As an important part of highway structure, bridge plays an important role, and bridge expansion joints, as auxiliary facilities in bridge structure, are often ignored by builders and managers, and the phenomenon of expansion joint damage in bridge operation is more common.

This paper discusses the design and construction of expansion joints, and analyzes the maintenance and health care after damage, which provides reference for highway maintenance.

Keywords: bridge expansion joint maintenance

1 overview

As an important part of highway structure, bridge plays an important role, and bridge expansion joints, as auxiliary facilities in bridge structure, are often ignored by builders and managers, and the phenomenon of expansion joint damage in bridge operation is more common.

If the expansion joint is not repaired in time after being damaged, it will affect the driving safety of the pavement and there are certain safety hazards.

The later maintenance of expansion joints is carried out under the condition of opening to traffic, which has high maintenance cost, great difficulty and poor maintenance effect.

In order to ensure the good quality of expansion joints, the initial construction should be carried out in strict accordance with the technology, and the later construction should be kept in place, so as to ensure the quality of expansion joints and the safe and smooth road traffic after opening to traffic.

2 factors affecting the quality of expansion joints

There are many factors affecting the quality of expansion joints, mainly including design, construction and maintenance.

2. 1 design factors

The design of bridge expansion joints should be determined according to the length, span and structural form of the bridge.

Expansion is an important index of expansion joint design, and there are many factors affecting expansion, including temperature, concrete shrinkage and creep, various loads, pier displacement and so on. The above factors should be fully considered in the design to determine the expansion, so as to avoid the occurrence of insufficient expansion.

2.2 Construction factors

Construction should be carried out in accordance with strict technological requirements, and problems in any link may lead to damage of expansion joints during use.

The first is the material requirements. The compressive strength of concrete is not less than 50Mpa, and the flexural tensile strength is not less than 6.8Mpa. Grade II steel fiber, model sp-25, and R235 and HRB335 are used for ordinary reinforcement. The expansion device is selected according to the design requirements, and the matching rubber has good sealing performance.

Construction shall be carried out according to the following technological requirements: reserved notches are in place-the deviation of embedded steel bars shall not exceed 20mm, and the length of embedded concrete shall not be less than 35d(d is the diameter of steel bars)-joint cutting, groove cleaning and reinforcement (no missing or broken steel bars, etc. )-leveling and welding of lower joint-formwork hanging, steel bar covering-installation of water stop-concrete pouring.

2.3 Health factors

The maintenance of cement concrete is also a key step, but it is often ignored by builders.

Health care should be carried out according to the following steps: cover with straw bag or plastic film, water frequently and keep moist.

Before the strength of cement concrete reaches 90%, no vehicles are allowed to pass to prevent the expansion device from loosening or the cement concrete from being damaged. Traffic can not be opened until the concrete age reaches the time limit.

3 Repair and maintenance of expansion joints

3. 1 expansion joint maintenance is generally carried out in open sections, and the safety and smoothness of the construction site is extremely important, especially in sections with heavy traffic. It is necessary to formulate a detailed construction smoothness plan, which can only be implemented after being approved by the traffic police and the road administration department.

Site warning signs and warning cones must be placed in accordance with the requirements of Safety Operation Rules for Highway Maintenance.

3.2 When cleaning the damaged part of concrete, it must be removed to the top of beam slab. The joint between the damaged part and the intact part needs to be cut neatly, so that the maintenance part can be better integrated with the original part. All the laitance on the concrete surface must be knocked off, and the middle seam should be cleaned with a blower.

3.3 Pay attention to cold bending when re-binding and welding damaged steel bars. Hot bending is not allowed. The diameter of the reinforcement hole should be greater than the diameter of the reinforcement. In the process of steel bar connection, closed steel bars must be adopted, and the direction of steel bars is symmetrical. Cracked or broken steel bars are not allowed.

3.4 The thickness of the formwork shall be 5cm thicker than the width of the notch, 20cm long and 4cm lower than the depth of the notch. Support should be firm, it is best to bind it with steel wire rope, and it is absolutely not allowed to leak slurry, so as to avoid blockage between beams and slabs.

3.5 Before concrete pouring, clean the groove with blower again, and rinse it with clear water, leaving no residue.

3.6 concrete pouring should be mixed at the scene according to the mixture ratio. According to the seasonal characteristics, some accelerator and steel fiber can be added appropriately to shorten the curing period.

When pouring, use an internal vibrator to vibrate evenly and close the surface for three times to ensure that the concrete surface is flat and smooth.

3.7 The last step is the curing of concrete. If curing is not done well, all previous achievements will be in vain.

It is best to use plastic film for health preservation. If there is no plastic film, geotextile can be used instead.

When keeping in good health, it must be sealed tightly, and air is forbidden to enter. Health geotextile must be watered more than three times a day and heated in winter.

During the maintenance of open road sections, it is necessary to strengthen inspections to ensure that no vehicles pass.

The curing time must be more than 7 days, and it can only be opened to traffic after the strength is measured with a rebound instrument.

4 conclusion

According to different site environments, the maintenance and construction of expansion joints are different. In order to avoid the secondary maintenance of expansion joints after opening to traffic, the construction technology should be strictly followed in the construction stage to ensure the construction quality of expansion joints.

References:

Zhang Weiguo. Key Technology of Bridge Expansion Joint Construction [J]. Engineering Construction and Design, 2007(04).

[2] Rui-qi Li. Study on reinforcement method of bridge expansion joint [J]. hunan communication science and technology, 2003(02).

Uncle Huang. Construction and control of bridge expansion joints [J]. Liaoning Communications Technology, 2005(02).