It is very important to analyze the causes of culvert diseases and strengthen them. It is critical to understand the causes of disease formation and the harm it will cause, and to deal with every detail. Zhongda Consulting will explain to you the cause analysis and reinforcement treatment of culvert diseases.
1. Project Overview
The Taishan section of the coastal highway in western Guangdong has a total length of 86.28km. It is a highway in a plain and hilly area. It has 346 culverts, including cover culverts. It has 170 seats, 167 round pipe culverts, 8 arch culverts and 1 box culvert. It was completed and opened to traffic in April 2002. It adopts a fully enclosed interchange throughout and is designed as a two-way four-lane. The design speed is 120km/h and the design load is Auto-Super 20, Vehicle-120. Since most of the Taishan section of the West Coast Expressway is located on a soft foundation section, some culverts have suffered varying degrees of damage such as cracking and exposed reinforcements due to the dual effects of long-term vehicle loads and roadbed settlement. In order to ensure the safety of highway structures and the safe operation of road traffic, it is necessary to reinforce damaged culverts. This article briefly analyzes the disease causes and treatment measures of 15 poor circular pipe culverts in the Taishan section of the Western Coast Expressway.
2. Analysis of main diseases and causes
1. Cracks in culverts
One or more longitudinal cracks appear at the top of the culvert, penetrating the entire pipe section, and are bending cracks , indicating insufficient bending resistance. This is mainly caused by the mass or stress of the culvert itself. This crack generally changes dynamically with the change of the load acting on the culvert. Some cracks are small and discontinuous, mainly caused by shrinkage and creep of concrete. It is a static crack.
2. Joint detachment, misalignment and sand seepage
Joint disengagement and misalignment are mainly caused by uneven settlement of the foundation; some joints are hollowed out and seeped. The sand is caused by the aging and falling off of the asphalt lint cloth strips, the erosion of the joints by water flow, and the seepage of the roadbed filling soil.
4. Exposed steel bars on the pipe wall
The exposed steel bars on the pipe wall are mainly caused by the thin thickness of the concrete protective layer or excessive stress that causes the pipe wall to crack and the steel bars rust and expand.
3. Treatment measures
1. Concrete cracks
When the crack width is less than 0.15mm, apply modified epoxy resin glue for sealing; When the crack width is greater than or equal to 0.15mm, the pressure grouting method is used to inject modified epoxy resin glue for repair; for cracks that have been painted with epoxy resin but are not completely closed, they are dug out and re-patched with modified epoxy resin. . When the steel bars in the cracked area are rusted, the steel bars are first derusted and then the cracks are repaired.
2. Reinforcement of structural cracks
For structural cracks with a width greater than 0.2mm, in addition to repairing the cracks, the pipe culvert should also be reinforced to
< p>Improve the carrying capacity of the culvert. For structural stress cracks, bonded steel plates are used for reinforcement, and for severe cracks, embedded steel casings are used for reinforcement.3. The filler of the joints between pipe joints falls off
The filler of the joints or construction joints of the concrete pipe culvert falls off, or the cement mortar has been used to repair it, but the repair quality is not good. The best method is to remove the original caulking material, clean it, and use dry hemp wadding soaked in asphalt to fill it tightly. For phenomena such as water seepage and quicksand in the subgrade, the soil on the back of the culvert should be reinforced with grouting first, and then sealed.
4. Cavities, honeycombs, pitted surfaces, surface weathering, peeling, and damage in the pipe wall concrete
First remove the loose parts, and then use small gravel concrete and modified epoxy mortar Make repairs. The newly added concrete should be dense, firmly integrated with the original structure, and have a smooth surface. New concrete must be cured. When concrete peels off and exposes reinforcements or the thickness of the concrete protective layer is insufficient, first chisel off the loose protective layer, remove the rust on the steel bars, and then repair the protective layer. If the damaged area is not large, modified epoxy mortar can be used to repair it. If the damaged area is too large and the steel bars are seriously corroded, steel sleeves can be used for reinforcement.
5. Misalignment of pipe joints
For pipe joints that are misaligned due to uneven settlement of the foundation, the joints should be filled with asphalt fluff, and the local damaged pipe joints should be filled with High-strength grade concrete is used for repair. If the pipe joints are seriously misaligned, it is recommended to correct the deviation.
6. Other maintenance measures
For road cracks on the culvert top, use emulsified asphalt grouting to seal them, and for end wall and wing wall cracks, use cement mortar to repair them.
IV. Construction technology and technical requirements
(1) Crack repair
1. Before crack repair, a comprehensive investigation of the cracks should be carried out and the number of cracks should be verified on site. , length, width, etc., number the cracks, keep records, and draw a crack distribution map.
2. Select the appropriate repair method and repair sequence according to the different properties and shapes of cracks.
3. The surface treatment of cracks and seams should make the working surface smooth, dry and free of oil stains. The treatment range should be 30~50mm wide along the direction of the cracks.
4. When using the surface sealing method to treat cracks, the surface of the crack should be treated and scraped with appropriate pressure using modified epoxy glue.
5. Pressure grouting to repair cracks selects the grouting pressure according to the fluidity of the slurry, which is generally 0.1~0.4MPa.
6. Fracture grouting should be carried out from bottom to top.
7. Pressure grouting method construction process: seam surface treatment - pasting grouting nozzle and grout outlet - seam sealing - sealing inspection - grouting - end of sealing - inspection.
(2) Treatment of pipe joint surface defects
1. Before repairing concrete surface defects, a comprehensive investigation of the defects should be conducted, and appropriate repair materials and repair methods should be selected according to the degree of damage.
2. For surface defects such as honeycombs, cavities and large-scale damage, concrete of a grade higher than the original structure can be used to repair; for surface weathering, peeling, exposed tendons and small-area damage defects, it can be repaired. Use modified epoxy mortar for repair.
3. Before concrete repair, the honeycombs and cavities on the surface should be processed and roughened, and the old concrete surface should be kept moist and clean.
4. Before applying modified epoxy mortar for repair, a layer of modified epoxy base liquid should be applied to the roughened concrete surface to fully infiltrate the old concrete surface.
5. The construction temperature of modified epoxy mortar should be 20oC±5oC. Effective measures should be taken to control the construction temperature in high temperature or cold seasons.
6. Rusty steel bars should be derusted before surface defects are treated. After defects are treated, penetrating rust inhibitors should be applied to the repair area and surrounding areas.
(3) Pipe culvert lined steel casing reinforcement
The lining steel casing is rolled from 6mm thick steel plate, and the casing is customized according to the cracking range of the concrete and the construction method. Length, if
needs to be extended, use flat butt welding connection. The gap between the steel casing and the original concrete pipe culvert is filled with epoxy resin. In order to ensure that the casing can move smoothly in the hole, facilitate installation, and ensure that the casing is centered, a 1 to 2 cm semicircular steel plate is welded under each section of the cylinder. Before installing the lined steel casing, sandblast the inner surface of the original culvert to remove debris, stolen goods, and cracked concrete, and clean it with a high-pressure water gun. The surface of the steel casing should also be treated, which mainly includes the detection of salt content on the surface of the steel plate and the removal of soluble salts, the inspection and removal of surface oil stains, and the removal of surface attachments and debris such as paint and tape.
Steel casing installation: hoisting by excavator and pulling by winch. Set up an excavator upstream to lift the steel casing
A 5t winch is installed downstream of the culvert, and a steel wire rope is used to pull one end of the steel casing. The wire rope is welded into a cross shape with φ25mm steel bars, and the pipe mouth is Reinforcement to prevent deformation of steel casing. Material requirements: According to the ISO3549-2002 standard test, the weight ratio of the metallic paint in the epoxy zinc-rich primer in the dry film is not less than 80%; the volume solid content of the epoxy mica iron intermediate paint (MIO) is required to be not less than 80 %; the volume solid content of acrylic polyurethane topcoat is required to be no less than 57%.
Construction requirements: The sandblasting treatment on the surface of the steel casing should meet the Sa2.5 standard. The shop primer is used on the surface of the steel casing structure.
Inorganic zinc silicate shop primer is used, and the application temperature of the topcoat should not be higher than 40°C. The coating system for the inner surface of the steel casing and the coating system for the welded joint area at the construction site are shown in Table 5 and Table 6 respectively. Before painting the surface of the welded joint area on the construction site, power tools should be used to polish it to St3 level. The construction must meet the requirements of relevant standards and specifications. Anti-corrosion coating should be carried out when the atmospheric conditions are good. Painting cannot be carried out when the air temperature is lower than the drying and curing temperature limit of the paint or when there is fog, frost or rain.
(4) Steel plate reinforcement for pipe joints
1. The strength of the original pipe culvert concrete must be tested on-site before reinforcement construction, and the actual concrete strength grade is required to be no less than C20.
2. The steel plate should be automatically made into an arc shape by the factory, and the cutting edge surface should be smooth without defects such as burrs, bites, and warping.
3. Use sandblasting or a flat grinding wheel to polish the bonded surface of the steel plate until the metallic luster is exposed. The grinding texture should be perpendicular to the force direction of the steel plate, and the bonding surface of the steel plate should have a certain roughness.
4. The exposed surface of the steel plate must be rust-free until it shows metallic luster and kept dry, and painted with anti-rust paint. The anti-rust material is harmless to the steel plate and adhesives.
5. The steel plate pasting should be carried out in a dry environment. If the bonding surface of the pipe section is relatively moist, it must be dried.
6. The bonding surface treatment of the pipe joints and the bonding surface treatment of the steel plate are the most critical processes. If the bonding surface is partially damaged, it should be roughened first, and then use a small concrete with a higher strength grade than the original concrete. The gravel concrete should be repaired before processing. For very old and dirty bonding surfaces, first use a hard-bristled brush dipped in high-efficiency detergent to brush off the surface oil and dirt, then rinse with clean water, and then polish the bonding surface to remove the 2~3mm thick surface layer until the new concrete is completely exposed. surface and blow away dust with compressed air.
7. When gluing steel plates, the construction should be carried out in sections and the traffic on the culvert should be closed to reduce the impact of live load on the reinforcement quality.
8. The steel plate surface coating system refers to the steel casing surface coating system.
Since the round pipe culvert repair and reinforcement projects are small and relatively scattered, it is necessary to ensure the construction quality and safety while saving costs while ensuring the normal operating conditions of the expressway. Therefore, in addition to putting forward higher requirements in terms of construction technology and other aspects, construction must be reasonably organized, including traffic maintenance, environmental protection and other measures.
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