Discrete Element Simulation On Old Pavement Milling Based On The Aging Characteristics Of SBS Modified Asphalt Mucilage

Nowadays,China has completed all levels of highway asphalt pavements of more than one million kilometers according to the mileage of lanes.Among them,SBS modified asphalt pavement occupies a large proportion.A large number of asphalt pavements needs to be repaired and maintained every year,and the milling operation is a key link in the large and medium scale repair of the asphalt pavement.Faced with the increasing scarcity of stone resources,as well as the rapid growth of the pavement milling operation,how to improve the regeneration of pavement milling material utilization rate,improve pavement milling operation efficiency,has become the focus of widespread concern in the industry.Ideally,the milling should make coarse aggregates split from asphalt mucilage as many as possible,and meanwhile,it should avoid broken stone materials and large lumps.However,current milling machines adopt the same milling operations on different old asphalt pavements,which results in a waste of resources and energy consumption.Therefore,it is necessary to systematically study the pavement milling process with different binder and different aging degree.With respect to the existing problems in traditional milling method,through the research on aging rules of SBS modified asphalt mucilage,it is concluded that there is a big difference in aging properties of SBS modified asphalt mucilage with different service life.Therefore,targeted research shall be carried out on the milling process of pavements with different service life.Uniaxial compression is carried out with the use of prepared test specimen of modified asphalt after aging,and three-dimensional asphalt mixture specimen model is established with the use of Discrete Element Software PFC to carry out uniaxial compression simulation test in order to check the model parameter.On the basis of checked model parameter,discrete element model for simulating the milling process is established.By setting different cutter parameters,the simulation of old pavement milling process is carried out respectively to explore the best cutter parameter.Under the cutting-tool size and AC-16 gradation used in this research,the result shows that there is a strong fluctuation of the forces on the tool in the milling process,of which the maximum stress may appear in any direction of X,Y and Z.The cutting speed and cutting depth have a great influence on the cutting force,while the cutting angle has no significant influence.In addition,when milling the old asphalt pavements that have been used ten years or so,for lower cutting force,the 0.5m/s cutting speed,the 20 mm cutting depth and the 45 degree cutting angle are better.Besides,they shall avoid milling operations using parameters of 1m/s cutting speed,40 degree cutting angle and 25 mm cutting depth in order to avoid large lumps.