Since the concrete strength of the deck slab within the main arch circle of the whole bridge is C25, according to the "Code for Design of Highway Bridge Reinforcement", it is not appropriate to use prestressed carbon fiber plate for reinforcement, but to use the solution of pasting carbon fiber plate. .

2. Brief analysis of disease

Cracks are one of the most common diseases in reinforced concrete bridges, and there are few bridges without cracks. The hollow slab of the reinforced concrete bridge over the arch appears transversely distributed cracks, the length of which is mostly 0.5m～8m, the width is between 0.02mm～0.2Omm, and the cracks mainly appear in the range of 1/4L～3/4L. There are 1-3 longitudinal cracks in the bottom plate with a span of more than 2/3, the length is between 1m and 5m, and the width is between 0.05mm and 0.22mm, which are mainly located at the center line of the half bridge. There are five vertical cracks in the web, the length of the cracks is between 0.1m and 0.4m, and the width is between 0.02mm and 0.18mm, mainly in the range of 1/4L to 3/4L. There are multiple water seepage calcifications in the bottom plate of more than 2/3 spans, and calcification crystals are precipitated. The water seepage and calcification area is about 0.5m×0.5m, accompanied by the phenomenon of steel corroded concrete falling off.

3. Carbon fiber plate reinforcement construction technology of Yunquan Bridge

3.1 Preliminary work of carbon fiber plate reinforcement

(1) Hollow slab drilling and drainage seems simple, but it requires meticulousness. First find the location of the borehole, generally 0.2-0.3m away from the end of the slab on the side of the low longitudinal slope or where there is obvious water seepage and calcification. To avoid the location of steel bars and steel strands, use an electric hammer to drill holes with a diameter of 12mm. Finally, drill holes 0.2-0.3m away from the end of the slab on the side of the high longitudinal slope, and then use an air compressor to go deep into the slab for auxiliary drainage. After the stagnant water is drained, install a PVC sleeve at the position of the drain hole. The PVC sleeve should extend at least 5cm from the hole.

(2) Crack treatment includes crack sealing and crack grouting. For cracks with a width less than 0.15mm, use epoxy resin for sealing treatment.

1) To treat the surface of the 砫, first use a wire brush or other tools to remove the loose objects such as dust, white ash, scum, etc. on the 砫 surface along the cracks.

2) Apply a layer of epoxy resin base liquid on both sides of the crack and then apply a layer of epoxy resin cement to prevent small pores and air bubbles.

3) Brush two layers of epoxy resin base liquid on the surface. The cracks with a width of 0.15mm are grouted with epoxy resin.

(3) Concrete defect repair mainly includes rust removal and mortar leveling. Rust removal is to clean the oxide layer of steel bars. Use epoxy grout to paint on the surface of exposed steel bars or rusted concrete surfaces, and evenly apply to the concrete roots. Mortar leveling is to make the concrete surface clean, moist and water-free, then apply the mixed epoxy mortar to the concave and peeling parts of the concrete with a mortar knife to make it bond with the concrete densely without bubbles. The repair is carried out in layers to ensure a smooth transition between the repaired area and the unrepaired area.

3.2 Process of pasting and strengthening carbon fiber plate

The main steps of the carbon fiber plate pasting process include:

Surface cleaning, after the concrete defect is repaired, use a blower or brush to remove the surface dust until the surface is clean;

Apply primer. Determine the ratio of the main agent of the primer and the curing agent, stir and mix well, and evenly apply the primer to the bonding surface with a roller or brush. The adjusted primer should be used up within the specified time. Generally, the construction temperature is above 5℃ and the humidity is below 85%. It is suitable for the next construction when the fingers are dry. The concave part of the base surface must be repaired and flattened with repairing glue to ensure that there are no edges or corners. The corners should be repaired to a smooth arc with a radius> 2cm. The convex surface should be smoothed with sandpaper. The primer should be able to withstand the disturbance of passing vehicles.

Paint epoxy resin. After the leveling material is dry to the touch. Use rolling brush or brush. The squeegee is coated with epoxy resin on the primer, and the thickness of the coating should be uniform and not sag:

Paste the carbon fiber plate and paste the fiber plate evenly on the bonding surface. Use a special roller to roll in the direction of the fiber many times to drive out the bubbles and promote the penetration of the adhesive.

4 Conclusion

The reinforcement of Yunquan Bridge was completed at the end of September 2015. The flexural load-bearing capacity and crack resistance of the front section of the main beam are significantly improved. Passed the bridge inspection and achieved the purpose of strengthening the bridge. Through the application of carbon fiber plate in the reinforcement project of Yunquan Bridge, compared with the traditional enlargement of concrete cross-section or bonding steel reinforcement technology, its construction operation is simple and the construction quality is easy to ensure that the dead load and appearance of the bridge are basically not affected. Corrosion resistance and durability are good, the service life of the structure is increased, and the reinforcement cost is reduced, so it has popular value in the bridge reinforcement project.