Research On Performance Degradation And Pavement Structure Response Characteristics Of Hot Recycled Asphalt Mixture

The plant-mix hot recycling technology can recycle asphalt pavement materials and has been widely promoted and used in highway maintenance and construction projects.However,according to actual observations,compared with ordinary asphalt pavement,recycled asphalt pavement has a faster crack development speed in actual use,which leads to the fact that the actual service time of recycled asphalt pavement does not meet the design requirements.In order to improve the crack resistance and fatigue resistance of recycled asphalt pavement and increase the service life of recycled asphalt pavement,based on the key technology project of thermal regeneration in Shanxi Province.The gradation of asphalt mixtures in each grade and the optimal asphalt dosage were determined through the design of the mixture ratio of thermally recycled asphalt mixture in this paper firstly.Then the high temperature stability and low temperature crack resistance of thermally recycled asphalt mixtures with different RAP contents were analyzed by uniaxial dynamic compression modulus test,rutting test and semicircular bending test,according to the results of the laboratory test,the optimal RAP content of the thermally recycled asphalt mixture was determined by the performance balance design method,and the rutting test data was fitted by the permanent deformation viscoelasticity model of the asphalt mixture,and the corresponding physical parameters were obtained,which can predict the permanent deformation of the thermally recycled asphalt mixture under repeated loads.Then,the simulated water temperature aging test was carried out on the hot recycled asphalt mixture with the optimal RAP content by using the life cycle analyzer.The freeze-thaw splitting test,dynamic creep test,simulated rutting test,low-temperature semi-circular bending test and repeated load semi-circular bending test were carried out on the mixture with different simulated aging time to explore the decay laws of water stability,high-temperature stability,low-temperature crack resistance and fatigue resistance of recycled and fresh mixture under different aging time.Finally,the mechanical response of the two asphalt pavement structures was studied by finite element numerical simulation method,and the influence of the performance decay of the mixture before and after aging,the axle load and the thickness of the recycled layer on the crack resistance and rutting resistance of the thermally recycled asphalt pavement was analyzed.The main conclusions obtained are as follows:(1)The old asphalt in RAP is seriously aged,and new asphalt needs to be added for blending.All physical indicators of the old aggregate meet the specification requirements;the content of old asphalt in RAP is determined to be 4.5% by the combustion method,and then the Marshall mix ratio design method is used to design the gradation of recycled material with different RAP contents and the optimal amount of asphalt was determined.(2)The rutting factor and fatigue factor of the uniaxial dynamic compressive modulus test,the dynamic stability of the rutting test,and the fracture energy of the semicircular bending test are used to determine the high-temperature stability and lowtemperature crack resistance of recycled materials from the perspectives of mechanical properties and simulation respectively.A comprehensive analysis of the properties of the recycled material was carried out,and it was concluded that with the increase of RAP content,the high-temperature stability of the recycled material increased and the low-temperature crack resistance decreased.According to the performance balance design method,the optimal RAP content of AC-13 thermally recycled asphalt mixture is determined to be 35%.(3)The life-cycle analyzer is used to simulate the actual application environment of recycled asphalt pavement.The key parameters corresponding to the one-year simulated aging time of the full-life analyzer were calibrated according to the climatic conditions and traffic volume in Shanxi Province.The test results showed that under the simulated aging effect of 4 months,the decay rates and amplitudes of the water stability,high-temperature stability,and fatigue resistance of recycled materials and new materials are different largely,and the decay rates of the two approach gradually under the effect of long-term aging;the decay range of the low-temperature crack resistance of the recycled material is close to that of the new mix under the simulated aging of 4 months,and the decay rate is gradually larger than that of the new material under the long-term aging.(4)The ABAQUS model of the asphalt pavement structure was established,and the influence of the performance decay of the mixtures before and after aging on the key indicators such as the vertical compressive stress,vertical displacement,and transverse normal stress of the two asphalt pavements was calculated,and the surface deflection values of the recycled asphalt pavement under different axle loads are obtained.the rutting resistance and crack resistance of the aged recycled asphalt pavement can be improved by changing the thickness of the recycled layer,thereby achieving the purpose of improving the service life of the recycled pavement.The results show that the anti-rutting performance and anti-cracking performance of the asphalt pavement with the recycled layer are better than that of the fresh asphalt pavement;the long-term aging effect on the anti-rutting performance and the anticracking performance of the recycled asphalt pavement is much greater than that of the fresh asphalt pavement.The size of the axle load has a significant impact on the development of rutting on the recycled asphalt pavement,and the surface deflection of the recycled asphalt pavement increases linearly with the increase of the axle load.Compared with the standard axle load,the maximum deflection of the road surface increases by 1.247 mm under the action of the 260 k N axle load,and the increase rate reaches 149%.According to the decay characteristics of recycled material,the recommended combination of asphalt layer thickness for recycled asphalt pavement is4cm+8cm recycled layer+8cm,which is the reasonable combination thickness of the asphalt layer in this paper.