RAP Recovery Process And Research On The Key Factors Affecting Of Hot Recycled Asphalt Mixture Performance

During the long-term using process of the asphalt pavement, under the impacts of traffic load and natural factors, asphalt aging and aggregate refinement will degrade the service performance of asphalt mixture, which will finally result in various pavement diseases. China’s highways are confronted with a large amount of repair & maintenance tasks. To handle a large number of waste asphalt mixtures produced during the overhaul of highways, save resource consumption and preserve the ecological environment, this paper has made a research in hot mix plant recycling of waste asphalt mixture.This paper has carried out a systematic research in RAP grading variability of cold milling & planing recycling technology and influence factors of pavement performance of the recycled asphalt mixture. Above all, the paper has proposed the best milling & planing mode for old asphalt mixtures through the analysis on grading variability of the RAP recycled through different milling & planing technologies. It has carried out breaking, screening and grading treatment for RAP in combination with the analysis on asphalt content and grading variability, verified the effects of breaking and screening of RAP on variation control, and made a comprehensive evaluation on RAP performance through centrifugal separation test and screen test to detect the asphalt content in RAP materials, make an analysis on asphalt aging, conduct mineral aggregate gradation, etc.In addition, aiming at different functional requirements of different layers of asphalt pavement on asphalt mixtures, the paper has carried out mix design for recycled asphalt mixture with the gradation of AC-20 and ATB-25 and RAP mixing amount of 20% and confirmed the recycling gradation and optimal asphalt content. It has carried out an analysis on the influences of four factors- RAP mixing amount, RAP particle size, addition of recycling agents and recycling technology on the high-temperature property, water stability property and low-temperature property of recycled asphalt mixture through tests. The test results show that(1) along with the increase of RAP mixing amount, the high-temperature property and water stability property of recycled asphalt mixture also increase, while the low-temperature property decreases;(2) with the same RAP mixing amount, the influence of RAP particle size on the property of recycled asphalt mixture shows the following rule: as to high-temperature property, 5~10mm>10~16mm>0~5mm; as to water stability property, 5~10mm > 0~5mm > 10~16mm; as to low-temperature property, 0~5mm > 5~10mm >10~16mm; through comprehensive consideration, it’s suggested to give priority to the use of RAP materials of 5~10mm in actual application;(3) though the addition of recycling agents can improve the void volume of recycled asphalt mixture, it will decrease the high-temperature property and water stability property of recycled asphalt mixture;(4) indoor RAP asphalt mixture recycling technology confirmed by this paper shall be as follows: add recycling agents to the preheating RAP directly and mix them for 210 s. The recycled asphalt mixture produced by mixing with preheating temperature of RAP of about 110℃ will have the best pavement performance.Finally, the production mix design is carried out for the test road section, so as to build a test road which shall satisfy the requirements of road standard on the performance, and make an evaluation on economic and social benefits of the recycled asphalt mixture.