1, Introduction
As one of the important types of advanced bridge deck pavement, cement concrete pavement has been widely used. Cement concrete pavement has the advantages of high strength, good durability and low maintenance cost. However, there are still many problems in the use of bridge pavement in China. For example, the imperfection of the original design theory, the lack of construction experience and the neglect of maintenance have led to structural damage or functional defects in many bridge pavements, resulting in early diseases and other problems, which have seriously affected the quality of highway use.
Developed countries such as the United States have always had a special liking for using asphalt overlay technology to strengthen old cement concrete pavement, because asphalt overlay has two functions: improving the bearing capacity of pavement structure and restoring the surface function of old cement concrete pavement. Through a lot of research on test roads, countries have put forward corresponding asphalt overlay design methods, such as AI, AASHTO, ARE, Ta, etc. [2], constantly improve and develop the design method of asphalt overlay on old bridge pavement. However, these empirical methods abroad are quite different from the traditional theoretical methods in China, so they cannot be copied and applied, and can only be used for reference on the basis of theoretical analysis.
Paving asphalt layer on the original concrete slab is one of the effective measures to restore pavement function and strengthen and transform. After the asphalt layer (AC) is strengthened, it not only improves the bearing capacity of the pavement and prolongs its service life, but also eliminates the adverse effects of the original joints, improves the use function and improves the service level of the pavement [5]. At the same time, paving asphalt layer has the advantages of fast construction speed and little impact on traffic.
2, bridge pavement measurement
The scientific investigation and analysis of bridge pavement is of great significance to the formulation and implementation of old bridge pavement repair scheme. After obtaining the survey data, qualitative analysis and quantitative calculation can be carried out.
2. 1 investigation content
In order to obtain more detailed analysis data, the design, construction, maintenance and use of existing bridge pavement are comprehensively investigated from the following aspects: pavement structure; Pavement damage; Drainage conditions; Construction data; Maintain information; Traffic conditions.
2.2 survey methods
The design index, construction technology and construction control technology of cement concrete bridge deck pavement built in different periods are different. The principles to be considered in road section division are [2]: a. Design conditions; The design traffic volume is consistent with the design service life; The design thickness and structural type of pavement surface and base are consistent; Treatment method of longitudinal slope of pavement: subgrade filling and excavation type, dry and wet type are consistent with soil and hydrogeological conditions. B. The construction conditions, construction time and completion time are close; The same is true for the construction unit. C. Service status: maintained by the same (county-level) maintenance company; The existing traffic volume and axle load are basically the same; The types and quantities of main pavement diseases are close.
Work can be carried out in the following aspects: structural investigation; Damage investigation; Investigation of drainage conditions; Construction data survey; Maintain data survey; Traffic survey.
3, bridge pavement maintenance technology
3. 1 crack treatment technology
Sealing materials include epoxy resin, polyurethane and modified polyurethane, olefin and asphalt rubber. Epoxy resin caulking material has the advantages of heat resistance, high activity, high cohesion, strong adhesion and low shrinkage, but low elongation and brittleness, so it is necessary to modify epoxy resin and add low molecular weight liquid modifier, toughening agent and toughening agent. Commonly used modified epoxy resin materials include polysulfide modified epoxy caulking materials and two-component rapid curing caulking materials.
3.2 Staggered Platform Processing Technology
For the plates with staggered platforms, firstly, the smoothness is restored by grouting adjustment. After adjustment, there is still a height difference, and the dislocation amount is less than10 mm. The higher part can be smoothed by a building smoothing machine or manually chiseled, and the chisel (grinding) width is generally 10 ~ 30cm. When the dislocation amount is greater than 10mm, the low side is lined with asphalt sand or fine-grained asphalt macadam, and the lining length is1~ 2% of the height difference; Thin polymer cement mortar can also be used for repair. Before repair, the original pavement should be cleaned with a wire brush [1].
3.3 Non-structural STD hazard treatment technology
For structural diseases with large pits, exposed bones and poor flatness, asphalt concrete overlay [4] is often used, and the thickness should be greater than 2.5cm. The construction should meet the requirements of Technical Specification for Asphalt Pavement Construction, and the broken slab and the whole pavement should be repaired and grouted before overlay. Generally, the pockmarked surface can be treated without treatment, and only the severely exposed part can be treated with full-face treatment. Polymer mortar can be made into a thin layer, and the mixing ratio is cement: sand = 1: 2, and it is stirred with J6 glue solution to a uniform consistency. Apply IV ultra-early strength interfacial agent to the cleaned concrete surface, and after it is slightly dried, spread polymer mortar evenly on the pavement with a thickness of15 mm..
3.4 hollow slab treatment technology
Cracks and broken slabs in the course of pavement use are almost all related to slab bottom void [4]: even some slabs that were neither broken nor cracked at that time may still have slab bottom void, which is hidden, but its harm is very great. In pavement repair, if the void slab is not treated, even if the overlay reaches more than 20c, the occurrence of reflection cracks cannot be prevented.
4, the old bridge asphalt layer repair construction technology.
The asphalt overlay construction of the old bridge pavement is basically the same as that of the new highway asphalt pavement, and the main links in the construction are [3]:
1. Broken slab treatment: Dig out the broken slabs such as serious broken slabs, serious cracks and broken slab angles of the original pavement, and repair them with early strength concrete or early strength reinforced concrete until they are flush with the original pavement. The pavement of the original culvert cover plate should also be treated together;
2. Stabilize the original pavement slab: grout the hollow concrete slab soaked in mud and the slab with light and moderate cracks at the bottom of the slab to keep the concrete slab in a stable state. Long-term use, the original pavement base is a section with poor water stability such as lime soil, and the original concrete slab can be fully grouted.
3. Improve the waterproof ability of the original pavement: after all shrinkage joints, longitudinal joints and cracks are cleaned up, fill the joints with caulking materials. Then add 1.5 ~ 2.5 cm geotextile isolation layer or asphalt mixture isolation layer on the original concrete pavement, and sprinkle adhesive oil where there is no isolation layer to reduce the underwater seepage of the pavement and improve the bonding ability between the overlay and the original pavement;
4. Overlay asphalt layer: The overlay asphalt concrete on the isolation layer (adhesive layer) should generally be divided into two layers, the lower layer is thick (generally 4 ~ 8 cm), and the open graded coarse-grained or medium-grained asphalt macadam or asphalt concrete with good thermal stability is used, while the upper layer is thin (generally 2 ~ 9 cm thick), and the dense graded fine-grained or medium-grained asphalt concrete with good waterproof performance is used. When the cross slope of the original cement concrete pavement is small, the cross slope of the pavement should be adjusted according to the asphalt surface not less than 1.596. Only the upper deck can be paved, and the lower deck within 50m at both ends of the bridge head should be sloped.
The technical requirements, mixture ratio design, mixing and paving of surface raw materials are the same as those of conventional asphalt pavement construction. Only when rolling, the thickness of asphalt layer should be considered when selecting the tonnage of compaction machinery to prevent the secondary granulation of asphalt mixture caused by excessive vibration.
5. Summary
This paper mainly studies the repair of old bridge pavement from the aspects of bridge deck pavement evaluation, maintenance technology and asphalt overlay design. The main contents of this paper are as follows:
1, the evaluation of the original bridge is an important prerequisite for the bridge pavement repair work. The investigation contents and methods of old bridge pavement evaluation are expounded.
2. In the aspect of bridge deck maintenance, the crack treatment technology, staggered platform treatment technology, non-structural disease treatment technology and void plate treatment technology are studied.
3. In the aspect of construction technology, the construction technology of asphalt overlay on old bridge pavement is emphatically analyzed.
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