Research On Technical Performance Index Of Warm Mix Asphalt Based On Fractal Theory

As a new kind of mixture, Warm Mix Asphalt has the vital significance to reduce the emission of Carbon Dioxide and other gaseous pollutant in road construction. Traditionally, the evaluations for Warm Mix Asphalt are mostly macroscopical, such as voidage, stability, flow value, dynamic stability and other indexes, however, they all have their own shortcomings when used to evaluate the performance of the mixture. Asphalt mixture, as a three-phase combination of aggregate, asphalt mortar, interspace, its macro-performance and microstructure are inseparable. The paper starts with the study of the fractal characteristics of aggregate, testing the macro performance of Warm Mix Asphalt and studying its microstructure as well, to give some micro indexes to evaluate Warm Mix Asphalt and try to establish the relation between micro and macro evaluation indexes.This paper selects the skeleton dense type gradation SMA as study object, under the compaction temperature150℃, respectively using the Marshall compaction method, rotating compaction method, wheel grinding method, to mold. Step the using aggregate before molding, then study their fractal characteristics. After molding, test the macro performance index of Warm Mix SMA, such as voidage, stability, flow value, freeze-thaw splitting strength ratio, dynamic stability etc., and obtain the microstructure image of Warm Mix Asphalt at the same time. Using related software to process the microstructure image of Warm Mix Asphalt, then obtain its micro index of evaluation. Finally, study the macro and micro evaluation index of Warm Mix Asphalt, search for the connection between them.The study show that the fractal value of aggregate is inversely proportional to its area, the larger the area of aggregate is, the smaller the fractal value does. Secondly, the scale-free range of aggregate is limited, there will be a significant change beyond a certain range for the fractal value of aggregate. For different rock aggregates (limestone and basalt), they have the similar fractal feature.For the Warm Mix Asphalt SMA, the macro performance is closely related with its voidage. With the change of the compaction times, the voidage is different at the same time, the corresponding macro performance is also different. When the compaction times reaches a certain number, the increasing number will play a tiny role in improving the macro performance of the Warm Mix Asphalt. For the microstructure of Warm Mix Asphalt, its voidage fractal dimension value will increase with the increasing compaction times, however the increase rate will be smaller and smaller. There is a positive linear corelation between the macro performance and the micro voidage fractal dimension value of the Warm Mix Asphalt, while the voidage fractal dimension value increases, the macro performance increases.