Experimental Study On Mesoscopic Characteristic And Permeability Of Asphalt Mixture Under Cyclic Loading

The early water damage of asphalt pavement is becoming increasingly serious and widespread:Under the dynamic action of vehicle load,surface water penetrate and remain in the pavement structure along the gaps and fissures of the pavement,and the repeated action of traffic load aggravate pavement materials damage;futhermore,the continuous damage of pavement materials make it easier for surface water to penetrate into,and asphalt pavement is under the influence of multi-field coupling of load-seepage-damage,and the permeability changes with the development of internal damage of road surface.Based on this background,with the aid of the CT scanning technology and the test system of permeability,which is developed by research group,under the multi-field coupling condition,the micro-characteristics and permeability changes under cyclic loading,aiming at the AC-13 and AC-20 mixture,are studied in this paper.The main results are as follows:(1)Comparative analysis of the relationship between compaction effort with voidage in two molding methods of asphalt mixture specimen.The results show that the voidage decreases with the increase of compaction effort,different molding methods of the same kind of material to obtain similar voidage,the rotation compaction times less than the number of the proctor compaction.(2)The triaxial compression tests are conducted on the permeability measuremet system and MTS test platform.It reveals that the main failure form of AC asphalt mixture under triaxial compression is flow failure,and the fatigue process is divided into different stages according to the characteristics of the axial compression displacement with the number of loading.(3)Using DIP technology to obtain the internal mesoscopic characteristics of asphalt mixture at different damage stages,the change of damage variable with cyclic loading and the void mesoscopic characteristic parameter,such as the voidage,the void number,the average equivalent diameter,and the roundness of the voids,are analyzed.The results show that the internal voids of rotating compaction molding specimen at the initial state presents a trend of large-middle-and-small-end,and there is no significant characteristic in the distribution of proctor compaction molding specimen along the height direction.The voidage,the average equivalent diameter and the roundness of the voids decrease with the increase of loading times,and the number of voids increases with the increase of the number of loading times,and the increment at the middle part is more relatively obvious than two ends.Aiming at the AC-13 and AC-20 asphalt mixture,regardless of the rotation compaction molding or proctor compaction molding,the damage variable of the specimen,increase with the increase of the number of loading.(4)Using the permeability test system under multi field coupling conditions,the permeability of different stages under different test conditions are tested,the effects of molding method,maximum nominal particle size,void ratio,axial pressure and water pressure on permeability are analyzed,and the relationship between permeability coefficient and damage variable are also analyzed.Under same voidage,permeability coefficient of rotating compaction molding specimen is less than permeability coefficient of proctor compaction molding specimen,the permeability coefficient increases with the increase of maximum nominal size,voidage and axial pressure,and the permeability coefficient and the pressure has a negative exponential relationship.The change law of permeability can be explained from mesoscopic damage variable and void change in mesoscopic.