Research On Warm-mixed Recycling Technology With High Proportion Of Recycled Asphalt Pavement

With the regression of the peak of highway construction at home, more and more asphalt pavements need to be maintained and repaired. Recently, the hot-mixed recycling technology is used extensively in the maintenance and repair market of asphalt pavements, but the development of this technology is restricted due to the low proportion of recycled asphalt pavement (RAP), high temperature of new aggregates, secondary heat aging of RAP and the serious phenomenon of adhering cylinder wall in the process of mix and compaction. Although the cold recycling technology can make use of high proportion of RAP and has the advantage of low production temperature, this technology can not produce the mixture with excellent road performance. The warm-mixed recycling technology, the combination of hot-mixed recycling technology and warm-mixed technology, can produce the mixture with excellent road performance and enhance the proportion of RAP. Warm-mixed recycling technology is coincidence with the advocation of energy conservation, emission reduction, low carbon and environmental production. This technology will be inevitably studied, prompted and applied as a new type of energy conservation and environmental technology.Firstly, the basic properties of raw material are tested. We choose two types of warm agents, Sasobit and Evotherm, both of them are commonly used in the market. The warm-mixed mechanism of two agents are analyzed. We found that the Abson Method recommended by the norm has the problem that trichloroethylene solvent cannot be evaporated completely, so we proposed a more reliable method to recycle asphalt which is named as Modified Abson Method. The RAP material variability produces bad effect on the road performance of warm-mixed recycled asphalt mixture (WRAM). The variability can be controled through the heating, crushing, screening process indoor. The effect of the heat time of RAP on the variability is studied.Secondly, because of the inadequate blend between aging asphalt and original asphalt in the microstructure, the proportion of effective asphalt content is decreased. If we choose the optimum asphat conten which is determined by the traditional Marshell Test Methold of hot-mixed asphalt mixture to produce WRAM, we can found that a lot of new aggregates can not be covered by asphalt, so we propose that the optimum asphalt content of WRAM should be enhanced to some extent, which is still satisfy the request of standard. Meanwhile, the methold based on composite curve of viscosity-temperature can not be used to determine the mixing temperature, so that we propose to use the Marshall Test Method, which is compacted in different temperature. The RAP and warm agent can lead to the decrease of low temperature performance of WRAM, so that the performance even cannot meet the norm. Through four factors and six levels uniform design method, we determined the optimum mixing and curing technology by the standard of low temperature performance. We use this technology to produce WRAM and carry out the road performance tests, in which the percentage of RAP is 42,52, and 57. The results indicate that the determined optimum technology significantly improved low temperature performance and other road performance, but different kinds of warm-mixed additive and RAP proportion have different effect on these performance.Thirdly, we choose different size range of RAP and raw aggregates to simulate indoor experiment. After cooling, RAP was selected to do stage dissolution experiment, which can dissolve the asphalt covering the aggregates in three layers. The diffusion between aging asphalt and original asphalt was researched with Infrared Spectroscopy. The results indicate that the diffusion of aging asphalt and original asphalt is insufficiency.At last, the research results indicate that we can ultimately improve the road performance of WRAM and the proportion of RAP through the combination of hot-mixed recycling technology and war-mixed technology, the strict control of raw material’s performance and the selection of appropriate mixing and curing technology. However the highly sensitive degree of fatigue life to stress level is the key factor to constrain the proportation of RAP.