In China, asphalt pavement accounts for a large proportion in high-grade and secondary roads, so nearly 10% of asphalt pavement needs to be renovated every year, and the total amount is expected to reach more than 2 million tons. Poor treatment will pollute the environment and waste the material itself.
In this case, how to reuse the original asphalt pavement is worth our in-depth study. Through comprehensive tests, we think that cold recycling of asphalt is a good choice.
According to data analysis, the recycling rate of pavement in major developed countries in the west reaches or even exceeds 80%, while countries such as the Netherlands and Belgium can even achieve 100% complete recycling; Due to the lack of energy, Japan has always attached great importance to pavement recycling technology. Since 1976, the recycling rate of pavement waste has exceeded 80%. Relatively speaking, the recycling technology of asphalt pavement in China is not mature enough.
In recent years, with most of China's high-grade highways entering the stage of overhaul and reconstruction, and the country's emphasis on energy conservation and environmental protection, the recycling of waste pavements has been highly valued by people.
Cold recycling technology of asphalt pavement refers to a series of working processes, such as continuous milling, crushing, adding recycled materials, cold recycling at room temperature with special machinery, mixing, paving and rolling. So as to form a structural layer with certain bearing capacity. Compared with hot recycling technology, cold recycling technology saves energy and resources, makes full use of old asphalt mixture, prolongs the construction season, improves the working conditions of construction workers and reduces environmental pollution, so cold recycling technology is more in line with the current social needs.
As mentioned above, cold recycling technology has a good development prospect, but there are many technical difficulties in the utilization and production of asphalt pavement. For example, after asphalt pavement is used for a period of time, due to the ultraviolet irradiation of sunlight, the surface binder gradually ages and hardens, and the adhesion with aggregate decreases. Therefore, the old asphalt pavement material needs to add a certain amount of new binder, that is, stabilizer, which can make the original surface material form a new whole as the structural layer of the pavement. Therefore, the choice of stabilizer is particularly important.
Foamed asphalt is a good stabilizer. By stabilizing foamed asphalt, the strength, stability and durability of the material can be improved. Foamed asphalt structure layer has no volatile matter during construction, which is more environmentally friendly and less affected by seasons and climate. The early strength of foamed asphalt structure layer increases rapidly, and it can be opened to traffic immediately after construction. Therefore, foamed asphalt is a good choice among cold regeneration stabilizers.
However, considering other issues such as funds, cement is now used as a stabilizer. A large number of repeated tests show that when the proportion of base is 50: 50 and the cement content is 6%, its strength is greater than 2.5MPa, which can well meet the requirements of "Code for Construction of Base" for highway base strength. However, with the decrease of the amount of old materials, the 7-day compressive strength increased, but the increase was not significant; Moreover, the influence of the amount of old materials on the strength of 28d is less, or even almost no influence. Therefore, it is not impossible for the utilization rate of old materials to reach 100%.
Cold recycling construction technology and technology: spreading cement and aggregate in advance; Milling and mixing the old pavement, and adding water to mix; Stable voltage; Leveling; Rolling; Stay healthy. Among them, the health maintenance work is completed by special sprinklers, and the sprinkling requires that the road surface be wet. The curing period is 7 days. Roads should be closed during maintenance, and traffic should be properly opened after maintenance to enhance the bond between structural surface and asphalt concrete surface.
The specific operation steps are as follows:
1. Placement of cement
According to the calculation results, put the vertical and horizontal spacing of cement and spread the cement evenly. Pay attention to the equal paving area of each bag of cement. After the cement is paved, there should be no blank position on the surface, and it should not be excessively concentrated. The mixing speed and paving time of cold recycling machinery should be well coordinated, and mixing should be carried out as soon as possible after paving cement to ensure the continuity of construction.
2. Cold recycling machine grinding and mixing
(1) Pushing a waterwheel cold recycling machine to walk on the original road surface. Generally, the walking distance is controlled at 6m/min- 12m/min, which can well ensure that the gradation fluctuation of milling materials is not large. In areas with serious network cracks, the speed of the recovery device should be appropriately reduced to increase the speed of the grinding rotor.
(2) The regeneration device should be followed by professionals, so as to check the regeneration depth at any time, and the water content should be adjusted according to the regeneration. The depth inspection is based on the adjacent reclamation or original pavement, and the penetration depth is measured with a steel drill to check whether the depth is qualified.
(3) During multi-knife construction, always pay attention to the lap width to ensure its width, and the adjacent knives overlap 10-20cm for mixing to ensure no knife leakage.
(4) 4-5 people should be arranged to handle the sideline, clean up the impurities in the mixture and the scraps at the starting position of each knife after the recycling machine, which can well reduce the flatness and compactness of the vertical and horizontal joints.
(5) Regenerator with screed should be checked frequently to ensure the thickness of mixture.
(6) The length of each regeneration is based on the principle of ensuring the normal operation after reading, and the construction is carefully organized to make the regeneration length as long as possible to reduce the horizontal joints. The primary regeneration length is 150m-200m.
(7) Check whether the unit is damaged after each regeneration. If it is found to be damaged, replace it immediately.
3. Rolling and forming
Because the asphalt material is screened from the original pavement and recycled mixture is added, the thickness of the base should be appropriate, otherwise it will easily lead to the instability of pavement asphalt performance. According to the requirements of recycling specifications, the thickness of cement recycled asphalt pavement should be less than 220mm, so the rolling should be carried out according to certain standards. Therefore, during construction, the static pressure should be 1 time and the vibration should be 4 times to ensure the overall stability of the mixture.
4. Maintenance
After the rolling test, the water shall be maintained for not less than 7 days, and the water shall be sprayed evenly.
5. Quality management
In-situ continuous cold recycling construction of asphalt pavement shall conform to Technical Specification for Highway Asphalt Pavement Recycling (JTG F4 1-2008).
Under the national conditions of sustainable development in China, people pay more and more attention to cold recycling technology. Cold recycling technology can not only improve the grade of asphalt pavement in a short time, but also be realized under the existing economic conditions in China. Therefore, cold recycling technology is expected to be widely popularized in China.
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