I. Overview of the Project
Taishan section of expressway, the western coast of Guangdong, is 86.28km long and is the expressway in the plain and hilly areas. There are 346 culverts, including slab culvert 170, round pipe culvert 167, arch culvert 8 and box culvert 1. It was completed and opened to traffic in April, 2002, with a fully enclosed interchange, designed as a two-way four-lane interchange. Because most of the Taishan section of expressway in the western coastal area is located in the soft foundation section, some culverts have different degrees of cracking, reinforcement exposure and other diseases under the dual effects of long-term vehicle load and subgrade settlement. In order to ensure the safety of expressway structure and the safe operation of road traffic, it is necessary to reinforce the diseased culvert. This paper briefly analyzes the causes and treatment measures of poor circular pipe culvert in Taishan section 15 of expressway in the western coastal area.
Second, the main diseases and causes analysis
1, culvert crack
There are one or more longitudinal cracks at the top of culvert pipe, which run through the whole pipe joint and belong to bending cracks, indicating that the bending resistance is not enough. This is mainly caused by the quality or stress of the culvert itself, and this kind of crack generally changes dynamically with the change of the load acting on the culvert; Some cracks are small and discontinuous, which are mainly caused by shrinkage and creep of concrete and belong to static cracks.
2, joint fall off, dislocation and sand infiltration
Joint void and dislocation are mainly caused by uneven settlement of foundation; Part of the joints are hollowed out and infiltrated with sand, which is caused by the aging and falling off of asphalt hemp strips, the water scouring the joints and the infiltration of subgrade fill.
4. The pipe wall is exposed
The exposure of steel bars on the pipe wall is mainly due to the thin thickness or excessive stress of the concrete protective layer, which leads to the cracking of the pipe wall and the corrosion of steel bars.
Third, the treatment measures
1, concrete crack
When the crack width is less than 0. 15mm, it should be sealed with modified epoxy resin adhesive. When the crack width is greater than or equal to 0. 15mm, the pressure grouting method is used to pour the modified epoxy resin adhesive for repair; Cracks that have been coated with epoxy resin but are not fully enclosed shall be chiseled out and repaired with modified epoxy resin. When the rebar in the crack area is corroded, the rebar shall be derusted first, and then the crack shall be repaired.
2. Structural crack reinforcement
For structural cracks with a width greater than 0.2 mm, in addition to repairing the cracks, the pipe culvert should also be strengthened to
Improve the bearing capacity of culverts. For structural stress cracks, bonded steel is used for reinforcement, and embedded steel lining is used for serious cracks.
3. The joint filler between pipe joints falls off.
When the joints or construction joints of concrete pipe culvert fall off, or have been repaired with cement mortar, but the repair quality is poor, the original joint sealant should be chiseled away, cleaned up and filled with dry linen soaked in asphalt. For subgrade seepage, quicksand and other phenomena, grouting should be carried out to reinforce the culvert back soil before plugging.
4. Cavities, honeycombs, pits, surface weathering, peeling and damage of the concrete on the pipe wall.
Remove the loose parts first, and then repair them with small stone concrete and modified epoxy mortar. The newly poured concrete should be dense, firmly combined with the original structure, and have a smooth surface. New concrete must be cured. When the concrete is exposed or the thickness of the concrete protective layer is insufficient, the loose protective layer should be chiseled away first, and the corrosion of steel bars should be removed, and then the protective layer should be repaired. If the damaged area is not large, it can be repaired with modified epoxy mortar; If the damaged area is too large and the steel bar is seriously corroded, it can be reinforced with steel casing.
5. staggered joint
Due to the uneven settlement of the foundation, the joint of the pipe joint is filled with asphalt hemp, and the local damage of the pipe joint is repaired with high strength concrete. If the pipe joint is seriously misaligned, it is recommended to correct it.
6. Other maintenance measures
For the cracks on the culvert top pavement, emulsified asphalt is used to seal the cracks, and cement mortar is used to repair the cracks on the end wall and wing wall.
Fourth, the construction technology and technical requirements
Crack repair
1. Before repairing cracks, conduct a comprehensive investigation, verify the number, length and width of cracks on site, number the cracks, make records and draw the crack distribution map.
2, according to the different properties, different shapes and occurrences of cracks, choose the appropriate repair method and repair sequence.
3, crack surface treatment, should make the working face level off, dry, no oil pollution, treatment range along the crack direction width is 30 ~ 50 mm. ..
4. When the surface sealing method is used to treat cracks, the joint surface should be treated and leveled with modified epoxy mortar under appropriate pressure.
5, pressure grouting to repair cracks According to the fluidity of the slurry, the grouting pressure is generally 0. 1~0.4MPa.
6, crack grouting must be carried out from bottom to top.
7. Construction process flow of pressure grouting method: surface treatment of grouting-pasting grouting nozzle and slurry outlet nozzle-sealing joint-sealing joint inspection-grouting-sealing end-inspection.
(2) Treatment of surface defects of pipe joints
1. Before repairing the surface defects of concrete, the defects should be investigated comprehensively, and appropriate repair materials and methods should be selected according to the damage degree.
2. For surface defects such as honeycomb, cavity and large area damage, concrete one grade higher than the original structure can be used to repair them; Modified epoxy mortar can be used to repair surface weathering, peeling, steel bar exposure and small area damage defects.
3, before concrete repair, deal with the surface of the honeycomb, holes, chisel hair, and keep the old concrete surface moist and clean.
4. Before applying modified epoxy mortar to repair, a layer of modified epoxy-based liquid should be coated on the rough concrete surface to fully penetrate the old concrete surface.
5. The construction temperature of modified epoxy mortar should be 20oC±5oC, and effective measures should be taken to control the construction temperature in high temperature or cold season.
6. Rusted steel bars should be derusted before surface defects are treated, and after defects are treated, a permeable antirust agent should be coated on the repair range and around.
(3) Reinforcement of steel-lined pipe culvert
The steel lining is made of 6mm thick steel plate, and the length of the lining is customized according to the cracking range and construction method of concrete, such as
When extension is needed, flat welding butt joint is adopted. The gap between the steel casing and the original concrete pipe culvert is filled with epoxy resin. In order to ensure that the liners can move smoothly in the hole, facilitate installation, and ensure that the liners are centered, a semicircular steel plate of 1 ~ 2 cm is welded under each barrel. Before installing the steel lining, the inner surface of the original culvert should be polished to remove impurities, stolen goods and cracked concrete, and then cleaned with a high-pressure water gun. The surface of steel casing should also be treated, mainly including the detection of salt content on the surface of steel plate and the removal of soluble salt, the inspection and removal of surface oil stains, and the removal of surface attachments and sundries such as paint and tape.
Installation of steel casing: excavator hoisting, winch traction. The upstream is provided with an excavator lifting steel casing.
A 5t hoist is installed downstream of the culvert, one end of the steel casing is pulled by a steel wire rope, and the bolt joint of the steel wire rope is welded with φ25mm steel bar to form a cross, so as to reinforce the nozzle and prevent the steel casing from being deformed. Material requirements: according to ISO 3549-2002 standard test, the weight ratio of metallic paint in epoxy zinc-rich primer in dry film is not less than 80%; The intermediate (MIO) of epoxy micaceous iron requires a volume solid content of not less than 80%; Acrylic polyurethane topcoat requires a volume solid content of not less than 57%.
Construction requirements: the sandblasting treatment on the surface of steel casing shall conform to the standard of Sa2.5. Shop primer shall be used for the surface of steel casing structure.
The construction temperature of primer and topcoat for inorganic zinc silicate workshop shall not be higher than 40℃. See Table 5 and Table 6 for the coating system on the inner surface of the steel casing and the coating system on the Site welding connection area. Before the surface of Site welding joint area is painted, it should be polished to St3 level with electric tools, and the construction should meet the requirements of relevant standards and specifications. Anticorrosive painting should be carried out when the atmospheric conditions are good, and painting cannot be carried out when the temperature is lower than the limit of drying and curing temperature of the paint or when it is foggy, frosted or rainy.
(4) Pipe joints are reinforced with steel plates.
1. Before the reinforcement construction, the concrete strength of the original pipe culvert must be tested on site, and the actual concrete strength grade should be no less than C20.
2. The steel plate shall be automatically made into circular arc by the factory, and the cutting edge surface shall be smooth without burr, undercut and warping.
3, steel plate joint surface shell with sand blasting or flat grinding wheel grinding to metallic luster, grinding lines should be perpendicular to the direction of steel plate stress, steel plate joint surface should have a certain roughness.
4. The exposed surface of steel plate must be derusted to show metallic luster, kept dry and coated with anticorrosive paint. Anticorrosive materials are harmless to steel plates and adhesives.
5, steel plate paste must be carried out in a dry environment, if the joint bonding surface is wet, it must be dry.
6. The treatment of the joint surface of pipe joint and the joint surface of steel plate is the most critical process. If the joint surface is damaged locally, it should be chiseled first, and then repaired with pebble concrete with higher strength grade of the original concrete. For the very old and dirty bonding surface, first brush off the oil stain and dirt on the surface with a hard brush dipped in an efficient cleaner, then rinse with water, then polish the bonding surface, remove the surface layer with a thickness of 2~3mm until the new concrete surface is completely exposed, and blow off the dust with compressed air.
7, paste steel plate construction, should be divided into frames and closed culverts, reduce the impact of live load on the quality of steel.
8. The steel plate surface coating system refers to the steel casing surface coating system.
Due to the small-scale and scattered maintenance and reinforcement project of circular pipe culvert, under the normal operating conditions in expressway, it is necessary to ensure the construction quality and safety and save the cost. Therefore, in addition to putting forward higher requirements in construction technology, we should also organize construction reasonably, including measures such as traffic maintenance and environmental protection.
The detailed information of "Culvert Disease Cause Analysis and Reinforcement Treatment" can be found in Zhong Da Consulting & Construction Link, and all relevant building construction information you want is available.
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