| With the rapid development of the highway transportation industry,China’s highway has entered a large-scale maintenance period.The use of recycled asphalt pavement(RAP)has become one of the important ways to develop the green transportation industry in China.RAP has great variability due to the influence of various factors,among which RAP gradation has significant influence on the performance of recycled materials.During the milling process,the minerals are affected by the characteristics of the milling process,leading to the refinement of the RAP gradation,and then influence the stability of the performance of the recycled materials.Therefore,it is necessary to study the RAP variability in the milling process and reduce its variability with targeted methods,which has practical significance and value for improving the RAP utilization rate and guiding the regeneration production.This paper mainly studies the variability of the recycled asphalt pavement(RAP)milling process,as follows:(1)The discrete element method are adopted to simulate the process of old asphalt pavement milling planer,analyze the structure and mechanical strength of asphalt pavement.Use Unigraphics NX to establish three-dimensional model of the rotor of milling planer,use Bonding contact model,establish aggregate particle geometry based on Solidworks and use the EDEM for rapid filling.After building the asphalt pavement milling planer model,analyze the stress of asphalt pavement materials under the influence of the advance speed,milling speed and milling depth.(2)Different sources RAP due to the design and construction,and the influence of natural condition,its variability is difficult to control.In order to reduce the RAP variability from different source,the gradation was determined by performing extraction experiment on core samples of different road sections.And the gradation was quantitatively evaluated based on the maximum density curve theory and the fractal theory.Three different classification methods,adjacent clustering,decision tree classification and Fisher discriminant method are used to classify the eigenvalues,and the comparative analysis of the classification effect is carried out.The decision tree classification is determined as a method to reduce the variability of RAP from different sources,and the optimal classification area is defined.(3)Based on the milling principle of asphalt pavement,the RAP gradation under different types of mixtures and different milling speeds is evaluated,the discrete characteristics and distribution rules of aggregates are clarified.And the index of gradation change degree and agglomeration degree is proposed to analyze the RAP variability.And the influence of different factors on gradation was analyzed based on the maximum density curve theory.(4)In order to make a preliminary assessment of RAP gradation before road section milling and reasonably divide the range of milling speed,based on the analysis of RAP gradation thinning process at different milling speeds,a prediction model of RAP milling gradation is proposed and verified by laboratory tests.The results show that the prediction model of RAP milling gradation has certain reliability.Based on this refined prediction model and the core sample gradation,the prediction model can be used to estimate the gradation of RAP combustion at different milling speeds. |
