Construction technology of old asphalt concrete pavement?

This paper discusses the research on cold recycling technology and construction technology of old asphalt concrete pavement. Firstly, the principle and construction characteristics of cold recycling technology for asphalt concrete pavement are introduced. Then, according to many years of engineering experience, the control points of cold recycling construction technology of asphalt concrete pavement are discussed. It is hoped that the construction quality and level can be improved and the road transportation function of asphalt concrete can be fully exerted.

The cold recycling technology of concrete can reuse the damaged surface materials without wasting raw materials and reducing capital investment. In addition, it will not cause great damage to the surrounding environment. Therefore, compared with the traditional excavation construction method, the cold recycling technology of concrete asphalt pavement has greater advantages.

1 principle of cold recycling technology for asphalt concrete pavement

As early as the late 1980s, the application of cold recycling technology produced good benefits and was widely recognized by foreign experts, thus expanding the application scope. The technological process of this technology is as follows: firstly, milling and crushing the damaged pavement materials. Then, according to a certain proportion, the recycled additives and new aggregates are prepared and stirred evenly to form a brand-new material. Paving these materials on the pavement again, and then shaping and rolling the pavement, can restore the normal traffic function of the damaged pavement and have the same bearing capacity as the original pavement. Cement is usually used as an additive when cold recycling technology is applied. Among them, the dosage of cement is mainly determined according to the actual dosage of the project. There are two ways to add cement: one is to spray cement on the road surface that needs regeneration by mechanical or manual methods.

Secondly, cement and water are mixed together to form cement slurry. And then mixed with the mixture in a cold regenerator. These two methods have their own advantages, but they also have some defects. Specifically, the advantage of the first method is simple operation and easy control of the cement control beam. The disadvantage is that in the above process, it is easy to produce a lot of dust. The advantage of the second method is that there won't be much dust when adding cement. However, it takes several stages to finish the milling of the whole road surface by this method. So after all the processes are completed, the recycled pavement can be rolled. In this case, it will lead to different working faces on the road surface. In the final rolling, the water content of the operation section is different because the interval is too long. If the same amount of water is added in advance, the water content in different parts will be different in the final rolling process.

2 cold recycling construction characteristics of asphalt concrete pavement

According to the actual engineering construction experience, it can be seen that the cold recycling technology of asphalt concrete includes the following characteristics. First, the damaged pavement materials can be reused, which reduces the cost of raw materials and shortens the technological process. Damaged materials are effectively treated without polluting the environment; Secondly, after adopting the pavement cold recycling technology, the workload is reduced, the construction period is shortened and the project cost is saved; Thirdly, after continuous actions such as mixing, paving and rolling, the new aggregate is more closely combined with the old paving material, ensuring the smoothness and compactness of the repaired pavement; Fourthly, after the application of cold recycling technology, various transverse cracks on the old pavement are eliminated. It has strong applicability to any damaged road surface; Fifthly, after the cold recycling technology is adopted, the bearing capacity of the repaired pavement is enhanced and the road performance is higher; Finally, the cold recycling technology can break the surface layer and the base layer at the same time, and will not cause great damage to the subgrade.

At the same time, it will not cause great influence on subgrade. And the integrity of the pavement is ensured. It is worth noting that the cold recycling technology is still in the development stage and not fully mature. Therefore, in the process of application, there will inevitably be some defects. First, cold recycling technology is more suitable for repairing low-grade asphalt concrete pavement. However, for expressway, due to the high quality of the original asphalt concrete pavement materials, the quality of cold recycling can not meet the quality requirements of higher asphalt layer, which ultimately reduces the utilization rate of this new material. Secondly, for high-grade highways, the pavement elevation will be determined after the completion of the new road. So do most cities. Once the pavement elevation is determined, it will not be adjusted basically. In this way, when laying a new surface layer, it will be restricted. Therefore, cold recycling technology is not suitable for repairing high-grade highways or places limited by altitude.

3 asphalt concrete pavement cold recycling construction technology control points

Take an asphalt concrete highway project as an example, which was built in August of 20 10. With the increase of vehicles, the burden on the pavement becomes heavier and heavier, resulting in pavement damage. In this case, it not only affects the normal traffic operation, but also lays a huge safety hazard. In order to solve the above problems, we decided to adopt cold recycling technology. According to the actual engineering experience, the specific construction points are discussed below.

3. 1 construction preparation

Comprehensive preparations should be made before construction to ensure the quality of the project. 3. 1.65438+ After all the equipment is in place and successfully debugged, the smooth development of the construction work can be guaranteed. The model of this road repair and cold regeneration is WR2500. 3. 1.2 Requirements for construction materials After the original pavement damaged materials are broken, the new materials obtained are cold recycled fillers. At this time, the specifications of material particles should be strictly controlled. According to the regulations, the particle size of 45% ~ 65% should exceed 4.75 mm, otherwise, the corresponding aggregate should be added to fill it. In addition, when selecting materials, portland cement with high strength and low water-heat ratio is usually selected, which can enhance the effect of the mixture.

3.2 Construction process flow

In cold recycling construction, we should strictly follow the relevant procedures to ensure that the construction quality of each link meets the requirements and there can be no mistakes. 3.2. 1 Thoroughly clean the road surface. First of all, before the construction, the debris and garbage on the road surface should be thoroughly removed. Then, according to the requirements of road design, carefully measure to ensure compliance with construction standards. In addition, traffic should be completely closed before construction. In the construction work area, no other vehicles are allowed to enter the site except construction vehicles. 3.2.2 When paving cement, manual operation shall be adopted. Calculate the required cement consumption per unit area according to the percentage of the original design cement consumption.

3.2.3 Material Crushing and Grading Control In the construction, the crushed materials of the old pavement must be fully crushed. There are usually two ways to do this. On the one hand, when grinding broken materials, the speed should be controlled within a reasonable range, generally 6 ~ 8m/min. If the original pavement is seriously damaged, the milling speed should be reduced appropriately. On the other hand, the speed of cold regenerator should be controlled within a reasonable range, and the general outlet speed is 150r/min. In addition, in the milling process of cold recycling machine, the broken beam pressure should be controlled reasonably, and 6Bar is generally appropriate. In addition, in order to avoid unreasonable mixture matching, it is required to carefully check the mixture mixing of cold recycling machinery during milling operation.

3.2.4 Leveling of mixture When leveling the road surface, the roller bulldozer must operate in strict accordance with the requirements to prevent quality problems caused by poor compaction. Especially for materials with low plasticity, it is necessary to control the water content of the mixture to avoid lateral displacement. 3.2.5 Maintenance of cold recycled pavement After the pavement construction is completed, water will be sprayed in time for maintenance to avoid cracks caused by drying. In general, the curing time should not be less than 8h. In case of rainy days during construction, old materials should be piled up. At the same time, it should be dried in time to prevent deterioration.

In recent years, due to the gradual damage of old asphalt concrete under the action of external force, the proportion of pavement repair has increased. But it also promotes the development of cold recycling technology. This technology belongs to the initial stage of application, which has advantages and disadvantages. Therefore, the technical points must be strictly controlled in the construction process to avoid quality problems. Taking a project as an example, this paper discusses the application of cold recycling technology in detail. For example, when implementing this technology, we must strictly control the quality of materials, the compactness of rolling and timely maintenance. I hope it can play a reference role.

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