Simulation Study On Vacuum Compaction Mechanism Of Asphalt Mixture Based On Discrete Element Method

The mechanism of vacuum compaction has been studied from the microscopic perspective by using the discrete element method in this paper.Based on the basic principle of the discrete element method and the characteristics of PFC3 D,the properties of the asphalt mixture are analyzed.This paper worked out the modeling or expression methods to the components of asphalt mixture,in which we focus on the modeling methods and the algorithm in the application PFC3 D of the closed bubbles.Thus,this paper established the asphalt mixture's discrete element model which contains the closed bubbles.Based on the discrete element model of the incompact asphalt mixture,this paper simulated the mixture's compaction process,and monitored the dynamic changes of the whole material and the internal closed bubbles' mechanical property during the compaction process.The simulation results are consistent with the actual situation,which supported the feasibility of the numerical simulation and the accuracy of the discrete element model.Based on the discrete element model mentioned above,this paper simulated the compaction processes of asphalt mixture under the conventional conditions and vacuum conditions.According to the experimental results,the vacuum compaction process simulation was modified to obtain a more reasonable result.The simulation results showed that: Comparing with the conventional compaction,the vacuum compaction process have a larger settlement under the same load;and the closed bubbles in the vacuum compaction specimen were smaller,in other words,the vacuum compaction specimen has a lower porosity;vacuum environment not only can reduce the "gas spring" effect of asphalt mixture but also affect the quality of asphalt or the properties of aggregate-asphalt interface.In order to compare the difference between conventional and vacuum compaction,the uniaxial compression tests were carried out to the specimens under the two conditions.The test results showed that: the conventional compaction specimen's compressive strength is 1.68 MPa and axial strain is 0.0353;the vacuum compaction specimen's compressive strength is 1.72 MPa and axial strain is 0.0311.Comparing with the conventional compaction specimen,the compressive strength of the vacuum compaction specimen is much higher,while the axial strain is smaller comparatively.