Evaluatiing The Load Sensitivity And Permanent Deformation Of Hot-recycled Asphalt Mixture

Rutting is one of the major failures of asphalt pavement, and it severely influences the comfort of driving. It is still a long way to take further study on rutting of asphalt pavement, especially for hot recycled mixture of asphalt pavement. This paper provide new test, which was conducted at the temperature of 60? under multiple stresses determined by a simplified axle load spectrum considering the pavement management system (PMS). This optional multiple repeated load (OMRL) test, capable of simulating the axial load spectrum in real pavement, was developed to evaluate the rutting susceptibility of asphalt mixture. Five kinds of asphalt mixtures were used to characterize high temperature performance compared with others, including virgin mixtures with two kinds of asphalt and three kinds of hot recycled mixtures with different contents of RAP. The new test and its indexes proposed in this paper were aimed to give a reference to the establishment of the evaluation system and performance limits for hot recycling asphalt mixture.Firstly, this paper studied the properties of RAP. The asphalt-aggregate ratio and gradation of aged asphalt mixture were obtained from extracting method. Then, the performance of the aged asphalt from reclaimed method was tested. After that, Mashall mixuture design method was used for the five types of hot recycled mixture with different contents of RAP.Secondly, in order to obtain accurate data of the axial toad, PMS was used for data collection. Four kinds of stress level were determined after representative values of a toad were calculated. Then an optional multiple repeated load (OMRL) test was established after the initial and terminal conditions of the experiment as well as performance test index being determined. The newly proposed test indexes are lowest average strain rate (LASR), multiple flow number (MFN) and the curve of permanent strain rate versus stress level, which could evaluate the rutting resistance of asphalt mixtures under a more realistic loading condition. Overall, this OMRL test provides a better understanding of the rutting behavior of asphalt mixtures to improve the mix design and field performance while it saves much time in comparison with the origin repeated permanent load deformation (RLPD) test.Thirdly, confining pressure and temperature were taken into consideration as a factor that could influence anti-rutting performance of asphalt mixtures. Ultimately, the experimental conditions were determined with 60? and 0 kpa confining stress.Finally, the OMRLtest was conducted to evaluate high temperature performance of virgin mixtures with two different types of asphalt (PG76-22 and PG70-22) as well as hot recycled mixtures with different contents (30%,50%,85%) of RAP, and the dynamic modulus test was conducted as a reference. From the test results, the high temperature performance of hot recycled mixture of asphalt pavement with low contents (30%) of RAP is close to the virgin one, while with the increase of RAP content, the characterization of mixture approaches to RAP, which is harder and more brittle than virgin ones. Due to these above, the dynamic modulus is not suitable for high temperature performance of hot recycled mixtures any more.