The Study Of The Effect Of Coarse Aggregate Of Microstructure Characteristic On The Performance Of Asphalt Mixture

With our country`s increase of traffic volume, traffic axle load, we make higher demandof the asphalt pavement.In order to ensure the quality of the pavement,improving the basicperformance of the material is a critical factor. In the past, scholars have often simplyconsidered that improving the performance of the asphalt binder can enhancing all theperformance of mixture. Consequencely, extensive use of modified asphalt and even importedmodified asphalt increase pavement’s cost crazily. In order to get rid of the trouble, peopleincreasingly concerned about the aggregate which account for more than90percent of thevolume of the asphalt mixture. To research the aggregate, it consist of the graduation andmorphological characteristics of the aggregate. In the world, many scholars have study thegraduation of the aggregate and made achievements, at the same time, they have obtainedseveral appropriate graded type for different pavement. However, there is little study aboutthe morphological characteristics of the aggregate.In view of this research status, the subject first conduct comprehensive analysis of avariety of testing methods of morphological characteristics of the aggregate at home andabroad, meanwhile we study the aggregate imaging system AIMS, a foreign development ofan experimental method. By analyzing the different parts of aggregate, and aggregates ofdifferent particle size shows that the aggregate of the different regions have their ownmorphological characteristics, and in actual highway projects we should use themcarefully.Meanwhile with the decrease of fine aggregate`s particle size, the angular graduallyreduced.When the particle size is0.03mm,the angular is pessimal,and gradually increasedafterwards.However, with the decrease of fine aggregate`s particle size, the angular graduallyincreased.When the particle size is4.75mm,the aggregates is the most irregular,and it has themost abundant angular status.The four different kinds of aggregates,including16mm,13.2mm,9.5mm and4.75mmwere worn0,600and1200times respectively with the Los Angeles abrasioninstrument.Finally,there were12kinds of aggregates which belong to different abrasion timesand different particle sizes.Afterwards, image acquisition and processing was conducted withthe MASCA system developed by oneself. Seven morphological characteristics of quantitative indicators,which included axial coefficient, convexity, roughness, angularityparameters, roundness, fractal dimension and sphericity,were proposed. After analysis of thevarious indicators of the different particle sizes and different wear state, with the increase inwear intensity, the coarse aggregate particles gradually became smooth and round, convexitybecome larger, the angular parameters, roundness and fractal dimension reduced. Thespherical index value increases and was close to1, these trends are consistent with thechanges of each index formula and special graphics.When the particle size were from4.75mmto16mm,with the size increased, the shape is smoother. Compared with the previous analysisof AIMS, the conclusion was the same. According to the variance analysis between the weretimes and the various indicators, the fractal dimension had the highest correlation with thewear numbers.The shape, roughness and surface texture of the aggregate particle, determines thelocation and the state of the interaction between particles in the mixture after compaction,However these changes would directly make change of the asphalt mixture performance, sothe study associate quantitative indicators of the particle shape with the specific asphaltmixture performance, in this way we can utilize the links to guide to the actual projectscientifically. To research the above-mentioned in this topic,3kinds of the Marshall specimen(AC-16, SAC-16and SMA-16) was manufactured by adotpting the coarse aggregate which is0,600and1,200wear times in three different condition, and compare the different mixture ofMarshall volume index and mechanical index. And select high-temperature rutting test,penetration shear test and the new round indenter penetration test to evaluate the hightemperature shear resistance and the shear ability of different gradation and different wearstate in the same experimental conditions.From the experimental results, a good correlationbetween each test, the coarse aggregate surface texture rougher, more angularity, hightemperature shear capacity of the stronger， this effect for different gradations have similarchanges. Just for this AC-intensive with the asphalt mixture, when the coarse aggregate shapechange to a certain state, the aggregate change in its change caused by the mixture is nolonger obvious, and for the SAC and SMA the coarse aggregate content intermittent gradingmore than70per cent, change the status of the aggregate mixture property than intensive withmore intense. Finally, for this article selected level with coarse aggregate of fractal dimension of each particle size correlation of the various high-temperature indicators, and ultimately theactual project should focus on the control of aggregate particle shape parameters.