Research On Recycling Method And Miscibility State Of Material Based On Old Asphalt Concrete Pavement

Asphalt pavement has suffered road damage due to a variety of factors in the long-term use process.It is facing severe renovation and reconstruction work.In this process,a large amount of waste old asphalt concrete is generated.Objects cannot be applied and are discarded and piled up or buried in the soil.In order to solve the waste asphalt concrete produced during the maintenance process in China,reduce the waste of non-renewable resources,and protect the ecological environment,this paper further studies on the basis of the design of the layered hot recycled asphalt mixture mix and road performance of the team of brother Zhao Shijing,Mainly from the three aspects of the layered recycled asphalt mixture miscibility status,recovery process and recovery equipment,the research content is as follows:(1)In order to more qualitatively show the difference of the miscibility status of the recycled mixture,according to the old asphalt participation in the regeneration method to distinguish the partial miscibility and complete miscibility of the recycled mixture,it is planned to use the extracted asphalt and the new asphalt miscibility to express the complete Miscellaneous state,the artificially separated old asphalt and new asphalt are heated and mixed to express part of the miscible state.By comparing the miscibility of the old and new asphalt in the recycled mixture,the influence of the mixed state on the performance of the recycled asphalt mixture is analyzed.The research shows that The miscibility of the old and new asphalt is the main reason for the difference in the performance of the recycled mixture.With the increase of the RAP content,the maximum increase rate of the optimal asphalt content of the upper layer completely miscible mixture can reach 2.2% compared to the partial miscible mixture.The lower layer can reach 4.5%.Although completely miscible recycled materials with stable performance and less variability have advantages in raw material costs,there are still differences in overall production costs,social and environmental benefits and other comprehensive benefits,which are not suitable for large-scale production.(2)Analyze the impact of the recovery method on the damage degree of the old asphalt concrete,compare the difference between the two recovery methods of manual separation and mechanical crushing on the old aggregate gradation pass rate,and the test found that the maximum change in the old material gradation pass rate of the upper and lower levels It is concentrated between 4.75～9.5mm,and the difference values are 8.1% and 22.7%,which shows that the "fine" phenomenon of large particle aggregates in the old material has seriously affected the design level of the mix ratio of the hot recycled asphalt binders.Based on this,combined with the current recycling process of old asphalt concrete,an optimized recycling equipment model for milling and crushing of old materials is proposed.(3)Orthogonal test was used to analyze the mixing factors of the blending status between virgin and aged binders.According to the New and old asphalt miscibility test,characterize the influence of mixing factors such as mixing time and preheating temperature of regenerated asphalt mixture on the degree of miscibility of virgin and aged binders,The degree of influence of different factors:the optimum mixing time > preheating temperature > preheating time > mixing temperature,And it is concluded that the optimal mixing combination recovery process of mixing time 90 s,preheating temperature 110℃,preheating time 4h,mixing temperature 180℃ has the best improvement in the miscibility of virgin and aged binders.(4)The Superpave design method was used to perform quantitative characterization tests on the miscibility of the virgin and aged asphalts in the partially miscible recycled asphalt mixture.The mixture of recycled asphalt with different RAP content(20%,30%,40%)and old material source levels was selected.The DOB quantitative characterization of the virgin and aged binders under the optimal mixing conditions.The research shows that the miscibility of the upper layer of reclaimed materials is 91%,84%,79%,and the lower layer is 95%,88%,82%.The degree of complete miscibility has been achieved,and the miscibility of the actual recycled asphalt mixture in the process is verified to be partially miscible.Therefore,this article recommends that the effective coefficient of old asphalt miscibility should be considered when designing the RAP material for hot recycled asphalt mixture.