Research On The Characteristics Of Voids In Asphalt Mixture Based On Fractal Theory

Asphalt mixture is a kind of high strength composite material which is composed of coarse aggregates, fine aggregates, asphalt and admixture. It has developed mechanical system with a certain adhesive and frictional strength and net structure with established aggregates distribution and voids form, through the interactions among these components of asphalt mixture. The pavement performance consisting of high temperature stability, low temperature stability and water stability are directly influence on the void structure in the asphalt mixture. Therefore, it is pretty important to describe the distribution and volume of voids space in the stage of aggregate gradation design. According to the current domestic specification and engineering practice, there is only a parameter, void ratio, to express the void state in the asphalt mixture. It cannot evaluate the actual feature of voids in the asphalt mixture directly and effectively.According to the fractal theory, the fractal voids model and voids distribution density function of asphalt mixture were established in this paper. In the two-dimension analysis of voids in asphalt-mix, the void profile fractal dimension was counted by the digital image of section on Marshall specimen. On the basis of the fractal voids model, it can be obtained the value of voids area was increasing with the growth of the void profile fractal dimension. Meanwhile, the model of plane circle in bailey method simulated the voids structure of asphalt mixture. Combining the analysis method of fractal theory, the same conclusion of digital image analysis can be received. In the simulation of voids feature at three-dimensional space, the fractal dimension was directly related to the aggregate gradation of asphalt mixture. The volume of asphalt mixture voids can be calculated by the fractal voids model. Under the theory of the model, it can simulate the void gradation in the asphalt mixture. The results showed that the cumulative volume of the voids in 4.75×0.22 mm diameter was maximum in the total voids volume of asphalt mixture. Besides, the void ratio and aggregate voids ratio of asphalt mixture were measured by Marshall test. It formed contrast with the results of the fractal voids model.